TCFD Users Guide

User’s Guide Turbomachinery CFD Manual, version 17.06

CFD support s.r.o., Sokolovská Sokolovská 270/201, 19000 Praha 9, Czech Republic Republic [email protected] | phone: +420 212 243 883 | www.cfdsupport.com

Copyright

©2009-2017 CFD support s.r.o. All rights reserved. Any unauthorized reproduction of any form will constitute an infringement of the copyright. Trademarks

ANSYS is a registered trademark of Ansys Inc. BLENDER BLENDER is a registered trademark of The Blender Foundation. Foundation. CFX is a registered trademark of Ansys Inc. CHEMKIN CHEMKIN is a registered registered trademark of Reaction Reaction Design Corporation Corporation EnSight is a registered trademark of Computational Engineering International Ltd. Fieldview Fieldview is a registered trademark of Intelligent Intelligent Light Fluent is a registered trademark of Ansys Inc. GAMBIT is a registered trademark of Ansys Inc. Icem-CFD is a registered trademark of Ansys Inc. I-DEAS is a registered trademark of Structural Dynamics Research Corporation JAVA is a registered trademark of Sun Microsystems Inc. Linux is a registered trademark of Linus Torvalds ParaView is a registered trademark of Kitware STAR-CD is a registered trademark of Computational Dynamics Ltd. TCFD is a registered registered trademark of CFD Support s.r.o. s.r.o. UNIX is a registered trademark of The Open Group The OPENFOAM® related products and services are not approved or endorsed by OpenCFD Ltd. (ESI Group), producer of the OpenFOAM software and owner of the OPENFOAM® and OpenCFD® trade marks.

Contents 1

TCFD® Introduction 1.1 TCFD® = Turbomachinery CFD . . . . . . . . . . . . . . 1.2 TCFD® Unique Value . . . . . . . . . . . . . . . . . . . 1.3 Differences between TCFD® and standard OpenFOAM® . 1.4 Technical Specifications & Software Features . . . . . . . 1.5 What is included? . . . . . . . . . . . . . . . . . . . . . . 1.6 CFD Processor & TCFD® workflow overview . . . . . . . 1.7 Turbo Blade Post . . . . . . . . . . . . . . . . . . . . . . 1.8 ParaView . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8.1 ParaView License . . . . . . . . . . . . . . . . . .

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7 7 11 12 13 14 15 16 18 18

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TCFD® – Installation & First run 2.1 Windows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Linux . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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TCFD® – GUI Setup & Options 3.1 TCFDSource plugin . . . . . . . . . 3.2 General settings . . . . . . . . . . . 3.3 Coordinate system . . . . . . . . . 3.4 Geometry parameters . . . . . . . . 3.5 Physical settings . . . . . . . . . . . 3.6 Turbulence settings . . . . . . . . . 3.7 Speedline settings . . . . . . . . . . 3.8 Inlet boundary condition . . . . . . 3.9 Outlet boundary condition . . . . . 3.10 Simulation settings . . . . . . . . . 3.11 Numerical settings . . . . . . . . . 3.12 Initial conditions . . . . . . . . . . 3.13 Components . . . . . . . . . . . . . 3.14 Meshing options : Castellated mesh 3.15 Meshing options : Snap mesh . . . .

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Meshing options : Quality . . Meshing options : Layer mesh Post-processing . . . . . . . . Scripting . . . . . . . . . . . .

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TCFD® – Running & PostProcessing 4.1 TCFDManager plugin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 TCFDManager settings . . . . . . . . . . . . . . . . . . . . . . . . . . .

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5

TCFD® – Configuration File Options

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6

TCFD® – CFD Theory & Formulas 6.1 Formulas for the Efficiency Evaluation . . . . . . . . . 6.1.1 Hydro Turbine Efficiency . . . . . . . . . . . . 6.1.2 Pump Efficiency . . . . . . . . . . . . . . . . 6.1.3 Compressor Efficiency . . . . . . . . . . . . . 6.1.4 Turbine Efficiency . . . . . . . . . . . . . . . 6.1.5 Fan Efficiency . . . . . . . . . . . . . . . . . 6.2 Turbomachinery CFD Solvers . . . . . . . . . . . . . 6.2.1 blueSolver - steady state, incompressible . . . 6.2.2 blueDyMSolver - transient, incompressible . . 6.2.3 redSolver - steady state, compressible . . . . . 6.2.4 redDyMSolver - transient, compressible . . . . 6.2.5 greenSolver - steady state, cavitation . . . . . . 6.2.6 greenDyMSolver - transient, cavitation . . . . 6.2.7 Compressible Mathematical Model . . . . . . 6.2.8 Incompressible Mathematical Model . . . . . . 6.2.9 Unstructured Grid . . . . . . . . . . . . . . . 6.2.10 Finite Volume Method . . . . . . . . . . . . . 6.2.11 Three Dimensional . . . . . . . . . . . . . . . 6.2.12 Steady-State . . . . . . . . . . . . . . . . . . 6.2.13 Segregated Solver . . . . . . . . . . . . . . . 6.2.14 Cell Centered Approach . . . . . . . . . . . . 6.2.15 Under-Relaxation . . . . . . . . . . . . . . . . 6.2.16 System of Linear Equations . . . . . . . . . . 6.2.17 SIMPLE Algorithm . . . . . . . . . . . . . . . 6.2.18 Spatial Integration Numerical Scheme . . . . . 6.2.19 Temporal Integration Numerical Scheme . . . 6.2.20 Non-Orthogonal Correctors . . . . . . . . . . 6.2.21 Number of Iterations on Rotor and Stator Part . 6.2.22 Minimal and Maximal Values Options . . . . .

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TCFD® – Notes & Recommendations 7.1 General Notes & Recommendations . . . . . . . . . . . . . . . . . . . .

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Turbo Blade Post - graphical postprocessing 8.1 Geometry & Mesh . . . . . . . . . . . . . . . . . 8.2 Example: Meridional average . . . . . . . . . . . . 8.2.1 Step by step guide . . . . . . . . . . . . . 8.3 Example: Blade-to-blade view . . . . . . . . . . . 8.3.1 Step by step guide . . . . . . . . . . . . . 8.4 Example: Pressure around the blade . . . . . . . . 8.4.1 Step by step guide . . . . . . . . . . . . . 8.5 Example: Blade pressure and suction side contours 8.5.1 Step by step guide . . . . . . . . . . . . . 8.6 Meridional Average filter – details . . . . . . . . . 8.6.1 Input parameters . . . . . . . . . . . . . . 8.6.2 Averaging . . . . . . . . . . . . . . . . . . 8.7 Turbo Unwrap filter – details . . . . . . . . . . . . 8.7.1 Input parameters . . . . . . . . . . . . . . 8.7.2 Usage . . . . . . . . . . . . . . . . . . . .

6.3

6.4

6.5

6.2.23 Turbulent Flow . . . . . . . . . . . . . . . . . . 6.2.24 MRF . . . . . . . . . . . . . . . . . . . . . . . 6.2.25 Message Passing Interface (MPI) . . . . . . . . Notes on gravitational potential and hydrostatic pressure 6.3.1 Potential of a homogeneous gravitational field . . 6.3.2 Hydrostatic pressure . . . . . . . . . . . . . . . 6.3.3 Center of mass of a surface . . . . . . . . . . . . Water turbines - notes on calculations . . . . . . . . . . 6.4.1 Alternative formulation . . . . . . . . . . . . . . 6.4.2 Conclusion . . . . . . . . . . . . . . . . . . . . Interface between rotor and stator part . . . . . . . . . . 6.5.1 Frozen Rotor vs. Mixing Plane . . . . . . . . . .

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Chapter 1 TCFD® Introduction 1.1

TCFD® = Turbomachinery CFD

TCFD® is a comprehensive CFD workflow for turbomachinery simulations. This workflow covers complete process from the basic (usually CAD) data over CFD analysis to significant engineering results. TCFD® is based on the OpenFOAM® software. It is the final outcome of a many year development of the team of CFD Support engineers and developers.

TCFD® is not dependent on other software but it is fully compatible with standard OpenFOAM® and other software packages. It was originally designed for simulating rotational machines, nevertheless it can be used for a wide range of various CFD simulations.

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TCFD® 17.06 – User’s Guide • Pumps

• Nozzles & Diffusers

• Fans

• Steam Turbines

• Compressors

• Both axial and radial machines

• Turbines

• Both compressible and incompressible flows

• Hydro Turbines

• Ventilators

• Turbochargers

• Engine flows

The package includes the real tutorials. The tutorials help the user to operate the model data. The user can easily repeat the whole process with his own data.

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CFD Support s.r.o. provides full technical support. TCFD® is maintained and regularly updated. CFD Support engineers are instantly working on additional software modules and extensions covering even more physical problems. To ensure the smooth start the extensive training is provided. Experienced lecturer shows the full functionality and answers all the possible questions.

TCFD® is highly customizable. All the OpenFOAM® parts of the package are developed under GPL (GNU GENERAL PUBLIC LICENSE Version 3.) All the OpenFOAM® based components are provided with their source code. Having technical support, any additional functions can be added all over the workflow.

In TCFD® its developers made good use of many years experience with using and developing CFD software. Especially for this workflow were developed special OpenFOAM® based boundary conditions e.g. to handle the rotor - stator interface or boundary conditions for the inlet and the outlet of the computational domain. The solvers for TCFD® are very robust and they were heavily tested on real machine cases and showed perfect agreement with available measurements. The solvers are robust enough to handle ©2017 CFD support s.r.o.

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TCFD® 17.06 – User’s Guide

the extreme flow conditions, it shows excellent performance, for example, at transonic flows.

The TCFD® workflow also contains a number of scripts, OpenFOAM® utilities and OpenFOAM® function objects for preprocessing and postprocessing. To keep complete independence of this workflow, the computational mesh is created using OpenFOAM® utility snappyHexMesh. Of course using snappyHexMesh mesh is not necessary - any external CFD mesh can be imported and used instead.

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1.2

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TCFD® Unique Value

TCFD® is a smart, easy-to-use and affordable CFD software. TCFD® was designed for CFD simulations of all rotating machinery such as pumps, fans, compressors, turbines, turbochargers, hydro turbines, etc. Both radial and axial machines. Both compressible and incompressible fluid flows. It is based on OpenFOAM. Turbomachinery CFD is unique at least for four reasons:

1. TCFD® has No Licensing Policy - which means the users can keep Turbomachinery CFD forever and they can use it for unlimited number of users, jobs or cores. What is paid for is the first delivery and technical support and software maintenance. This gives the investment in Turbomachinery CFD a permanent value. And also this means our clients can scale their CFD simulations in a really big way.

2. TCFD® is fully automated - which means all the workflow from the initial data to the final results report, it can be run by a single command or a single click. And all the process is being done automatically. For this reason Turbomachinery CFD is extremely effective.

3. CFD Support delivers the extraordinary technical support. CFD Support keeps custom approach to every customer. To every issue. CFD Support never leaves behind any of its clients. Technical support is very flexible. Technical support is unlimited. CFD Support supports its clients even in matters out of the turbomachinery field. For example in: Numerical Mathematics, Physics, CFD, IT or even Software Engineering.

4. The real tutorials are included - so the TCFD® user has no doubts about the best practice settings. So there are included the real machines that are already preset. User can basically take one of those tutorials, replace the geometry with his own, you modify the settings and run the simulation. The rest of the workflow is automated anyway. So, the requirements on user’s CFD skills are very low.


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1.3

Differences between TCFD® and standard OpenFOAM® TCFD®

Standard OpenFOAM®

Commercial software

Open-source Code

YES

YES

NO

Unlimited Users, Jobs & Cores

YES

YES

NO

Robust Solver for Turbomachinery

YES

NO

YES

Turbo Boundary Conditions

YES

NO

YES

Real Tutorials for Turbomachinery

YES

NO

YES

Detailed Manual

YES

NO

YES

Turbo Pre/Postprocessing

YES

NO

YES

Automated Process (Workflow)

YES

NO

NO

Both Linux & Windows

YES

NO

YES

HTML Reporting

YES

NO

NO

Graphical Interface - GUI

YES

NO

YES

Free of Charge

NO

YES

NO

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13

Technical Specifications & Software Features

• Both Linux & Windows OS compatible

• Robust OpenFOAM® Solvers

• Fully Automated

• Meshing using SnappyHexMesh

• Compressible Flow

• Advanced Postprocessing

• Turbulent Flow • Heat Transfer between Fluid and Solid Parts • Both Subsonic and Transonic


• Fully Parallel Computing

• Convergence Monitoring • Special Boundary Function Objects

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Conditions

&

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1.5

What is included?

• OpenFOAM® based software + source code • Real Tutorials - preset test cases demonstrating how this workflow works on real examples • Applications - new robust solvers and utilities. • Libraries - special boundary conditions, function objects, flow models. • Scripts - preprocessing, postprocessing. • Software is Perpetual, Unlimited Users, Jobs & Cores • Source Code - all the source code of all GPL parts • Turbo Blade Post - Visual Postprocessing software • TCFDSource GUI - TCFD Graphical User Interface • CFD Processor - application for automated workflow • Training - tailored training covering individual needs of the client • Unlimited Technical Support • Updates & Maintenance until Technical Support is valid

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CFD Processor & TCFD® workflow overview

CFD Processor is designed for an effective handling of Turbomachinery CFD simulations. CFD Processor is an original product of company CFD Support s.r.o. (www.cfdsupport.com). It was especially created to enable an effective automation of a CFD process. The complete process is executed - reading the configuration file - creating new simulation case - CFD setup - simulation run - evaluation of CFD results - writing down the results report.

Figure 1.1: CFD Processor simple scheme

CFD Processor is a library – a set of routines – which is designed for • a straightforward setup of OpenFOAM cases, • automatic running of the calculations and • basic postprocessing of the calculated results. Internally, it uses the free OpenFOAM® toolbox – meshers, solvers and utilities – but saves the user from filling up large amount of necessary configuration files and managing the workflow of the computation. For this particular usage, a pair of plugins for the widely used ParaView (www.paraview.org) visualization software has been developed. The two ParaView plugins TCFDSource and TCFDManager serves as a Graphical User Interface (GUI) for TCFD® and both of them are described in this manual. • TCFDSource is used for an ease of use CFD case setup. • TCFDManager is used for an user friendly CFD simulation control. ©2017 CFD support s.r.o.

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CFD Processor solves for physical volume fields in a finite volume mesh created inside of a given boundary geometry. The machine is generally composed of several components (e.g. inlet piping, rotor, stator, outlet piping) that are meshed individually and have different construction properties. For the usage in CFD Processor each component should be provided separately as a set of non-overlapping ASCII STL (Stereo Lithography) geometry model files, which – put together – form the water-tight boundary geometry of the component’s volume or the external computational mesh could of each component can be imported. The summarized CFD Processor workflow is • [1.] Computational mesh generation - a brand new mesh can be generated on given STL files or the external computational mesh can be imported. • [2.] Simulation phase - it is possible to setup and simulate the whole machine characteristics (working points) in one simulation (e.g. different flow rates, different RPMs, different pressure ratios, etc.). • [3.] Results evaluation - the output is an html report with plots of interesting variables and colored pictures (e.g. blade-to-blade views, meridional averages, etc.). The third step can be done independently on the other two. It makes sense to run the post-processing stage even after the first point of the machine characteristics – to obtain detailed mesh information and interesting results of the first point (e.g. efficiency, pressure drop/rise, torque, etc.) in the synoptic html report.

1.7

Turbo Blade Post

Turbo Blade Post is a product of company CFD Support s.r.o. (www.cfdsupport.com). It was especially created to enable an effective graphical postprocessing of rotating machinery - both radial and axial machines such as pumps, hydro turbines, compressors, turbochargers, propellers and many more. Turbo Blade Post is a set of following plugins (filters) for ParaView (www.paraview.org): • Turbo Unwrap - for visualization of the blade-to-blade view or 2D plots around the blades. • Meridional Average - for evaluation and visualization of the meridional averages in the blade passage. More information about Turbo Blade Post can be found in the chapter 8 or on CFD Support web site: http://www.cfdsupport.com/turbo-blade-post.html. 16

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Figure 1.2: ParaView screen shot of Turbo Blade Post

Figure 1.3: Turbo Blade Post filters in ParaView menu


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1.8


ParaView

ParaView is an open source multiple-platform application for interactive, scientific visualization. It has a client–server architecture to facilitate remote visualization of datasets, and generates level of detail (LOD) models to maintain interactive frame rates for large datasets. It is an application built on top of the Visualization Tool Kit (VTK) libraries. Where VTK is a set of libraries that provide visualization services for data, task, and pipeline parallelism, ParaView is an application designed for data parallelism on sharedmemory or distributed-memory multicomputers and clusters. It can also be run as a single-computer application. ParaView offers the possibility to extend its functionality in several directions. This encompasses modifications to the GUI and implementation of new plugins.

1.8.1

ParaView License

ParaView uses a permissive BSD license that enables the broadest possible audience, including commercial organizations, to use the software, royalty free, for most purposes. In addition, there are other licenses that are applicable because of other packages leveraged by ParaView or developed by collaborators. Lastly, there are specific packages for the ParaView binaries available on paraview.org that have applicable licenses. Copyright (c) 2005-2008 Sandia Corporation, Kitware Inc.Sandia National Laboratories, New Mexico PO Box 5800 Albuquerque, NM 87185 Kitware Inc., 28 Corporate Drive, Clifton Park, NY 12065, USA Under the terms of Contract DE-AC04-94AL85000, there is a non-exclusive license for use of this work by or on behalf of the U.S. Government. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. Neither the name of Kitware nor the names of any contributors may be used to endorse or promote products derived from this software without specific prior written permission.

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Chapter 2 TCFD® – Installation & First run This introductory chapter summarizes the basic steps needed to obtain Turbomachinery CFD and run one of its preset tutorials. All combinations of operating systems (Linux/Windows) and user interfaces (console/graphical) are discussed. See also: http://www.cfdsupport.com/turbomachinery-cfd-workflow.html

2.1

Windows

1. Request the trial version (this is only for the trial version - in case you purchased the perpetual version - skip this step) http://www.cfdsupport.com/turbomachinery-cfd-demo.html

2. Download and install OpenFOAM® for Windows (including ParaView and Gnuplot): http://www.cfdsupport.com/download-openfoam-for-windows . html

3. Download and install TCFD® or TCFD® Demo (note: software versions have to match; e.g.: Turbomachinery CFD 17.06 fits to OpenFOAM® for Windows 17.06). 4. Download a tutorial: http://www.cfdsupport.com/download-cases.html

5. Copy two demo license files ( License.key and License.dat ) to the current OpenFOAM version directory, typically: C:\OpenFOAM\17.06\ * (this is only for trial version - in case you purchased the perpetual version - skip this step) 6. Ready to run now! 19

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7. Extract your tutorial into work directory, e.g.: C:\OpenFOAM\17.06\user-dev\run\pump

When using GUI:

8. Launch ParaView using the “TCFD 17.06” desktop shortcut or the corresponding item in the Start menu. 9. Open configuration file e.g. pump.tcfd in via the Load... button in the General section of the Properties panel located in the left area of the ParaView window.

10. Click Apply button. 11. In Pipeline browser select Settings and then apply TCFD Manager filter from the toolbar. 12. Click Apply, then Write Case and finally Run All.

13. And all the process is done automatically: new case is written into default case name ofcase0 , mesh is created, case is set up, case is simulated, results are evaluated and report is written down. 14. The report can be updated anytime during simulation.

15. When the simulation is finished the final results report is written down. It is located inside the test case: .\ofcase0\report-ofcase0\ofcase0.html

16. Visual postprocessing can be done in ParaView using Turbo Blade Post plugins (included). When using terminal:

8. Run OpenFOAM® for Windows command line. 9. Navigate e.g. to the pump directory (mc command – Midnight Commander – is recommended, or navigate manually in terminal) and run all by one command from the pump directory: CFDProcessor -setup pump.tcfd -allrun

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10. 10. And And all all the the proce process ss is done done autom automati atica cally lly:: new new case case is writt written en into into defa defaul ultt case case name name ofcase0, mesh is created, case is set up, case is simulated, results are evaluated and report is written down. When the simulation is finished the final results report is written down immediately immediately. It is located inside the test case: ./ofcase0/report-ofcase0/ofcase0.html

11. Visual postprocessing postprocessing can be done in ParaView using Turbo Blade Post plugins (included).

2.2

Linux

1. Request Request the trial version: version: http://www.cfdsupport.com/turbomachinery-cfd-demo.html

2. Download Download TurbomachineryCFD-17.06v1-linux64-demo.tar.gz 3. In terminal extract extract into your favorite favorite directory (e.g. (e.g. /home/michael/ ): tar xf TurbomachineryCFDTurbomachineryCFD-17.06v1-l 17.06v1-linux64-de inux64-demo.tar.gz mo.tar.gz

4. Download Download the tutorial: tutorial: http://www.cfdsupport.com/download-cases.html

5. Copy two two license license files files ( License.key License.key and License.dat ) to the directory TurbomachineryCFD-17.06v1-linux64-demo

6. Ready to run now! 7. In a new terminal source source the system variables variables (with every every new terminal, terminal, or add this to your $HOME/.bashrc for permanent permanent usage): source OpenFOAM/Turbomach OpenFOAM/TurbomachineryCFDineryCFD-17.06v1-l 17.06v1-linux64-de inux64-demo/etc/ mo/etc/ bashrc-release

8. Extract Extract your tutorial tutorial e.g. into your run directory: directory: /home/michael/OpenFOAM/michael-dev-cfdsupport/run/pump

When using GUI:

9. Launch ParaV ParaView iew by typing the command TCFD in the terminal. 10. Open Open configur configuratio ation n file e.g. pump.tcfd in via the Load... button in the General section of the Properties panel located in the left area of the ParaView window.

11. Click Click Apply Apply button. ©2017 CFD support s.r.o.

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12. In Pipeline Browser click Settings Settings and then apply TCFDManager filter from the toolbar. 13. Click Click Apply Apply, then Write Case and finally Run All.

14. And And all the proce process ss is done done autom automat atica icall lly: y: new new case case is writ writte ten n into into defaul defaultt case case name name ofcase0 , mesh is created, case is set up, case is simulated, results are evaluated and report is written down. down. 15. When the simulation is finished the final final results report is written down down immediately. immediately. It is located inside the test case: ./ofcase0/report-ofcase0/ofcase0.html

16. The report can be updated updated anytime during during simulation. simulation.

17. Visual postprocessin postprocessing g can be done in ParaView using Turbo Blade Post plugins (included). When using terminal:

9. In terminal terminal navigate navigate to the pump directory directory (mc – Midnight Commander – is recommended, or navigate manually in terminal) and run all by one command: CFDPro CFDProces cessor sor -setup -setup pump.t pump.tcfd cfd -allru -allrun n &

10. And And all the proce process ss is done done autom automat atica icall lly: y: new new case case is writ writte ten n into into defaul defaultt case case name name ofcase0 , mesh is created, case is set up, case is simulated, results are evaluated and report is written down. When the simulation is finished the final results report is written down immediately immediately.. It is located inside the test case: ./ofcase0/report-ofcase0/ofcase0.html

11. Visual postprocessin postprocessing g can be done in ParaView using Turbo Blade Post plugins (included).

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Chapter 3 TCFD® – GUI Setup & Options 3.1 3.1

TCFD TCFDSo Sour urce ce plug plugin in

The first part of the simulation is the setup. The plugin TCFDSource presents an intuitive graphical user interface (GUI) for the complete setup of a Turbomachinery CFD calcula calculation tion.. It is possible possible to save the data from the form to a file and also to read read them back, whenever necessary. When starting a new calculation, make sure that the TCFDSource plugin is loaded (Tools > Manage Plugins... ). If you can see the plugin in the list ("SMTCFDSource..."), you should be also able to locate the VTK source in the menu Sources (Sources > TCFD Source). Select that item; it will add a new object to the Pipeline Browser window. window.

Figure 3.1: Source TCFDSource added to the Pipeline Browser . A long form will appear in the Properties panel, which may become even longer, depending on the current settings, if you show the advanced options using the Toggle advanced properties properties button next to the search bar (wheel icon). Generally, the advanced properties have have universally universally reasonable values and are not necessary to modify. modify. Individual Individual sections of the form can be folded and unfolded by a single click on their header. Double click on a header will hide all other section than the one clicked. A new TCFDSource form contains contains default default values. values. It is also possible possible to import an already prepared Turbomachinery CFD setup file (with the *.tcfd extension) extension) into this form and start editing those. those. You can load a Turbomachinery CFD setup file by using 23

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the menu item File > Open... (or using the toolbar button, or the keyboard shortcut Ctrl + O) and selecting the file in the dialog window. Once the form is edited to your satisfaction, press Apply. This finalizes the setup and provides you with a concise table summarizing the options in the syntax of the Turbomachinery CFD setup files. Of course, it is possible to edit the entries even after clicking Apply. If you do, the Apply button will be enabled again and the changes need to be accepted anew. The TCFDSource plugin is relatively uncommon with regard to its output. While most built-in ParaView sources and filters have just one output, TCFDSource provides two outputs! These are clearly visible in the Pipeline Browser . The output "Settings" provides a table with raw settings, which can be saved as a *.tcfd file or passed to TCFDManager filter (described in the next chapter). The output "Components" provides the component geometry and is displayed in the common 3D RenderView. The state of the form can be saved as a Turbomachinery CFD setup file using the menu item File > Save Data... (or the appropriate toolbar button, or using the keyboard shortcut Ctrl + S). In the Save File: dialog first select the correct extension *.tcfd ; only then the correct plugin will be used for writing the data. The form must be confirmed by Apply before saving. The following sections provide details for individual form fields.

3.2

General settings

The general settings are displayed in the figure 3.2. • The entry "Setup file" contains full path of a Turbomachinery CFD setup file, which has been used to initialize the fields in the form. It is empty if no such file has been used. However, it is always possible to load a new file into the form by pressing "Load..." and selecting a new file from the dialog window. The other three buttons "Reload", "Save As..." and "Overwrite" have obvious meaning. The same restriction for the usage of File > Save data... holds also here: One must press Apply before saving the results. • The entry "Machine type" offers selection of the type of the machine that is to be set up. CFD Processor supports the following machines: fan, compressor, pump, turbine and hydro (water) turbine. Each of these types is slightly different, whether due to a different assignment of boundary conditions, or the postprocessing tools used.

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Figure 3.2: Plugin TCFDSource – general settings.

3.3

Coordinate system

The coordinate system section is displayed in the figure 3.3. • The entries "Origin" are the coordinates of the rotation axis origin. • The entries "Axis" are the components of the rotation axis direction vector.

Figure 3.3: Plugin TCFDSource – coordinate system.

3.4

Geometry parameters

The geometry parameters are displayed in the figure 3.4. • The entry "Scale factor" sets the scale of the length units to be used when processing the input geometry and some other form entries (namely "Origin", "Background mesh size", "Internal point", "Wheel diameter", blade clearance and distances to interfaces). If "1" is given, then CFD Processor assumes that all lengths and point coordinates are in meters, whereas if (e.g.) "0.001" is given, it is assumed that they are in millimeters. This setting is global: It is not possible to set different length scales for the geometry and for the form entries, or to have individual geometry files in different scales. Watch out!

It is extremely important to set the parameter "Scale factor" correctly as it defines the scale of the STL model. Wrong Scale factor will easily make the whole geometry ten- (hundred-, thousand-) times bigger or smaller than it is in reality, resulting in a completely meaningless calculation! ©2017 CFD support s.r.o.

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• The entry "Feature edges included angle" is a tuning parameter that specifies maximal angle (in degrees) that is considered "sharp" by the mesher. When two faces of a boundary geometry make an angle smaller or equal to this number, then their common edge will be preserved in mesh (the cells’ edges will be aligned with this line), otherwise it may be smoothed away. If zero is given, only open edges of the boundary geometry will be preserved.

Figure 3.4: Plugin TCFDSource – geometry parameters.

3.5

Physical settings

The physical settings are displayed in the figure 3.5. • The entry "Gravitational acceleration" sets the components of the gravitational acceleration vector. For most applications the gravitational force is negligible and these components can be zero. For large hydro (water) turbines it may be important. The typical setup with z axis pointing upwards would be the vector (0, 0, 9.81).

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• The drop-down list "Fluid name" offers selection of the fuild. This option has effect only with conjunction with "Use fluid defaults" or "Cavitation risk". • The switch "Use fluid defaults", when checked, hides some further fields and assumes default values for them that are appropriate for the selected fluid at standard conditions. These are summarized in the table 3.1. • The switch "Compressible" determines whether or not the fluid is considered compressible. When selected, then CFD Processor will also solve for the density and temperature fields, which are otherwise considered constant throughout the computational domain. The form automatically shows and hides entries that are relevant for the current choice. • The value of "Dynamic viscosity" specifies the dynamic viscosity (η ) of the fluid. For incompressible cases it is η = ρν , where ν is the kinematic viscosity. • The value of "Reference density" is used for postprocessing of incompressible cases, where the density is not considered by the solver. 26

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• The value of "Reference pressure" is used as a pressure value with respect to which all other pressures are measured. Typically, in incompressible simulation the user prescribes zero outlet pressure, while he or she actually means the ambient pressure. This entry then sets the ambient pressure. • The value of "Reference temperature" is the value of the ambient temperature and is used for postprocessing of "Cavitation risk". • The list "Transport model" can be used to select the preferred transport (viscosity) model. There two models available: "constant" and "Sutherland". When "Sutherland" transport model is selected, the entries "Ts" and "As" (parameters of the model) will show up. • The entry "Molar weight" is used only in compressible simulations to set up the thermophysical properties of the fluid. Molar weight is a standard chemical property of a substance. • The entry "Heat capacity" is used only in compressible simulations to set up the thermophysical properties of the fluid. The constant-volume heat capacity cV is expected. • The switch "Cavitation risk" can be used to request estimation of the cavitation. This switch is only available for "water" machines. The model was implemented according to following literature: [6], [17], [18]. • The switch "Multiphase cavitation" will request use of a specialized cavitation solver for the transient phase of the calculation. When this switch is enabled, additional cavitation-related parameters can be set. Currently there is only one cavitation model available for this solver – the Schnerr-Sauer model [5]. Multiphase cavitation is only available for water pumps and hydro turbines with transient calculation enabled.

3.6

Turbulence settings

Currently there are two turbulence models supported by TCFDSource: the laminar model , the k ω SST model (default) and the k  model. One of them can be selected in the section Turbulence settings and if the advanced parameters are enabled, the user can also tune parameters of the chosen turbulence model. The default values of the model parameters are shown in the figure 3.6.

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Figure 3.5: Plugin TCFDSource – physical settings: Incompressible (top) and compressible (middle) variants and fully enabled multiphase cavitation section (bottom).

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quantity

symbol

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unit

value air

dynamic viscosity reference density molar weight heat capacity Sutherland AS Sutherland T S Prandtl number heat capacity ratio

µ ρ M c p AS T S Pr γ

Pa s kg m 3 kg mol 1 J kg 1 K

· − K − −

· · ·

1.8

−

−

−

·

−1

water

× 10

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1.28 28.9 1004

−3

10

998 18.015 4181.8 −6

1.512 10

1.512 10

120 0.7 1.4

120 7 1.33

·

·

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Table 3.1: Fluid defaults used when "Use fluid defaults" is checked.

Figure 3.6: Plugin TCFDSource – turbulence settings: k


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3.7

Speedline settings

Every simulation consists of individual points with similar setup, which are grouped into speedlines sharing the rotation speed. Number of speedlines and number of points in every speedline is chosen in this section. Some other sections then adjust number of their inputs according to the numbers chosen here. • The slider "Speedlines" sets the number of speedlines (groups of points with common rotation speed). • The entries in "Rotation speed" set the rotation speed of the machine’s wheel for every speedline, either in radians per second or in full revolutions per minute (RPM). The unit is chosen in the drop-down box to the right. • The sliders in "Speedline points" set the number of points in every speedline. • The entries in "Point iterations" set the number of iterations of steady-state calculation used for each of the points. This actually sets the maximal number of iterations. If "Convergence check" is enabled, the solver may terminate even before the iteration count reaches this number, if it decides that the efficiency and the flows are sufficiently converged.

Figure 3.7: Plugin TCFDSource – speedline settings.

3.8

Inlet boundary condition

The inlet boundary conditions are displayed in the figure 3.8. There are several possible ways how to prescribe the desired behavior of the simulated fields at the inlet to the 30

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computational domain: Prescribing a fixed inflow (either in kg/s or m3 /s), or requesting a fixed total pressure. The choice of the boundary conditions is done by selection of one item of the drop-down list "Inlet BC". The rest of the panel is then adjusted to the user’s choice. There are two parameters that are common to all inlet boundary conditions. These two values set the parameters of the incoming flow turbulence. They are: • "Turbulent energy intensity" , which sets the fraction of the inlet turbulent and total kinetic energy k/ 12 ρU 2 , typically five per cent (0.05), and • "Turbulent dissipation", which sets the inlet turbulent dissipation rate ω within the k ω turbulent model, which is used by CFD Processor.

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The exclusive parameters of the "Mass flow rate" inlet boundary condition are: • "Mass flow rate", which is the inflow in kg/s. The exclusive parameters of the "Volumetric flow rate" inlet boundary condition are: • "Volumetric flow rate", which is the inflow in m3 /s. The exclusive parameters of the "Total pressure" inlet boundary condition are: • "Total pressure", which is the inlet total pressure ptot in Pa, • "Total temperature", which is the inlet total temperature T tot in K (only needed and available for compressible simulations) and • "Heat capacity ratio" γ (or sometimes κ ) is the ratio of the constant-pressure and constant-volume heat capacities, γ = c P /cV . The flow rate boundary conditions have also directed variants ("Directed mass flow rate" and "Directed volumetric flow rate"), which allow specification of the angle of the velocity vectors at inlet. This is done by setting the meridional and circumferential angle of the inlet direction. The inlet direction is a vector that points typically outside from the geometry and the velocity vectors will be oriented to be antiparallel with the inlet direction vectors (i.e. to point inwards). The meridional angle is the angle between the inlet direction vectors and the direction of the rotation axis. Allowed values of the meridional angle are between 0 and 180 degrees. The circumferential angle of the inlet direction vector at a given face is the angle between the inlet direction vector and the plane formed by the axis and the position vector of the given face. The range of the circumferential angles is from -90 degrees to +90 degrees, where positive angles correspond to positive orientation with respect to the rotation axis (right hand rule). ©2017 CFD support s.r.o.

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Figure 3.8: Plugin TCFDSource – inlet boundary conditions: Mass flow rate (top), directed mass flow rate (middle) and total pressure (bottom). The entry "Total Temperature" for total pressure boundary condition is only available in compressible simulations.

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Outlet boundary condition

The outlet boundary conditions are displayed in the figure 3.9. There are two possible ways how to prescribe the desired behaviour of the simulated fields at the outlet from the computational domain: Prescribing a fixed pressure or adjusting the pressure based on the outlet velocity. The choice of the boundary conditions is done by selection of one item of the drop-down list "Outlet BC". The rest of the panel is then adjusted to the user’s choice. The boundary condition "Fixed pressure" has only one editable property, of the same name. Its value is the wanted outlet pressure in Pa. The boundary condition "Outlet vent" adjusts the pressure based on the velocity: pBC = p + 21 RU 2, where R is the so called resistance. The parameters are • "Resistance", which specifies the outlet vent resistance R ; it can contain multiple resistance if multiple points are to be computed; • "Relaxation", which specifies the relaxation of the pressure fields between the iterations of the solver; • "Max pressure", which sets a pressure limit.

Figure 3.9: Plugin TCFDSource – outlet boundary conditions: Fixed pressure (top), and outlet vent (bottom).

3.10

Simulation settings

The simulation settings are displayed in the figure 3.10. ©2017 CFD support s.r.o.

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• The calculation mode can be chosen from the drop-down list "Time management". Here one can choose between a simple steady-state calculation, or its combination with some of the transient extensions, which will start from the precomputed steady-state results. The options are "transient" (classical transient calculation where all Mixing planes are replaced by face-weighted interpolation through AMI), "semi-transient (AMI)" (the same but with mesh motion replaced by MRF) and "semi-transient (MXP)" (as before, but the mesh from steady state case is kept intact, possibly thus containing Mixing planes). • The selection box "Transient source" allows one to select unit of time for specification of the length of the transient simulation. • The entries in "Transient revolutions" or "Transient times" are used to set the length of the transient simulation independently for every point. • The entry "Processors" specifies number of processes used to run the mesher and the solver. OpenFOAM uses MPI (Message Passing Interface) for communication of the processes. CFD Processor takes care for allocation and locking of the processes to the most free CPU cores. To achieve this it assumes that the OpenMPI 2.1.0+ is used on Linux-based systems and Microsoft MPI 7+ is used on Windowsbased operating systems. • If the advanced options are enabled, then the table "Hosts" is visible. It can be used in conjunction with the "Processors" entry to schedule the running of the parallel jobs. This table contains nodes, on which the parallel processes will be launched. The total number of processes given by "Processors" is evenly divided between the nodes. A new node is added by the plus button. This is by default the "localhost" node, but the word "localhost" in the first column can be edited (double-click to enable editing) to any other host name or IP address. The simple local network information provided by the system utility "getent" is then shown in the second column. If the node is unknown, the table row will turn red. Such nodes must be deleted, or the execution will fail. There are several restrictions on the usage of remote nodes: – All nodes must be accessible from the workstation where ParaView runs without password for the current user (i.e. using the public key authentication), and the same must be true for access between the nodes. – The MPI and OpenFOAM installations on the workstation and all the nodes must be identical. Ideally, there is just one installation on a shared network file system. – The OpenFOAM case directory is written on a shared network file system, so that it is accessible both to the front-end workstation used for solution management via ParaView and to the remote calculation nodes.

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Hosts scheduling is currently possible only in Linux systems. • The entry "Minimal pressure" sets the lower bound for the pressure. If there is a cell with a lower pressure after a solver iteration it will be adjusted to this value. This bounding can help in the beginning of the solution process, when the fields wildly oscillate iteration-to-iteration before stabilization. The minimal and maximal pressure bounds are given in numerical units, which is Pa in compressible calculation and Pa/(kg/m3) = m2 /s2 in incompressible calculation, and in both cases without contribution of the reference pressure. • The entry "Maximal pressure" sets the upper bound for the pressure. • The entry "Maximal velocity" sets the upper bound for the magnitude of the velocity. Larger vectors are scaled to this magnitude. • The entry "Minimal temperature" sets the lower bound for the temperature. This is only available for the compressible setup. • The entry "Maximal temperature" sets the upper bound for the temperature. This is only available for the compressible setup. • The entry "Minimal density" sets the lower bound for the density. This is only available for the compressible setup. • The entry "Maximal density" sets the upper bound for the density. This is only available for the compressible setup. • The entry "Numerical order" sets the discretization order of the convection term. All calculation should converge with the first order. The second order generally provides more accurate results, but the simulations are often less stable and may require better meshes or other tuning. • The switch "Convergence check" enables and disables automatic convergence check. If disabled, then CFD processor will always run the solver for specified amount of iterations. If enabled, then the solution of a particular point can terminate earlier. • The switch "Bind to core" prevent migration of solver processes between cores, possibly resulting in some speedup. (Currently only used in Linux-based systems.)


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Figure 3.10: Plugin TCFDSource – simulation settings: Incompressible (top) and compressible (bottom) variants.

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3.11

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Numerical settings

The under-relaxation factors and (in advanced mode) the number of non-orthogonal correctors can be changed in this section, see figure 3.11. Depending on the selection of incompressible or compressible calculation, the section offers modification of some or all of the following factors: pressure, velocity, density, temperature and turbulence. If available, the temperature and turbulence relaxation factors are always considered equal. The defaults are concisely summarized in the table 3.2. incompressible pressure velocity density temperature turbulence

compressible subsonic compressible transonic

0.2 0.5 — — 0.2

0.3 0.7 0.01 0.5 0.5

0.8 0.2 1.0 0.2 0.2

Table 3.2: Plugin TCFDSource – default relaxation factors for all possible setups. The compressible subsonic setup is used for fans, the compressible transonic setup is used for compressors and compressible turbines.

Figure 3.11: Plugin TCFDSource – relaxation factors.

3.12

Initial conditions

The initial conditions are displayed in the figure 3.12. • The entry "Initial pressure" sets a constant value of initial pressure throughout the computational domain. The solver will then iteratively improve this initial estimate. The pressure is given in Pa. • The entry "Initial velocity" sets a constant value of initial velocity throughout the computational domain. It is recommended that the initial flow follows the overall expected flow direction, typically along the rotation axis. ©2017 CFD support s.r.o.

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• The entry "Initial temperature" sets a constant value of initial temperature throughout the computational domain. • The entry "Initial k" sets a constant value of initial turbulent energy k throughout the computational domain. • The entry "Initial omega" sets a constant value of initial turbulent dissipation rate ω throughout the computational domain.

Figure 3.12: Plugin TCFDSource – initial conditions: Incompressible (top) and compressible (bottom) variants.

3.13

Components

A sample auto-generated component graph is displayed in the figure 3.13 and setup in the figure 3.14. The number of components is controlled by the slider (or edit field) "Number of components". When the number of components changes, the number of panels in this section and also in the advanced mesh properties panels is adjusted accordingly. Every component needs a water-tight boundary geometry divided into non-overlapping segments or a ready-to-use mesh. Currently there are three options for input of component mesh: • Directory with STL files – The directory must contain ASCII STL files which, when merged, give rise to a water-tight boundary surface. Every STL corresponds to an OpenFOAM patch (with a name taken from the name of the STL file), except for inlet, outlet and interface patches which are always merged. 38

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• Multi-solid STL file – The input is a single ASCII STL file containing multiple solids. Every solid must have a unique name within the STL file. That name will be used for naming the patch. • External OpenFOAM mesh – The patches (and mesh) are taken from an already existing OpenFOAM mesh. The mesh creation step for this component will be skipped. Every patch has several properties. First of all, it is the patch type, which is one of the following: • empty – Boundary in non-physical, artificial, dimension; used in two-dimensional simulations. • symmetry – Special symmetry boundary condition for calculation of just a half of a perfectly symmetrical system. • inlet – Entry to the simulated machine, mostly to the first component. • inletInterface – Entry to other components, connected to some preceding component. It is necessary to connect this interface to a specific component by rightclicking on the row and selecting the component. This change will be reflected in the component graph. • outlet – Exit from the simulated machine, mostly the last component. • outletInterface – Exit from other components, connected to some following component. It is necessary to connect this interface to a specific component by rightclicking on the row and selecting the component. This change will be reflected in the component graph. • cyclicAMI – Periodic interface in simulation of a segment. It is necessary to connect this interface to another "cyclicAMI" interface within the same component by rightclicking on the row and selecting the patch. This change will be indicated by a colour change of the rows. • internalAMI – Internal non-conformal mesh iterface. It is necessary to connect this interface to another "internalAMI" interface within the same component by rightclicking on the row and selecting the patch. This change will be indicated by a colour change of the rows. • rotationAMI – Patches on the boundaries of a segment, which are (periodically) mapped to each other. It is necessary to connect this interface to another "rotationAMI" interface within the same component by right-clicking on the row and selecting the patch. This change will be indicated by a colour change of the rows. ©2017 CFD support s.r.o.

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• wall – General no-slip wall. • wallSlip – General perfect-slip wall. • hub – A specific type of wall. • shroud – A specific type of wall. • blade – A specific type of wall. • bladePressureSide – A specific type of wall. • bladeSuctionSide – A specific type of wall. • bladeLeadingEdge – A specific type of wall. • bladeTrailingEdge – A specific type of wall. • bladeHubFillets – A specific type of wall. • bladeShroudFillets – A specific type of wall. • bladeCap – A specific type of wall. • cutWater – A specific type of wall. Besides the specific type, every patch can be either rotating or non-rotating, which is controlled by a check-box in the column labeled "rot". Further columns contain the minimal and maximal refinement and number of layers, which are used during the meshing. It is possible to change the value by double-clicking on the required field and either modifying the value by hand or using the spin-box buttons. Finally, the column "mxp", available only for inlet and outlet interface patches, contains the number of Mixing planes . If "0" is given, the components will be connected using cyclicAMI; higher values specify number of Mixing plane strips to use. Some columns may not be present for specific geometry sources (e.g. for an external OpenFOAM mesh). Further options in this section are • "Component name", which sets the name of the component used in patch names and report. • "Surface hook-up", which corrects some non-water-proof STL boundaries, • "Rotating component", which makes the whole component rotate (needed for all componets containing the wheel), • "No. periodic segments", which is used to set periodicity of a segment when simulating just a segment of the full wheel, 40

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• "Background mesh size" , which sets the basic cell size in the three directions for the rectangular background mesh (all cells will be such or smaller), • "Internal point", which specifies arbitrary internal point, • "Wheel diameter", which is a mandatory parameter only for the "fan" machine and is used for post-processing, • "Cylindrical mesh", which uses cylindrical background mesh instead of the rectangular, see figure 7.1, and enable the following three parameters, • "Cylindrical radii", which sets the parameters r1 , r2 and r3 of the cylindrical mesh, • "Cylindrical grading", which sets the parameters g1 , and g2 of the cylindrical mesh and • "Cylindrical warp", which sets the parameter w of the cylindrical mesh. If a cylindrical background mesh is selected, then the interpretation of "Background mesh size" changes. Instead of cell sizes in the x , y and z axes it sets the approximate cell sizes in radial, circumferential and axial directions (with respect to the chosen axis). The component graph (shown in the figure 3.13) displays all components and their interfaces. Thick arrows point always from inlet to outlet interface. If some interface is not available (or connected), the arrows become dashed and point elsewhere. This then indicates an invalid topology. Generally all components must be reachable from the inlet component and must be connected using the inletIterface/outletInterface pairs. The figure can be released from the panel by double-click; this transfers it to a new window. The separated window stays by default on top of all other windows (this can be manually unselected in the window manager menu). Further double-click merges the window back into the panel, as does also closing the window in any other way. The colours in the graph correspond to colours of the individual components in RenderView, assuming the colouring by vtkBlockColors is chosen.

3.14

Meshing options : Castellated mesh

The default panel is displayed in the figure 3.16. The most important numbers are the refinement levels (minimal and maximal) for individual patches. The mesher will subdivide the cells of the background mesh a few times. The count of these subdivisions is always in the given interval and depends on the vicinity of other patches and the local curvature. The remaining parameters are: • The switch "Castellated mesh" enables and disables the castellated mesh phase. For normal operation it is always enabled. ©2017 CFD support s.r.o.

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Figure 3.13: Plugin TCFDSource – component graph.

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Figure 3.14: Plugin TCFDSource – component setup.

Figure 3.15: Plugin TCFDSource – component setup – connecting the cyclicAMI patches.


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• The value "Max global cells" sets a hard limit on the total number of cells to prevent memory overflow. • The value "Max local cells" sets a soft limit on the number of cells per meshing process. When reached, the redistribution of the cells between the processes is done in a more careful (and slower) way. • The value "Min refinement" sets a limit on the lowest number of cells refined in previous iteration of the mesher, which still triggers another iteration. If zero is given, the mesh will be refined ideally according to the algorithm of the mesher. Slightly higher values speed up the castellated mesh phase of the meshing without great impact on the quality of the mesh. • The value "Max load unbalance" is the largest relative difference in number of cells across the mesher’s processes, which is considered low and does not trigger (slow) redistribution. • The value "Cells between levels" sets the minimal number of consecutive cells of a single refinement level in area where the refinement level dramatically changes. • The number "Resolve feature angle" is an angle in degrees.

Figure 3.16: Plugin TCFDSource – advanced mesh setup: Castellated mesh.

3.15

Meshing options : Snap mesh

The default panel is displayed in the figure 3.17. The switch "Snap mesh" enables and disables the snap mesh phase. For normal operation it is always enabled. The other parameters can be used to tune the mesher operation. 44

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Figure 3.17: Plugin TCFDSource – advanced mesh setup: Snap mesh.

3.16

Meshing options : Quality

The default panel is displayed in the figure 3.18. The parameters can be used to tune the mesher operation.

Figure 3.18: Plugin TCFDSource – advanced mesh setup: Quality.

3.17

Meshing options : Layer mesh

The default panel is displayed in the figure 3.19. The switch "Add layers" enables and disables the layer mesh phase, where a boundary layer is added to the walls. The user can ©2017 CFD support s.r.o.

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select number of boundary layers per a patch group (hub, shroud, blade cap, etc.). The other parameters can be used to tune the mesher operation.

Figure 3.19: Plugin TCFDSource – advanced mesh setup: Layer mesh.

3.18

Post-processing

This section allows user to define how the post-processing (evaluation of results and generation of a report) will be done. • The entry "Averaging window" sets the number of iterations used for calculation of the averaged fields. Also, this interval is used to monitor convergence: If the efficiency, inflow and outflow change negligibly during the window, the point is deemed converged. Also, it acts as a smoothing interval for the figures in the resulting report. • The entry "Transient window" is an analogue of "Averaging window" in a transient calculation. It can be given either in seconds, or in revolutions. • The entry "Snapshot interval" has only effect in a transient calculation. It serves for regular write-out of the results during the calculation, so that they can be later used e.g. to construct an animation. 46

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• The table "Efficiency probes" has by default a single generic row, which corresponds to the default report being generated. Every row of the table defines inlet, torque and outlet patches. It is possible to add more rows to this table with different contents, so that more reports will be generated for the chosen evaluation method. The inlet and outlet patches are used to calculate mass flow and total pressure difference, the torque patches are used to calculate the torque expended by the fluid/blade (depending on the machine). Together, they are used to evaluate efficiency and other quantitites. The switch "convergence" determines whether this particular probe is considered by the convergence check; the calculation will be stopped as converged only when all probes with enabled "convergence" switch sufficiently converge. • The table "Blade to blade views" contains a list of requested blade-to-blade views (circularly unwrapped and slices meshes) to be generated by Turbo Blade Post. The column "meshes" contains a list of meshes that will be unwrapped. It is possible to use both the internal meshes and individual patches. The hub and shroud patches must be provided in the next two columns as they define the requested transformation of the mesh. The column "fields" is used to select the field that will be displayed on the blade-to-blade view. Finally, "heights" contains a space-separated list of positions between the hub and the shroud where the blade-to-blade views will be taken. • The table "Meridional averages" contains a list of meridional averages to be generated by Turbo Blade Post. It can be used only with component indices, but otherwise the meaning of its columns is identical to "Blade to blade views". • The table "Additional data files" is used to add user data to the graphs in the final report from the calculation. The data should be provided in the form of Gnuplotreadable data files, i.e. text files with white-space-separated equal-length columns of numbers. The graph into which the data are to be added is chosen in the second column, the column indices to be used in the remaining two (first column has index 1). Several data-lines within a single data file can be achieved by interrupting the columns by an empty row; this is useful particularly in the multi-speedline summary diagrams (their name ends with "-all").

3.19

Scripting

For experienced users it is possible to extend the Turbomachinery CFD workflow by custom scripts. These scripts are expected to be written in basic Python 2 and they are executed in specific moments during the workflow. It is allowed to assign multiple execution points to a single script, see figure 3.21. The script can use the predefined variable CaseDirectory, which contain the full absolute path to the directory ©2017 CFD support s.r.o.

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Figure 3.20: Plugin TCFDSource – post-processing. with the OpenFOAM case. Besides the standard Python functions one can also use the TurbomachineryCFD-specific functions SetEntry and WriteFile . For example the following tiny script SetEntry("system/fvSolution", "solvers/p/nCellsInCoarsestLevel", "10") WriteFile("system/fvSolution")

will change the coarsest-level cell number in pressure GAMG solver to 10, followed by writing the modified file. The function SetEntry does all modifications in memory and the result is written to disk only when the function WriteFile is used, or during writing requested by the workflow. Apart from the two functions, there is also a predefined string variable CaseDirectory which contains the absolute path to the case and two other access functions RenameEntry(, , ) DeleteEntry(, )

with obvous purpose: The former changes the name of an entry (i.e. the keyword that introduces the entry), whereas the latter erases the whole entry from the file.

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Figure 3.21: Plugin TCFDSource – addition of custom user scripts to be executed during the workflow.


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Chapter 4 TCFD® – Running & PostProcessing 4.1

TCFDManager plugin

The second part of the simulation is the calculation and its postprocessing. The plugin TCFDManager offers a simple user interface for these two tasks in the framework of Turbomachinery CFD. It builds on the plugin TCFDSource described in the previous chapter. When starting a new calculation, make sure that the TCFDManager plugin is loaded (Tools > Manage Plugins... ). If you can see the plugin in the list (“SMTCFDManager...”), you should be also able to locate the VTK source in the menu Filters (Sources > Alphabetical > TCFD Manager or Sources > Turbomachinery > TCFD Manager ). Select that item; it will add a new object to the Pipeline Browser window. Note that the filter TCFDManager can be used only together with TCFDSource. An instance of TCFDSource (or its “Settings” output port) must be selected in the Pipeline Browser for TCFDManager to be even selectable!

Figure 4.1: Filter TCFDManager added to the Pipeline Browser .

The user interface of the TCFDManager is much simpler than that of the TCFDSource. The following sections provide details for individual form fields. 51

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4.2

TCFDManager settings

The filter are displayed in the figure 4.2. • The field “Output path” is a working directory, where new calculations are to be created. If the TCFDSource has been initialized by a Turbomachinery CFD setup file, this field will be already filled with the directory containing the file, or – if such directory is an OpenFOAM case directory – by its parent directory. • The field “Directory name” is the name of a new directory containing the next calculation to be done. There are several possible scenarios for this option: – If the TCFDSource has been initialized by a Turbomachinery CFD setup file and that file is already inside of an OpenFOAM case directory, then that directory name will be used here making the CFD Processor use the already calculated data and, if needed, overwrite them with new results. – If the loaded setup file is not located inside of an OpenFOAM case, then the directory name will be left empty. – In any case, the use may decide to specify an own name and press Apply.

• The button “Write case” will write a new OpenFOAM case into the directory specified by the combination of the above two fields. If no “Directory name” is given, CFD Processor will provide some directory name, which is not yet used in the “Output path”, and put the OpenFOAM case in there. This automatically suggested directory name is always in the form “ofcaseX”, where X is lowest non-negative integer available. Note that when “Directory name” is set, then whenever the Apply button is pressed, this “Write case” action will be done automatically. • The button “Write + Clean case” will first write the case files corresponding to the current setup and then erase all other files from the case. This is useful when restarting a calculation with different settings. Use it carefully, you may lost old data. • The button “Run all” will take care of rest of the steps. It will mesh the domain, solve the fields and evaluate results. If more control is required, the user can use the buttons in the “Manual Run” sections. • The buttons “Build” can be used to prepare the mesh of a component. This needs to be done even for external meshes (those can be distinguished by the note “(ext)” displayed in the title of the component), so that the patches are renamed and mesh is analyzed and copied to the appropriate destinations. The progress of meshing is indicated by elapsed time displayed on the button. The button “Merge” is used to concatenate meshes of individual components and create the final merged mesh of 52

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the whole machine. The effect of the button “Mesh all” is equivalent to using all “Build” buttons and the “Merge” button. The “Merge” button cannot be used until all components are successfully meshed. The success is indicated by a change of colour. Red colour means no mesh, yellow colour means invalid mesh (or meshing in progress), green colour means valid mesh. • Once a component’s mesh (or merged mesh) is ready, it can be displayed. To display the mesh toggle the “Show” button and click “Apply”. Depending on the actual layout of ParaView panels, the user may need to open a RenderView window and display the loaded mesh by clicking on the eye symbol next to the “Mesh” output of the TCFDSource filter in the Pipeline Browser . • The button “Run calculation” will run the second stage of the workflow: calculation of the physical fields for each simulation point. The progress of each point is shown in the point progress bar (“Point (stead)”) and the progress of the whole calculation, which can be composed of a sequence of points, is shown in the calculation progress bar (“Calculation (stead)”), see figure 4.4. There are also the unsteady progress bars if the setup includes a transient run. • The button “Skip to next point” can be used during the calculation e.g. when the currently calculated point seems to be converged and the user wants to continue with the next point. Note that there is always a delay between pressing the button and skipping action, which amounts to one or two iterations. • The button “Abort calculation” will gracefully terminate the calculation allowing for further use of ParaView. Note that there is some delay between pressing the button and the termination itself. • The button “Abort calculation (+ write)” is similar to the previous with the addition that the current state of the calculation is written out before termination. This is useful for debugging purposes. • The button “Update report” will regenerate the report containing various extracted data, like the residua, efficiencies, pressure information etc. Some of the values and plots may not be available until the end of the run. The report is a HTML document, which can be displayed in the HTML View panel, see 4.6. The report update is generally fast, but for long transient calculations or calculations with many points and speedlines it can take even a few minutes. The progress is indicated in the adjacent progress bar. The report is also automatically updated at the end of the calculation. Moreover, one can set the auto-refresh interval (in minutes) in the editable field above the progress bar (and confirm Apply). If a positive value is set, it will be used during the calculation. ©2017 CFD support s.r.o.

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• “Light report” has a simillar function as “Update report”, but produces only a subset of the full report, particularly the “Efficiency”, “Head” and “Total pressure difference” sections. This is useful to monitor convergence of these results during the calculation. • The button “Show results” will open the OpenFOAM calculation selected in the drop-down list “Results” using the built-in OpenFOAM reader. There is one case for the whole stationary simulation and separate cases for individual points of the transient calculation. When the Apply button is pressed, the TCFDManager will call CFDProcessor to analyze the settings. This involves also inspection of the provided geometry and may take a while. The progress of geometry analysis is shown on the ParaView’s main progress bar. If ParaView was launched from a Unix terminal, it is possible to read some diagnostic information in the terminal. This information comes directly from the CFD Processor libraries. Alternatively, the user can enable the Turbomachinery CFD output window from the menu View, which contains the same information.

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Figure 4.2: Properties of the TCFDManager filter.


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Figure 4.3: Meshing progress in TCFDManager showing the elapsed time.

Figure 4.4: Point and calculation progress indicator of TCFDManager. Apart from the graphical representation, it shows the index of the point currently being solved, number of iterations finished, number of iterations in total and estimated remaining time. In transient calculation (below) the iterations are replaced by the simulated time. The bottom three progress bars are only available for a transient calculation.

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e m u l o v d e r u t c u r t s n u g . n ) i t w l o u s d e n r i e w h t w e d i n V a r e ) d w n o e d R n t i h w i g r w ( e i r e V h r s e d e n m e R h t s e f e M l , x h e s H e m y p e p c a a n f r s u e s h ( t s g t n i n e s n u o r p m o o s c s t e u c p o r n P i e D h t F f C o y w b e d i e V t a : r 5 . e 4 n e g e r h u s g e i F m


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F i g u r e 4 . 6 : V i e w o f t h e fi n a l r e p o r t f r o m t h e

C F D P r o c e s s o .r

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Chapter 5 TCFD® – Configuration File Options The Turbomachinery CFD file produced by TCFDSource has mostly the *.tcfd extension. It is a human-readable plain text file where every line falls into one of the following categories: • Empty line. • Comment, introduced by a hash sign (‘#’). • Keyword–values pair. The keywords are strings uninterrupted by a whitespace character. They contain only alphanumerical characters, numbers, dashes and underscores. Every keyword can be generally set to an arbitrary number of values. A value is a string uninterrupted by a whitespace character. Some keywords have a special structure “N_something”, where “N” is a positive number. These are used to assign properties to individual components, speedlines, working points, post-processing modes etc. A complete list of recognized keywords, together with some sample values and explanation, is presented in the table at the end of this chapter. Both the UNIX-like (LF) and Windows (CR+LF) line endings are supported on both UNIX-like and Windows operating systems. Here is a sample of a TCFD file: 1 # Machine type 2 type 3 4 # Simulation settings 5 processors 6 numberOfSpeedlines 7 1_numberOfPoints 8 1_iterations 9 10 # Operating point 11 angularVelocity

AF-nq105 fan

6 1 16 500 500 500 500 500

-471.238898038469

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60


12 inletBoundaryCondition 13 volumetricFlowRate 14 outletBoundaryCondition 15 fixedPressure 16 in letT urbu lentE nerg yInt ensit y 17 inletTurbulentDissipation 18 UMax 19 pMin 20 pMax 21 22 # Physical settings & Fluid properties 23 fluidName 24 compressibility 25 referenceDensity 26 dynamicViscosity 27 gravitationalAcceleration 28 referencePressure 29 referenceTemperature 30 31 # Initial condition settings 32 initialPressure 33 initialVelocity 34 initialTurbulentEnergy 35 initialTurbulentDissipation 36 37 # Geometrical information 38 scaleFactor 39 origin 40 axis 41 numberOfRegions 42 43 # Information of region 0: Impeller 44 1_componentName 45 1_wheelDiameter 46 1_filePath 47 1_internalPoint 48 1_backgroundMeshSize 49 1_inlet 50 1_2_outletInterface 51 1_2_outletInterface-mixingPlanes 52 1_shroud 53 1_hub 54 1_blade 55 1_blade-refinementSurfaces 56 1_rotatingRegion 57 1_rotatingPatches 58 59 # Information of region 1: Vaned stator 60 2_componentName 61 2_wheelDiameter 62 2_filePath 63 2_internalPoint 64 2_backgroundMeshSize 65 2_1_inletInterface 66 2_1_inletInterface-mixingPlanes 67 2_outlet 68 2_outlet-refinementSurfaces 69 2_shroud 70 2_hub 71 2_blade 72 2_blade-refinementSurfaces 73 2_rotatingRegion

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volumetricFlowRate 5 4.75 4.5 4.25 4 fixedPressure 0 0 0 0 0 0 .05 100 1000 -50000 50000

Air incompressible 1.2 1.842E-5 0 0 0 101325 293.15

101325 0 0 9.74014381911833 0.001 100

0.001 0 0 0 0 0 1 2

impeller 340 ./STL 11.5 -161 28.4 30 30 30 impeller-inflow impeller-outflow 10 impeller-shroud impeller-hub impeller-blades 2 4 true impeller-shroud impeller-hub impeller-blades

stator 0 ./STL 155 -11.5 85.1 20 20 20 vanedGate-inflow 10 vanedGate-outflow 2 4 vanedGate-shroud vanedGate-hub vanedGate-blades 3 4 false

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© 2 0 1 7 C F D s u p p o r t s .r . o .

Keyword

type processors

Mandatory

fan

− −

yes

−

no

−

no

−

no

−

no

−

yes

−

yes

−

yes

s

no

−

no

4

 Number

no

of CPU cores used for simulation. Default = 1. If processors > 1, then a domain-decomposition solution with MPI communication is used.

bindToCore

 Lock

true

processes to cores to prevent their migration. This is currently active only in Linux.

node1 node2 node3  List of remote

machines for scheduling parallel processes. Paswordless login must be available. Currently active only in Linux.

transient

no | yes | semiAMI | semiMXP

 Append transient

simulation after stationary. Default is “no”. The semi-transient modes “semiAMI” and “semiMXP” use MRF method instead of physical rotation, albeit with time derivatives.

Co

0.9 

Courant number (transient simulations only).

numberOfSpeedlines  Number

 Number

1000 1000 1000 of iterations for each point of a speedline.

1_transientTime  Running

1.0 1.0 1.0

 Running

s u p p o r t @ c f d s u p p o r t . c o m

time of transient simulation in seconds.

1_transientRevolutions pMin

3

of points for the first speedline. All speedline points share rotational speed.

1_iterations  Number

3

of speedlines (different rotation speeds).

1_numberOfPoints

6 1

Units

 Machine class, one of: fan, pump, turbine, waterTurbine, compressor.

hosts w w w . c f d s u p p o r t . c o m

Allowed / sample values

 Description

555

time of transient simulation in impeller revolutions.

-2000

Pa (m2 /s2 ) no

6 1

6 2

Keyword


Units

Mandatory

6 2

 Description  Bounding

pMax

5000

 Bounding

UMax

value for pressure for robust convergence. Pascals assumed in compressible case, kinematic pressure in incompressible

case.

value for pressure for robust convergence. Pascals assumed in compressible case, kinematic pressure in incompressible

case.  Bounding

 Bounding

20

kg/m3

no

273.15

K

no

1000

K

no

0.2

−

no

0.5

−

no

1

−

no

0.2

−

no

−

no

Velocity under-relaxation factor.

rho_relax  Density

tt_relax 

no

Pressure under-relaxation factor.

U_relax 

kg/m3

value for robust convergence.

p_relax 

© 2 0 1 7 C F D s u p p o r t s .r . o .

0.1


TMax  Bounding

no


TMin  Bounding

m/s


rhoMax  Bounding

1000 value for robust convergence.

rhoMin w w w . c f d s u p p o r t . c o m

under-relaxation factor.

Temperature and turbulence under-relaxation factor.

X_tolerance  Linear

Pa (m2 /s2 ) no

1E-8 solver tolerance for quantity X = p, U, h, ...

T C F D ® 1 7 . 0 6 – U s e r ’ s G u i d e

© 2 0 1 7 C F D s u p p o r t s .r . o .

Keyword

X_relTol  Linear

Mandatory

1E-3

−

no

−

no

first

−

no

100

−

no

− (s)

no

0

s

no

true

−

no

−

no

scripts/run.py afterWrite

−

no

-185 -190 -195

rad/s

yes*

RPM

yes*

0

 Non-orthogonality-compensating

nested pressure iterations.

numericalOrder 

“First” or “second” numerical order.

 Averaging window for stationary calculation. Does the averages over last n iterations. Checks convergence for last n iterations.

transientWindow

0.1_revolutions

 Averaging window

for transient calculation. Use the suffix _revolutions or _seconds to determine units for the time interval.

snapshotInterval 

Secondary write for transient calculation.

convergenceCheck  Monitor

convergence and auto-skip to next point when convergence has been reached.

convergenceCheck-tolerance  Relative



0.001

convergence threshold for efficiency and mass flow.

userDefinedFunctions Custom user script setup.

angularVelocity  Rotation

 Rotation

-1770 -1870 -1970 speeds for all speedlines. *) Use either this keyword or “angularVelocity”.

inletBoundaryCondition  Inlet


speeds for all speedlines. *) Use either this keyword or “revolutions”.

revolutions

6 3

Units

solver relative tolerance of quantity X = p, U, h, ...

nonOrthoCorrectors

averagingWindow w w w . c f d s u p p o r t . c o m


 Description

massFlowRate

−

yes

boundary condition to use. Possible options are: massFlowRate, directedMassFlowRate, volumetricFlowRate, directedVolumetricFlowRate, totalPressure.

6 3

6 4

Keyword


Units

0.126 0.124 0.120

kg/s

Mandatory

6 4

 Description

1_massFlowRate

yes*

 Boundary

condition values for all points of the first speedline for BC of type “massFlowRate”. The index of speedline can be omitted if there is only one speedline.

1_volumetricFlowRate  As above, for

w w w . c f d s u p p o r t . c o m

 Additional

 Additional

1000 900 800

K

yes*

90 0 outletVent | fixedPressure 048 0.1

Outlet vent boundary condition relaxation factor value. Only for experienced users.

deg

yes*

deg

yes*

−

yes

−

yes*

−

yes*

200000

Pa

yes*

Pa

yes*

Outlet vent boundary condition maximum outlet pressure value.

1_fixedPressure  Average

100000 110000 120000 oulet pressure value for all points of the first speedline.

inletTurbulentEnergyIntensity 

yes*

Outlet vent boundary condition resistance factor values for individual points of the first speedline.

outletVentMaxPressure 

Outlet boundary condition to use. Possible options are “outletVent” and “fixedPressure”.

outletVentRelaxation 

Pa

parameter for “directedMassFlowRate” and “directedVolumetricFlowRate” boundary conditions.

outletBoundaryCondition



200000 150000 100000

parameter for “directedMassFlowRate” and “directedVolumetricFlowRate” boundary conditions.

1_circumferentialAngle

1_outletVentResistance © 2 0 1 7 C F D s u p p o r t s .r . o .

yes*

condition values for temperature in compressible calculations for the first speedline.

1_meridionalAngle



BC of type “totalPressure”.

1_totalTemperature  Boundary

m3 /s

BC of type “volumetricFlowRate”. Used for incompressible calculations.

1_totalPressure  As above, for

0.126 0.124 0.120

Turbulent intensity, typically 2%-5%.

0.05

−

yes

T C F D ® 1 7 . 0 6 – U s e r ’ s G u i d e

© 2 0 1 7 C F D s u p p o r t s .r . o .

Keyword

inletTurbulentDissipation  Boundary

Mandatory

100

1/s

yes

−

yes

 Name

−

yes

1.2

kg/m3

yes

0.000018

Pa s

yes

000

m/s2

no

Pa

yes

water | air of the fluid. Used for various material properties defaults.

compressibility 

incompressible | compressible

Fluid flow nature: compressible or incompressible.

 Reference density of the fluid.

dynamicViscosity  Dynamic



Gravity in Cartesian coordinates (x y z components).

referencePressure  Reference

 Reference

293.15

K

yes*


temperature. *) Only used in compressible calculations.

sutherland | constant

−

no

0.7

−

no

1.512e-06

−

no

120

K

no

Viscous transport model.

Pr 

101325

pressure. All other pressures will be considered relative to this one.

referenceTemperature



·

viscosity of the fluid.

gravitationalAcceleration

transport

Constant transport parameter (Prandl number, default air: 0.7, water: 7)

As 

Sutherland transport parameter.



Sutherland transport parameter.

Ts 6 5

Units

condition for turbulent dissipation rate (omega).

fluidName

referenceDensity w w w . c f d s u p p o r t . c o m


 Description

6 5

6 6

Keyword


Units

Mandatory

kOmegaSST | kEpsilon

−

no

0.85

−

no

1

−

no

0.5

−

no

0.856

−

no

0.075

−

no

0.0828

−

no

0.09

−

no

0.5555556

−

no

0.44

−

no

0.31

−

no

1

−

no

6 6

 Description

turbulence 

Turbulence model.

kOmegaSST-alphaK1 

Parameter of the k-omega SST model.

kOmegaSST-alphaK2 


kOmegaSST-alphaOmega1 w w w . c f d s u p p o r t . c o m






kOmegaSST-beta1 


kOmegaSST-beta2 


kOmegaSST-betaStar 

© 2 0 1 7 C F D s u p p o r t s .r . o .


kOmegaSST-alphaOmega2


kOmegaSST-gamma1 


kOmegaSST-gamma2 


kOmegaSST-a1 


kOmegaSST-b1 


T C F D ® 1 7 . 0 6 – U s e r ’ s G u i d e

© 2 0 1 7 C F D s u p p o r t s .r . o .

Keyword

kOmegaSST-c1 



Mandatory

10

−

no

0.09

−

no

1.44

−

no

1.92

−

no

-0.33

−

no

1

−

no

1.3

−

no

28.9

kg/mol

no

−

no

Parameter of the k-epsilon model.

kEpsilon-C1 


 Parameter of the k-epsilon model.

kEpsilon-C3 


kEpsilon-sigmak 


kEpsilon-sigmaEps 


molarWeight  Molar

 Heat capacity

1.4 ratio Cp/Cv for “totalPressure” inlet boundary condition.

Cp 

J/(kg K)

no

287.1

J/(kg K)

no

false

−

no

· ·

Gas constant.

cavitationRisk 

1004 Speficic heat capacity.

R 


weight (air = 28.9, water = 18.015).

heatCapacityRatio

6 7

Units


kEpsilon-Cmu

kEpsilon-C2 w w w . c f d s u p p o r t . c o m


 Description

Whether to evaluate cavitation properties.

6 7

6 8

Keyword


Units

Mandatory

SchnerrSauer

−

no

Pa

no

0.075

kg/s2

no

0.02308

kg/m3

no

4.273e-04

m2 /s

no

1/m3

no

m

no

−

no

−

no

101325

Pa

yes

0 0 10

m/s

yes

6 8

 Description

multiphaseCavitation 

Which model of multiphase cavitation to use, if any. Only for water machines.

multiphaseCavitation-pSat 

Saturation pressure for multiphase cavitation.

multiphaseCavitation-sigma 

Surface tension for multiphase cavitation.

multiphaseCavitation-vapourRho w w w . c f d s u p p o r t . c o m



Vapour kinematic viscosity for multiphase cavitation.

multiphaseCavitation-SchnerrSauer-n  Bubble

 Nucleation

2.0e-06

site diameter (parameter of Schnerr-Sauer multiphase cavitation model).

multiphaseCavitation-SchnerrSauer-Cc

1

Condensation rate coefficient (parameter of Schnerr-Sauer multiphase cavitation model).

multiphaseCavitation-SchnerrSauer-Cv 

1.6e+13

number density (parameter of Schnerr-Sauer multiphase cavitation model).

multiphaseCavitation-SchnerrSauer-dNuc



© 2 0 1 7 C F D s u p p o r t s .r . o .

Vapour density for multiphase cavitation.

multiphaseCavitation-vapourNu 

2300

1

Vapourisation rate coefficient (parameter of Schnerr-Sauer multiphase cavitation model).

initialPressure  Initial

condition for static pressure.

initialVelocity  Initial

condition for velocity vector (x y z components).

initialTemperature  Initial

290

condition for temperature. *) Only used in compressible calculations.

K

yes*

T C F D ® 1 7 . 0 6 – U s e r ’ s G u i d e

© 2 0 1 7 C F D s u p p o r t s .r . o .

Keyword

initialTurbulentEnergy  Initial

 Initial

Mandatory

1.5

m2 /s2

yes

1/s

yes

scaleFactor 

−

yes

−

yes

001

−

yes

3

−

yes

0

deg

no

m

no

100

condition for specific rate of dissipation of turbulent kinentic energy (omega).

0.001

Scale factor for STL files and various other metric properties.

000  Rotation axis position (any point on axis of rotation).

axis  Rotation

axis direction.

numberOfRegions  Number

of components.

featureEdgesIncludedAngle  Angle

used to extract STL edges, 0 = only boundaries.

1_wheelDiameter 

./STL

 Directory

 Hook-up

true | false

the STL files of the first component, default = true.

1_meshPath

./mesh_rotor

Path to an existing external OpenFOAM mesh. Use either “1_filePath” or “1_meshPath”.

1_componentName 

−

yes*

with STL files or path to a multi-solid STL of the first component. Can be both relative (w.r.t. TCFD file) and absolute.

1_surfaceHookUp



0


Wheel / Impeller / Rotor diameter for the first component. Used to post-process fans.

1_filePath

6 9

Units

condition for turbulent kinetic energy (k).

initialTurbulentDissipation

origin w w w . c f d s u p p o r t . c o m


 Description

rotor

Custom name for the component (used in patch names)

− − −

no

yes* no 6 9

7 0

Keyword


Units

0 0 -200

m

Mandatory

7 0

 Description

1_internalPoint

yes*

Point inside the first component (affected by scale factor). Defines the interior, where the fluid will simulated. Used only when meshing. 

1_backgroundMeshSize  Mesh size

pump_pipe_inlet  Inlet

−

no

pump_per1 pump_per2

−

no

 Rotationally

name_per1 name_per2

−

no

name_per1 name_per2

−

no

6

−

no

pump_pipe_wall pump_pipe2_wall

−

no

pump_rotor_inlet

−

no

0

−

no

−

no

coupled surfaces, in pairs. Used for segment side patches.

1_translationAMI Translationally coupled surfaces, in pairs.

1_internalAMI

patches coupled through the AMI.

1_numberOfPeriodicSegments © 2 0 1 7 C F D s u p p o r t s .r . o .

pump_pipe_outlet Outlet surface(s).

 Internal



Periodic multiplier, number of segments.



General rigid wall surface(s).

1_wall 1_2_inletInterface 

inlet to component 1 from component 2.

1_2_inletInterface-mixingPlanes  Number

of averaging planes, default=1 – if 0 then cyclicAMI is used.

1_3_outletInterface 

yes* no

1_rotationAMI



−

surface(s). Must correspond to STL files in a directory or to solids In multi-solid STL file.

1_outlet 

m

in each direction (affected by scale factor). Used only when meshing.

1_inlet w w w . c f d s u p p o r t . c o m

4.0 4.0 4.0

Outlet from component 1 to component 3.

pump_rotor_outlet

T C F D ® 1 7 . 0 6 – U s e r ’ s G u i d e

© 2 0 1 7 C F D s u p p o r t s .r . o .

Keyword

1_3_outletInterface-mixingPlanes  Number



Mandatory

1

−

no

m

no

80

Wheel / Impeller / Rotor diameter for the second component. Used to post-process fans.

2_filePath

./STL

 Directory

−

m

yes*

with STL files or path to a multi-solid STL of the second component. Can be both relative (w.r.t. TCFD file) and

2_internalPoint

0 0 -200

yes*


2_cylindricalBackgroundMesh  Background

 Mesh size

1_cylindricalBackgroundMeshWarp

0.05 0.1 0.2

−

no

0

−

no

pump_rotor_inlet

−

no

pump_rotor_outlet

−

no

pump_rotor_wall pump_pipe2_wall

−

no

surface(s).

2_outlet 

yes* no

Cylindrical mesh warp, default: 0.

2_inlet

2_wall

−

Cylindrical mesh radiuses r0 r1 r2 default: r2/4 r2/2 maxR*1.01.

 Inlet

m

no

11

Cylindrical mesh gradients g1 g2.

1_cylindricalBackgroundMeshRadii



4.0 4.0 4.0

−


1_cylindricalBackgroundMeshGrading



true | false

mesh can be cylindrical or Cartesian, default=false.

2_backgroundMeshSize



7 1

Units

of averaging planes, default=1 – if 0 then cyclicAMI is used.

2_wheelDiameter

absolute.



 Description

Outlet surface(s).


7 1

7 2

Keyword


Units

Mandatory

pump_rotor_123 pump_rotor_456

−

no

pump_rotor_hub

−

no

pump_rotor_shroud

−

no

pump_rotor_hfill

−

no

pump_rotor_sfill

−

no

pump_rotor_PS

−

no

pump_rotor_SS

−

no

pump_rotor_LE

−

no

pump_rotor_LE

−

no

pump_rotor_TE

−

no

true | false

−

no

−

no

7 2

 Description  Rigid

wall surface(s).

2_blade  Blade

surface(s).

2_hub  Hub surface(s).

2_shroud 


Shroud surface(s).

2_bladeHubFillets  Hub-fillets



Shroud-fillets surface(s).

2_bladePressureSide  Blade

pressure side surface(s).

2_bladeSuctionSide  Blade

© 2 0 1 7 C F D s u p p o r t s .r . o .

surface(s).

2_bladeShroudFillets

suction side surface(s).

2_bladeLeadingEdge  Blade

leading edge side surface(s).

2_bladeTrailingEdge  Blade

trailing edge side surface(s).

2_bladeCap  Blade

caps surface(s).

2_rotatingRegion

 If the region is rotating or not, default is false.

2_cutWater

pump_rotor_CW

T C F D ® 1 7 . 0 6 – U s e r ’ s G u i d e

© 2 0 1 7 C F D s u p p o r t s .r . o .

Keyword



Units

Mandatory

0.5

m

no

m

no

m

no

pump_rotor_hubTip

−

no

0

m

no

Cut water component(s).

2_bladeCap-clearance  Distance

between bladeCap and shroud for unshrouded impelers.

2_bladeTrailingEdge-toInterfaceDistance  Distance

list of rotating patches.

3_wheelDiameter 

1.5

between leadingEdge and inlet interface.

2_rotatingPatches 

1

between trailingEdge and outlet interface.

2_bladeLeadingEdge-toInterfaceDistance  Distance



 Description

Wheel / Impeller / Rotor diameter for the second component. Used to post-process fans.

3_filePath

./STL

 Directory

−

m

yes*

with STL files or path to a multi-solid STL of the second component. Can be both relative (w.r.t. TCFD file) and

absolute.

3_internalPoint

0 0 -200

yes*


3_backgroundMeshSize  Mesh size

 Rigid

yes*

−

no

pump_spiral_outlet

−

no

pump_spiral_wall pump_cutWater_wall

−

no

Outlet surface(s)

3_wall 7 3

pump_spiral_inlet surface(s)

3_outlet 

m


3_inlet  Inlet

111


wall surface(s)

7 3

7 4

Keyword


Units

Mandatory

1

−

no

−

no

−

no

−

no

−

no

7 4

 Description

numberOfEfficiencyProbes  How

many reports to generate (default: 1).

1_efficiencyProbe-inletPatches  Inlet

patches for the first report (default: inlet of first component). Specify patches as “:”.

1_efficiencyProbe-torquePatches 



yes

Whether to include this efficiency probe in the convergence check.

numberOfBladeToBladeViews  Number

11

no

of distinct blade-to-blade views to include in the report (default: 0).

1_bladeToBladeView-meshes

2

 Meshes

−

no

−

no

−

no

−

no

−

no

−

no

to unwrap for the first blade-to-blade view, mostly whole components or blade patches. Specify component by name or number, patch by “:”.

1_bladeToBladeView-hubs © 2 0 1 7 C F D s u p p o r t s .r . o .

3:pump_spiral_outlet

Outlet patches for the first report (default: outlet of last component).

1_efficiencyProbe-convergenceCheck 

2:pump_rotor_PS 2:pump_rotor_SS

Torque patches for the first report (default: blades of rotating comps.).

1_efficiencyProbe-outletPatches w w w . c f d s u p p o r t . c o m

1:pump_pipe_inlet

 Hub

1:pump_rotor_hub

patches needed to define the first blade-to-blade view.

1_bladeToBladeView-shrouds 

1_bladeToBladeView-field 

1:pump_rotor_shroud

Shroud patches needed to define the first blade-to-blade view.

U

Field to display on the first blade-to-blade view.

1_bladeToBladeView-heights  Distances between hub

and shroud for the first set of blade-to-blade views.

numberOfMeridionalAverages  Number

0.25 0.5 0.75 1

of distinct meridional average views to include in the report (default: 0).

T C F D ® 1 7 . 0 6 – U s e r ’ s G u i d e

© 2 0 1 7 C F D s u p p o r t s .r . o .

Keyword

1_meridionalAverage-meshes  Meshes to

Mandatory

2

−

no

−

no



−

no

−

no

−

no

−

no

−

no

−

no

−

no

−

no

−

no

−

no

p

Field to display on the first meridional average view.

additionalGraphDataFiles 

data/efficiency.dat flowRateVsEfficiency,1,2

Supplies additional data sources for report graphs.

true

 Whether to generate castellated mesh during meshing of the first component.

1_snap 

true Whether to snap the castellated mesh during meshing of the first component.

1_addLayers 

false

Whether to add layers to the snapped mesh during meshing of the first component.

1_castellate-maxGlobalCells  Maximal global

10000000

number of cells during meshing.

1_castellate-maxLocalCells  Maximal number of cells

10000000 per MPI process during meshing.

1_castellate-minRefinementCells  Minimal

 Maximal relative

1

of cell transition layers between cells of different refinement level (1 = no transition).

1_castellate-featureEdgesLevel  Level of

0.1

difference between individual processes’ cell count not triggering redistribution of the mesh.

1_castellate-nCellsBetweenLevels  Number

10


number of refined cells after a refinement iteration for termination of refinement iterations.

1_castellate-maxLoadUnbalance

7 5

Units

average for the first meridional average view. Specify component by its name or number.

1_meridionalAverage-field

1_castellatedMesh w w w . c f d s u p p o r t . c o m


 Description

0

refinement of the castellated mesh along the feature edges.

7 5

7 6

Keyword


Units

Mandatory

14

−

no

−

no

−

no

−

no

−

no

−

no

−

no

−

no

−

no

−

no

−

no

−

no

7 6

 Description

1_castellate-default-refinementSurfaces  Default minimal

and maximal refinement for all surfaces.

1_inlet-refinementSurfaces  Minimal

and maximal refinement for inlet boundaries.

1_outlet-refinementSurfaces  Minimal

 Minimal

14

and maximal refinement for blade hub fillets boundaries.

1_bladeShroudFillets-refinementSurfaces  Minimal

14

and maximal refinement for shroud boundaries.

1_bladeHubFillets-refinementSurfaces  Minimal

© 2 0 1 7 C F D s u p p o r t s .r . o .

14

and maximal refinement for hub boundaries.

1_shroud-refinementSurfaces  Minimal

14

and maximal refinement for blade boundaries.

1_hub-refinementSurfaces  Minimal

14

and maximal refinement for wall boundaries.

1_blade-refinementSurfaces  Minimal

14

and maximal refinement for outlet boundaries.

1_wall-refinementSurfaces w w w . c f d s u p p o r t . c o m

14

14

and maximal refinement for blade shroud fillets boundaries.

1_bladePressureSide-refinementSurfaces 1 4  Minimal

and maximal refinement for blade pressure side boundaries.

1_bladeSuctionSide-refinementSurfaces  Minimal

and maximal refinement for blade suction side boundaries.

1_bladeLeadingEdge-refinementSurfaces  Minimal

14 14

and maximal refinement for blade leading edge boundaries.

T C F D ® 1 7 . 0 6 – U s e r ’ s G u i d e

© 2 0 1 7 C F D s u p p o r t s .r . o .

Keyword

1_bladeTrailingEdge-refinementSurfaces  Minimal

 Minimal

Mandatory

14

−

no

−

no

1_cutWater-refinementSurfaces  Minimal

−

no

−

no

−

no

deg

no

−

no

−

no

−

no

−

no

−

no

−

no

14

and maximal refinement for blade cap boundaries.

14

and maximal refinement for cut water boundaries.

14

 Minimal and maximal refinement for cyclic AMI boundaries.

1_internalAMI-refinementSurfaces  Minimal

 Maximal feature

3

of patch smoothing iterations before finding correspondence to surface.

1_snap-tolerance  Maximum relative

 Number

2 distance for points to be attracted by surface.

30

of mesh displacement relaxation iterations.

1_snap-nRelaxIter

5

 Maximum number of

snapping relaxation iterations.

1_snap-nFeatureSnapIter  Number

30

angle that has influence on refinement.

1_snap-nSmoothPatch  Number

14

and maximal refinement for internal AMI boundaries.

1_castellate-resolveFeatureAngle

1_snap-nSolveIter

10

of feature edge snapping iterations.

1_snap-implicitFeatureSnap 7 7

Units

and maximal refinement for blade trailing edge boundaries.

1_bladeCap-refinementSurfaces

1_cyclicAMI-refinementSurfaces w w w . c f d s u p p o r t . c o m


 Description

 Detect (geometric

true

only) features by sampling the surface.


7 7

7 8

Keyword


Units

Mandatory

true

−

no

true

−

no

true

−

no

3

−

no

1.2

−

no

0.25

− (m)

no

0.05

− (m)

no

0

−

no

90

deg

no

25

−

no

−

no

−

no

7 8

 Description

1_snap-explicitFeatureSnap 

Take into consideration manually generated feature edges.

1_snap-multiRegionFeatureSnap  Detect features

between multiple surfaces.

1_layers-relativeSizes  Relative

or absolute layer thickness.

1_layers-defaultWall-nSurfaceLayers w w w . c f d s u p p o r t . c o m

 Default number

 Expansion

factor for layer mesh.

1_layers-finalLayerThickness 

Wanted thickness of the layer furthest away from the wall.

1_layers-minThickness  Minimum overall

thickness of total layers.

1_layers-nGrow  If

© 2 0 1 7 C F D s u p p o r t s .r . o .

of suface layers for a wall.

1_layers-expansionRatio

points get not extruded do nGrow layers of connected faces that also not grown.

1_featureAngle 

When not to extrude surface.

1_layers-nRelaxIter  Max

number of iterations after which relaxed meshQuality controls get used.

1_layers-nSmoothSurfaceNormals  Number

of smoothing iterations of surface normals.

1_layers-nSmoothNormals  Number

10 15

of smoothing iterations of interior mesh movement direction.

T C F D ® 1 7 . 0 6 – U s e r ’ s G u i d e

© 2 0 1 7 C F D s u p p o r t s .r . o .

Keyword

1_layers-nSmoothThickness 



Mandatory

10

−

no

0.3

−

no

0.5

−

no

90

−

no

0

−

no

−

no

deg

no

20

−

no

4

−

no

80

−

no

1E-16

m3

no

Stop layer growth on highly warped cells.

1_layers-maxThicknessToMedialRatio  Reduce

layer growth where ratio thickness to medial distance is large.

 Angle used to pick up medial axis points.

1_layers-nBufferCellsNoExtrude 

Create buffer region for new layer terminations.

1_layers-nLayerIter 

50

Overall max number of layer addition iterations.

1_quality-maxNonOrtho

65

 Maximum non-orthogonality

allowed. Set to 180 to disable.

1_quality-maxBoundarySkewness  Max

boundary skewness allowed.

1_quality-maxInternalSkewness  Max

internal skewness allowed.

1_quality-maxConcave  Max

concaveness allowed.

1_quality-minVol  Minimum pyramid volume.

1_quality-minTetQuality 7 9

Units

Smooth layer thickness over surface patches.

1_layers-maxFaceThicknessRatio

1_layers-minMedianAxisAngle w w w . c f d s u p p o r t . c o m


 Description

 Minimum

centre.


Is absolute volume of cell pyramid. Set to a sensible fraction of the smallest cell volume expected.

-1E+30

−

no

quality of the tet formed by the face-centre and variable base point minimum decomposition triangles and the cell

7 9

8 0

Keyword


Units

Mandatory

1E-13

m2

no

0.02

−

no

0.001

−

no

−

no

−

no

−

no

4

−

no

0.75

−

no

8 0

 Description

1_quality-minArea  Minimum face

area.

1_quality-minTwist  Minimum face

twist.

1_quality-minDeterminant  Minimum normalised

cell determinant. This is the determinant of all the areas of internal faces. It is a measure of how much of the outside area of the cell is to other cells. w w w . c f d s u p p o r t . c o m

1_quality-minFaceWeight  Relative

position of face in relation to cell centres (from 0 to 0.5). Orthogonal mesh corresponds to 0.05.

1_quality-minVolRatio 

-1

Per triangle normal compared to average normal.

1_quality-nSmoothScale  Number

of error distribution iterations.

1_quality-errorReduction © 2 0 1 7 C F D s u p p o r t s .r . o .

0.01

Volume ratio of neighbouring cells (from 0 to 1).

1_quality-minTriangleTwist 

0.02

 Amount

to scale back displacement at error points.

T C F D ® 1 7 . 0 6 – U s e r ’ s G u i d e

Chapter 6 TCFD® – CFD Theory & Formulas 6.1 6.1.1

Formulas for the Efficiency Evaluation Hydro Turbine Efficiency

The water turbine efficiency can be evaluated using following efficiency formula:

Mω , (6.1) Qin hin Qout hout where η denotes the efficiency, M is the torque, ω is the angular velocity, Q is the volume flow rate and h is the specific enthalpy which can be evaluated as follows: 1 h = p + ( ρg) r + ρU 2 . (6.2) 2 η waterTurbine =

−

− ·

Subscript in means averaged quantities at the inlet, whereas subscript out denotes averaged quantities at the outlet. The evaluation of turbine efficiency for different patches is also possible.

6.1.2

Pump Efficiency

The pump efficiency can be evaluated using following efficiency formula:

η pump =

Qin hin

−Q

out hout

, (6.3) Mω where η denotes the efficiency, M is the torque, ω is the angular velocity, Q is the volume flow rate and h is the specific enthalpy which can be evaluated as follows: 1 h = p + ( ρg) r + ρU 2 . (6.4) 2

− ·

Subscript in means averaged quantities at the inlet, whereas subscript out denotes averaged quantities at the outlet. The evaluation of pump efficiency for different patches is also possible. 81

82


6.1.3

Compressor Efficiency

Adiabatic efficiency. Total to Total. For compressor the following efficiency formula is used:

ηacompressor

6.1.4

  p2,tot p1,tot

T 1,tot T 2,tot,IS T 1,tot = = T 2,tot T 1,tot T 2,tot

− −

−1

κ

κ

− T

1,tot

− T

(6.5)

1,tot

Turbine Efficiency

Adiabatic efficiency. Total to Static. For steam turbine or centrifugal turbine the following efficiency formula is used:

T 2

ηaturbine = T 1,tot

6.1.5

 

− T

1,tot

−1

κ

p2

κ

p1,tot

+

c22 2cp

− T

(6.6)

1,tot

Fan Efficiency η f an =

P t P w

(6.7)

˙ 2 [W] • Pt aerodynamic power, P t = Y t m

·

• Pw • f • Yst

torque power, P w = M d ω [W]

·

compress factor, f = 1

− 0.36 · ∆ ps

static work, Y st = f

·

• Yd dynamic work, Y d =

ρ1

c22 −c21 2

∆ ps

ps1

[-]

[m2 /s2 ] [m2 /s2 ]

• Yt total work, Y t = Y st + Y d [m 2 /s2] • psi

pressure number, ψ =

• phi

flow number, φ =

• axialForce • pTotInlet

82

2·D ·∆ pt

ρ1 ·c2c

Qw A·cc

=

=

24.3·Qw

n·D 3

729.5·∆ pt

n2 ·D2 ·ρ1

[-]

[-]

axial force on rotor, F a [N] total pressure at the inlet, pt1 [Pa]

• pTotVolute

total pressure at the outlet, pt2 [Pa]

• pTotOutlet

total pressure at the wheel outlet, pt2 [Pa]



www.cfdsupport.com


[email protected]

• pInlet

83

static pressure at the inlet, ps1 [Pa]

• pVolute

static pressure at the outlet, ps2 [Pa]

• pOutlet

static pressure at the wheel outlet, ps2 [Pa]



velocity at the inlet, c 1 [m/s]

• magUInlet • magUVolute

velocity at the outlet, c 2 [m/s]

• magUOutlet

velocity at the wheel outlet, c2 [m/s]



˙ 1 [kg/s] mass flow at the inlet, m

• massFlowInlet • massFlowVolute

˙ 2 [kg/s] mass flow at the outlet, m

• massFlowOutlet

˙ 2 [kg/s] mass flow at the wheel outlet, m

• rhoInlet • rhoVolute • rhoOutlet



density at the inlet, ρ1 [kg/m3 ] density at the outlet, ρ 2 [kg/m3 ] 

density at the wheel outlet, ρ 2 [kg/m3 ]

• volumeFlowRateInlet

volumetric flow rate at the inlet, Qw1 [m 3 /s]

• volumeFlowRateVolute

volumetric flow rate at the outlet, Qw2 [m 3 /s]

• volumeFlowRateOutlet

volumetric flow rate at the wheel outlet, Qw2 [m 3 /s]

• moment

torque at wheel, M d [N m]

• totalPressureDifference • staticPressureDifference

6.2 6.2.1



·

difference in total pressure inlet-outlet, ∆ pt [Pa] difference in static pressure inlet-outlet, ∆ ps [Pa]

Turbomachinery CFD Solvers blueSolver - steady state, incompressible

Turbomachinery CFD solver for steady state, incompressible fluid flow is called blueSolver. It was gradually developed during the time from the simpleFoam solver. In any matters the blueSolver behaves the same way as any standard OpenFOAM solver. It is compatible with all OpenFOAM applications and libraries. Solver is modified to be more robust, it can use MRF method, limits for variables can be specified and many other changes have been done. ©2017 CFD support s.r.o.

www.cfdsupport.com

83

84

6.2.2


blueDyMSolver - transient, incompressible

Turbomachinery CFD solver for transient, incompressible fluid flow is called blueDyMSolver. It was gradually developed during the time from the pimpleDyMFoam solver. In any matters the blueSolver behaves the same way as any standard OpenFOAM solver. It is compatible with all OpenFOAM applications and libraries. Solver is modified to be more robust, limits for variables can be specified and many other changes have been done.

6.2.3

redSolver - steady state, compressible

Turbomachinery CFD solver for steady state, compressible fluid flow is called redSolver. It was gradually developed during the time from the rhoSimpleFoam solver. In any matters the redSolver behaves the same way as any standard OpenFOAM solver. It is compatible with all OpenFOAM applications and libraries. Solver is modified to be more robust, it can use MRF method, limits for variables can be specified and many other changes have been done.

6.2.4

redDyMSolver - transient, compressible

Turbomachinery CFD solver for transient, incompressible fluid flow is called redDyMSolver. It was gradually developed during the time from the sonicFoam solver. In any matters the redDyMSolver behaves the same way as any standard OpenFOAM solver. It is compatible with all OpenFOAM applications and libraries. Solver is modified to be more robust, limits for variables can be specified and many other changes have been done.

6.2.5

greenSolver - steady state, cavitation

Turbomachinery CFD solver for steady state, cavitating fluid flow is called greenSolver. It was gradually developed during the time from the interPhaseChangeFoam solver. In any matters the greenSolver behaves the same way as any standard OpenFOAM solver. It is compatible with all OpenFOAM applications and libraries. Solver is modified to be more robust, it can use MRF method, limits for variables can be specified and many other changes have been done.

6.2.6

greenDyMSolver - transient, cavitation

Turbomachinery CFD solver for transient, cavitating fluid flow is called greenDyMSolver. It was gradually developed during the time from the interPhaseChangeDyMFoam solver. In any matters the greenDyMSolver behaves the same way as any standard OpenFOAM solver. It is compatible with all OpenFOAM applications and libraries. Solver is modified to be more robust, limits for variables can be specified and many other changes have been done. 84

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6.2.7 6.2.7

85

Compre Compressib ssible le Mathem Mathematic atical al Model Model

The computational model solves following system of equations:

∂ρ ∂ + [ρu j ] = 0 (6.8) ∂t ∂x j ∂ ∂ (ρu ( ρui ) + [ρui u j + pδ + pδ ij τ ji ] ij ∂t ∂x j ∂ ∂ (ρe ( ρe0 ) + [ρu j e0 + u + u j p + p + q q j ui τ ij ij ] ∂t ∂x j ∂ ∂ 1 ∂ 1 (ρh) ρh) + ρu j h + q + q j ui τ ij + ρ uk uk u j + ρ uk uk p ij + ρ ∂t ∂x j 2 ∂t 2 ∂ ∂ ∂u i ∂ ∂u j ∂p (ρh ( ρh)) + [ρu j h + q + q j ] τ ij ( pu j ) + p + p ij ∂t ∂x j ∂x j ∂x j ∂x j ∂t

−

−



 

−

−

τ ij ij q j =

−

−





≡

ij ij

∂h ∂ h α −λ ∂T ≡ − ≡− ∂x ∂x j

≡ e + u 2u

e0

k k

= 0 (6.10) = 0 (6.11) = 0 (6.12)

1 ∂u i ∂u j 1 ∂u k S ij + δ ij (6.13) ij ij 2 ∂x j ∂x i 3 ∂x k µ ∂T λ C p µ C p , α , Pr (6.14) P r ∂x j C p λ C p γ , p = ρRT (6.15) C v

≡ 2µS

j

−



= 0 (6.9)

−

≡

≡

≡ ≡

,

C p

− C = R, v

h = C = C p p T ,

e = C v T (6.16)

• Mass conservation conservation 6.8 6.8 • Momentum Momentum conserva conservation tion 6.9 6.9 • Energy Energy conservat conservation ion 6.11 6.11 and and 6.12 6.12,, two options • where: where: Einstein summation is used, ∂ is partial derivative, xi is i-th Cartesian coordinate, ρ is density, ui is i-th velocity vector component, t is time, p is static pressure, τ shear stress tensor, δ ij ij is Kronecker delta, e 0 is total specific energy, µ is dynamic viscosity, S ij ij is rate-of-deformation tensor, T is static temperature, P r is Prandtl number, R specific gas constant, C p specific heat capacity (at constant pressure), C v specific specific heat capacit capacity y (at constan constantt volume volume), ), q i i-th i-th heat heat flux flux comp compon onent ent (Fourier law), λ heat conductivity coefficient. • The whole system system is closed with boundary boundary conditions. conditions. ©2017 CFD support s.r.o.

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6.2.8 6.2.8

Incompr Incompressi essible ble Mathem Mathematic atical al Model Model

Incompressible model solves the system of incompressible Navier-Stokes equations 6.17, 6.17, 6.18.

∇·u ∂ u + (u · ∇)u ∂t

= 0

= ν

2

p + g ∇ u − ∇ p +

≡≡ µρ

ν

(6.17)

(6.18)

(6.19)

• Mass conservation conservation 6.17 6.17 • Momentum Momentum conservat conservation ion 6.18 6.18 • wher where: e: Symb Symbol ol ∂ is partial derivative, u is velocity vector, t is time, p is static pressure [Pa/(kg m 3 ) = m2 s 2 ], µ is dynamic viscosity, ν is kinematic viscosity and g is gravitational acceleration vector. −

−

• The whole system system is closed with boundary boundary conditions. conditions.

6.2.9 6.2.9

Unstr Unstruct uctur ured ed Gr Grid id

The computational computational mesh data is kept in unstructured unstructured OpenFOAM OpenFOAM format. See e.g. [1 e.g. [12 2].

6.2.10 6.2.10

Finite Finite Volume olume Method Method

Solver is based on Finite Volume Method more more informati information on can be found e.g. in [2 [2], [10] 10] or [9 [9].

6.2.11 6.2.11

Three Three Dimensi Dimensional onal

All the models are solved in three dimensions, even 2D-like or 1D-like models are treated as 3D using special boundary conditions. See e.g. [12 [12]. ].

6.2.12 6.2.12

Stead St eady-S y-Stat tatee

The system of equations is considered to be steady-state, which means all the time derivativ derivatives es are equal to zero. For more details see e.g. [1]. 86

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6.2.13 6.2.13

87

Segrega Segregated ted Solver Solver

Segregated Segregated solver solver is used to compute unknown unknown variables. variables. The Finite Volume Volume Solution Method Method can either either use a segreg segregate ated d or a coupled coupled solution solution procedu procedure. re. With segregate segregated d methods an equation for a certain variable is solved for all cells, then the equation for the next variable is solved for all cells, etc. For more details see e.g. [1 [1].

6.2.14 6.2.14

Cell Cell Center Centered ed Appro Approach ach

A cell-centered approach stores the variable in all cell centers whereas a node-centered scheme stores it in the points. For more details see e.g. [3 [3].

6.2.15 6.2.15

Under Under-Relaxa -Relaxation tion

Under-Relaxation reduc reduces es solut solution ion oscil oscilla lati tions ons and and helps helps to keep keep the the comp computa utati tion on stabl stable. e. After each iteration, at each cell, a new value for variable U in in cell i is then updated using following equation:

U iNEW,USED = U iOLD + α U iNEW,PREDICTED



OLD i

− U



(6.20)

where α is under-re under-relaxa laxation tion factor factor.. The choice choice α = 1 corresponds to no underrelaxat relaxation. ion. The choice choice α < 1 is under-rela under-relaxat xation. ion. This This may slow slow down down speed of convergence but increases the stability of the computation, i.e. it decreases the possibility of divergen divergence ce or oscillations oscillations in the solution. solution. For more details see e.g. [1].

6.2.16 6.2.16

System System of Linear Linear Equation Equationss

Finite Volume Method converts the system of differential equations to the system of linear equations: A

= b · x = b

(6.21)

Such a linear algebra problem can be solved with following methods implemented in OpenFOAM: Linear system solver method:

• GAMG (Geometric-Algebraic Multi-Grid) for both symmetric and asymmetric matrices • PBiCG PBiCG (Preconditioned (Preconditioned Biconjugate Biconjugate Gradient ) for asymmetric asymmetric matrices • PCG (Precondition (Preconditioned ed Conjugate Gradient) Gradient) for symmetric matrices ©2017 CFD support s.r.o.

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• smoothSolver (solver using a smoother for both symmetric and asymmetric matrices ) • ICCG (Incomplete Cholesky preconditioned PCG solver, i.e. PBiCG with DIC )1 • BICCG (Diagonal Incomplete LU preconditioned PBiCG solver, i.e. PCG with DILU)2 Method preconditioner:

• DILU (Diagonal Incomplete LU decomposition) • DIC (Diagonal incomplete-Cholesky) for symmetric matrices • FDIC (Faster diagonal incomplete-Cholesky) for symmetric matrices • diagonal (Diagonal) • GAMG (Geometric-Algebraic Multi-Grid) • none (No preconditioning) • DICGaussSeidel, GaussSeidel, nonBlockingGaussSeidel, symGaussSeidel (for symmetric matrices) For more details see e.g. [9].

6.2.17

SIMPLE Algorithm

For solving pressure - velocity coupling the SIMPLE algorithm is used. For more details see e.g. [1].

6.2.18

Spatial Integration Numerical Scheme

Space discretization scheme is limitedLinear, which is central scheme of second order accuracy. There are 55 default OpenFOAM schemes to select:

1 2

88

• CoBlended

• LUST

• Minmod

• SFCD

• Gamma

• MUSCL

• OSPRE

• SuperBee

• Gamma01

• MUSCL01

• QUICK

• UMIST

Present for backward-compatibility Present for backward-compatibility

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• biLinearFit

• limitWith

• linear

• quadraticLinearFit

• blended

• limitedCubic

• linearFit

• quadraticLinearUpwindFit

• clippedLinear

• limitedCubic01

• linearPureUpwindFit • quadraticUpwindFit

• cubic

• limitedGamma

• linearUpwind

• cubicUpwindFit

• limitedLimitedCubic • localBlended

• downwind

• limitedLimitedLinear • localMax

• reverseLinear • skewCorrected • upwind

• filteredLinear

• limitedLinear

• localMin

• filteredLinear2

• limitedLinear01

• midPoint

• filteredLinear3

• limitedMUSCL

• outletStabilised

• vanLeer

• fixedBlended

• limitedVanLeer

• pointLinear

• vanLeer01

• harmonic

• limiterBlended

• quadraticFit

• weighted

• vanAlbada

For more details see e.g. [9], [1] or [3].

6.2.19

Temporal Integration Numerical Scheme

- none (Steady-state problem)

6.2.20

Non-Orthogonal Correctors

Pressure equation is repeated according to number of non-orthogonal correctors. This may reduce the influence of bad computational mesh. For more details see e.g. [9], [1] or [3].

6.2.21

Number of Iterations on Rotor and Stator Part

User can specify how many sub-iterations are spend on rotor part and stator part during single iteration. It is recommended to use default option: one sub-iteration on rotor part and one sub-iteration on stator part. See file fvSolution.

6.2.22

Minimal and Maximal Values Options

During the computation, especially right at its start, some unphysical oscillations of solution may appear. To make the solver more robust there may be minimal and maximal values specified for selected variables. See file fvSolution. ©2017 CFD support s.r.o.

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6.2.23

Turbulent Flow

Eight default OpenFOAM turbulence models can be used within this solver: • LamBremhorstKE

• kEpsilon

• LaunderSharmaKE

• kOmega

• RNGkEpsilon

• kOmegaSST

6.2.24

• laminar

• realizableKE

MRF (Multiple Reference Frame) Method for Rotation of Rotating Parts

For simulating of the rotation it is used Multiple Reference Frame (MRF) method. MRF adds source term (acceleration) to velocity (momentum) equations. Source term is applied on volume cells cellZone. For more details see e.g. [9].

6.2.25

Message Passing Interface (MPI)

For parallel computations there is Message Passing Interface (MPI) standard used. For more details see e.g. [13].

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6.3

91

Notes on gravitational potential and hydrostatic pressure

6.3.1

Potential of a homogeneous gravitational field

A homogeneous gravitational field is characterized by a constant vector field g , the well known gravitational acceleration. Let us consider some volume or vessel filled with an incompressible fluid of density  . The gravitational field exerts a force on the fluid. Its  is given by the following well known formula force density f

 = g f

.

(6.22)

It is a simple task to find a potential to (6.22). Let us remind, a potential (if it exists)  is defined as a certain function φ satisfying the following of some given force field F equation φ = F . (6.23)

−∇

 given by (6.22) there exists a potential, let us denote it by ϕ, We can see that to the f stating ϕ (r) = g r + C , (6.24)

− ·

3

where C

∈ R is a constant of integration

6.3.2

and r is a position vector4 .

Hydrostatic pressure

Let us consider an incompressible fluid at rest in the presence of a homogeneous gravitational field so it is supported by walls of some, possibly open, vessel. Inside a volume of the fluid there is the well known hydrostatic pressure, let us denote it by p . Assume the fluid has one free5 part of its boundary, i.e. one part of its surface forms a level, i.e. plane or its part. Let us denote by r0 a position vector6 of an arbitrary point of this plane. Hence for p holds p (r) = g (r r0) . (6.25)

· −

Notice the relation (6.25) is valid inside the volume of the fluid only. If we need to extend its domain, it is necessary to assure zero values for p outside of the volume of the fluid. For instance, this is satisfied naturally, if we consider  a constant scalar field but vanishing outside the volume of the fluid. 3

For it is the change or difference, whether finite or infinitesimal, of the potential that matters, not its actual value, we disregard such a constant unless stated explicitly. 4 defining the position of a certain point with respect to origin of a system of coordinates 5 i.e. not in contact with any wall of the vessel 6 in a given system of coordinates


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Figure 6.1: General water turbine sketch. Physical setting of a turbine casing with respect to a dam. Water levels indicated.

6.3.3

Center of mass of a surface

Consider a two dimensional surface S, choose a system of coordinates and define a position vector rS of its center of mass as following

rS

 r dS =  dS S

,

(6.26)

S

where r is a position vector of an element dS .

6.4

Water turbines - notes on calculations

Figure 6.1 represents a physical setting of a turbine casing with respect to a dam. Let us denote by h the head, i.e. the difference between heights of water levels in front of the dam and at the back of it. Vertical distance between the center of mass of the inlet surface of volute and the high water level is denoted by h In . Vertical distance between the center of mass of the outlet surface of draft tube and the low water level is denoted by hOut . Finally, vertical distance between the centres of mass of inlet and outlet surfaces is denoted by h IO . 92

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We can see there are several simple relations among quantities just defined

h + hOut = hIn + hIO h = hIn + hIO hOut h hIO = hIn hOut

−

−

−

(6.27)

(6.28)

(6.29)

To simplify calculations we usually considers water an incompressible fluid with no phase changes possible and we solve the well known equations, the conservation laws the fluid obeys. Coservation of linear momentum is expressed by the Navier-Stokes equation. In this case (incompressible fluid, steady state) it can take the form

 U

· ∇U  − ν ∆U  = − ∇ p + 1

1





f ,

(6.30)

 is a  is a velocity field, ν kinematic viscosity,  density, p pressure field and f where U force density of a gravitational field, given by (6.22). Conservation of mass is expressed by the continuity equation. In this case it takes the simple form  U = 0 , (6.31)

∇·

It remains to discuss boundary conditions for the equations mentioned above. For we usually do not know the inlet velocity field, we are about to prescribe pressure field for both inlet and outlet surface. At the inlet surface a total pressure is known and it is equal to hydrostatic one. With the use of formula (6.25) we can write

ptot,In (r) = g (r

· − r

) ,

0,H

(6.32)

where r0,H is a position vector of an arbitrary point of the high water level (plane). Since total pressure is defined as a sum of static and dynamical pressure

 2 ptot = p + 21 U

,

(6.33)

we can, by means of this definition (6.33) and formula (6.32), express p at the inlet

pIn (r) = g (r

· − r

)

0,H

1 2

−

 2(r) . U

(6.34)

At the outlet the situation is a little bit complicated. After the flow (with high total pressure) exits the draft tube it mixes with water (with low total pressure) surrounding the draft tube. We usually take simplifying steps and assume the static pressure of exiting flow equals the hydrostatic pressure of surrounding water, i.e. we write

pOut (r) = g (r

· − r

0,L

) ,

(6.35)

where r0,L is a position vector of an arbitrary point of the low water level. Described steps correspond to real physical setting. In a task like this we need to know not only the h, but even hIn (optionally hOut ), i.e. a position of the turbine with respect to the high or low water level. Quantity h IO can be obtained from the given turbine casing geometry, of course. ©2017 CFD support s.r.o.

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6.4.1


Alternative formulation

Model setting

Since equation (6.30) is independent on actual pressure field values, but only on its gradients, we can formally simplify the boundary condition at the outlet by adding a certain constant C to the right hand side of the prescription (6.35) in order to get mean value of the outlet pressure equal to zero and not to hydrostatic presure at the center of mass of the outlet surface. If we do this, we have to amend the inlet boundary condition (6.32) the same way, of course. We can find easily that the constant C has following value

C = g (r0,L

·

− r

Outlet)

=

−gh

,

Out

(6.36)

where rOutlet is a position vector of the centre of mass of the outlet surface. Hence prescription (6.35) changes to

pOut (r) = g (r

Outlet )

· − r

,

(6.37)

and prescription (6.32) to

ptot,In (r) = g (r

· − r

+ r0,L

0,H

− r

.

Outlet )

(6.38)

(6.39)

A mean value ptot,In of the total pressure at the inlet surface now gives

ptot,In =



1

S Inlet



g (r

· − r

Inlet

=

1

S Inlet

+ r0,L

0,H

·

= g (rInlet r0,H + r0,L = g(h hIO ) ,

−

−

Outlet ) dS

g r dS + g ( r0,H + r0,L

Inlet

·

− r

·− − r

− r

Outlet )

Outlet )

(6.40) (6.41)

(6.42)

g . where rInlet is a position vector of the center of mass of the inlet surface and g We can see that in this model setting there is no need to know the position of a turbine to the water level. It suffices to know h and take the measurement of hIO .

≡  

Model setting without an explicit use of g in the momentum equation

Let us take a look at the equation (6.30) as if its right hand side were known. Then we can introduce an alternative quantity, denoted by p gh , to the static pressure p −

p

gh =

−



p

− gh



= p

− g · r = p + ϕ

.

(6.43)

By means of (6.43) we can formally substitute equation (6.30) by the following one

 U

· ∇U  − ν ∆U  = − ∇ p

94

1



gh

−

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(6.44)


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for the right hand side takes the same values. This is the consequence of a fact that field (6.22) has potential and thus a change in potential energy of an arbitrary element of a fluid is not dependent on its path, but on its initial and final position only. By introducing p gh we formally drop g out from the momentum equation. However, in order to obtain the same solution as in the previous settings, it is necessary to alter the presrciption (6.38) by adding g (rOutlet rInlet ) to its right hand side7 . By doing this we obtain a new prescription, but this time for the quantity p gh −

·

p

r) gh,tot,In(

−

−

= g (r

−

· − r

+ r0,L

0,H

− r

Inlet )

.

(6.45)

(6.46)

If we calculate the mean value of (6.45), we obtain

p

1

gh,tot,In = S Inlet

−

 

Inlet

=

1

S Inlet

Inlet

= g (r0,L = gh .

·

g (r

· − r

+ r0,L

0,H

− r

Inlet ) dS

g r dS + g ( r0,H + r0,L

·

− r

·−

)

− r

Inlet )

0,H

(6.47) (6.48) (6.49)

Prescription at the outlet surface remains formally the same as (6.37), but this time for the quantity p gh p gh,Out(r) = g (r rOutlet) , (6.50) −

· −

−

and hence its mean value is zero. We can see that in this setting there is no need to know a position of a turbine with respect to the water level and there is also no need to even take the measurement of h IO . It only suffice to know h, the head.

6.4.2

Conclusion

We have seen there are two basic approaches to water turbine calculations. 1. With g in the momentum equation (a) physical setting (b) model setting 2. Without explicit g in the momentum equation Following table shows possible boundary conditions for the pressure variable 7

This term is equal to the change of the potential energy density of an element of the fluid by its passage through the turbine (from the volute inlet to the draft tube outlet).


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pressure setting g, physical g , model

g

hTP hTP hTP

inlet ghIn = fMV g(h hIO ) fMV = gh = fMV

−

outlet gh Out = 0 = 0 =

Table 6.1: Boundary conditions

We note that hTP stands for hydrostaticTotalPressure boundary condition and values listed in the Table 6.1 for this type represent values of hydrostatic pressure in the centre of mass of the inlet surface. Whereas fMV stands for fixedMeanValue boundary condition and values listed in the Table 6.1 for this type represent values of static pressure in the centre of mass of the outlet surface. We add that pressureInletVelocity boundary condition is prescribed for the inlet velocity field for all of the above settings, where the velocity magnitude is computed from the difference between total and static pressure and its direction is taken as a local normal to the inlet surface (usually planar). Also zeroGradient boundary condition is prescribed for the outlet surface for all of the above settings.

6.5 6.5.1

Interface between rotor and stator part Frozen Rotor vs. Mixing Plane

At the interface between stator and rotor part, for each variable one can prescribe either Frozen Rotor boundary condition or Mixing Plane boundary condition. Frozen Rotor maps variable directly to the neighbour patch. Mixing Plane computes the variable average first and then maps just the average value to the neighbour patch. Both approaches can be combined (each variable can have its own option). Both approaches have benefits and drawbacks to each other. Authors of this methodology recommend to prefer Mixing Plane boundary condition. 96

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Figure 6.2: Radial turbine. Example of Mixing Plane Averaging from stator region to rotor region.


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Figure 6.3: Radial turbine. Example of Frozen rotor interpolation from stator region to rotor region.

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Chapter 7 TCFD® – Notes & Recommendations 7.1

General Notes & Recommendations

1. Turbomachinery CFD input is the surface geometry and physical settings being read from Turbomachinery CFD Configuration File (*.tcfd). The configuration file can be either created manually (e.g. modifying existing tutorial), or configuration file can be even created in special graphic interface in ParaView called TCFDSource. 2. Any number of model components is allowed. 3. Each component has to be waterproof, typically inlet + wall + outlet. 4. Watch out the model dimensions, they are critical. 5. STL surface model files has to be in ASCII format. 6. Ideally, each component surface STLs should fit vertex-to-vertex. Not necessary, but safest. 7. All the interfaces between two components should overlap, or at least to fit each other very well. 8. Mesh size - the most important mesh parameter of each component is 0_backgroundMeshSize, which is a basic mesh block (cell) to be refined. Three dimensions x y z in meters (scaleFactor parameter may change the dimension). 9. If command line used - the CFD Processor has several options. Custom case name. Writing the case. Writing the mesh. Run the simulation. Write the report. See all the options: $ CFDProcessor -help . 10. Log files - are located in ./logRun/* . 99

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11. It is not suitable to have “Trailing edge fixed on outlet” of the Impeller for any CFD simulation. It is recommended, when simulate, to extend the hub and shroud a little bit.

12. Compressibility: pump and waterTurbine are always incompressible; compressor and turbine are always compressible; fan can be both compressible and incompressible.

13. rotatingPatches: If rotatingRegion is false. RotatingPatches (if any) have rotatingWallVelocity (symmetric rotation – no MRF).

14. Rotation direction has signum minus for clockwise direction (right hand rule).

15. Cavitation risk is evaluated by function object cavitation. Saturated vapour pressure is evaluated using Antoine equation (see wikipedia), coefficients are taken from NIST. Relevant entries are referenceTemperature and referencePressure. Field cavitation is saved alongside other fields, which has values either 1 (cells with pressure below saturated vapour pressure) or 0 (other cells). Statistics such as number of cavitating cells, their volume and percentage of cavitating volume from whole computational domain are printed each time step.

16. Convergence Auto Stop - if convergenceCheck is true - each simulation point run is skipped - if the total machine efficiency change is lower than 0.1% over the last X iterations. X is equal to averagingWindow value.

17. Circumferential and Meridional angle - tangent is chosen in such a way that axis, radial and tangent (in this order) form a right-handed coordinate system. U is relative velocity, Um is projection of U into meridional plane, Ur is projection of U into radial plane, Ut is projection of U into tangential plane. Meridional angle α is angle between axis and Um. It is positive, when Um points away from axis and negative when Um points toward axis. Axial circumferential angle β a , is angle between tangent and Ut. Radial circumferential angle β r is angle between tangent and Ur. It is positive when Ur points out (of the cylinder in the picture), it is negative when Ur points in. 100

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18. Cylindrical background mesh can be used. Three radii, two gradients and warping. 19. CFD Processor is capable of scheduling MPI jobs to remote machines. This can be used with OpenMPI in Linux. The keyword “hosts” in the configuration file is followed by a list of nodes (hostnames or IP addresses). Password-less SSH access to those machines must be possible and the OpenMPI package, as well as the calculation directory itself, must be accessible at the same filesystem path, e. g. through the use of a disk shared among the machines. The parameter “bindToCore” is ignored when “hosts” is used. *-clearance - non-mandatory parameter which can be used to improve robustness of meshing at clearance between bladeCap and shroud *-toInterfaceDistance - non-mandatory parameter which can be used to improve robustness of meshing at small gaps between particular part of blade and neighbouring geometry 20. Currently, there are two possible transport models: sutherland (default) and constant. If “sutherland” is used, then is it possible to set also the parameters of the ©2017 CFD support s.r.o.

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Figure 7.1: Cylindrical background mesh (here viewed along the axis) is fully specified by its length (not shown) and six more parameters. The parameter r 2 is the radius of the outer cylinder. The parameter r1 is the radius of the middle cylinder. The inner “cylinder” is cylinder only when d = r 0 , which is just a special case. Generally it is allowed d < r0 and the derived parameter w = 1 r0 /d 2 is called warp and is equal to 1 for ideally cylindrical shape and to 0 when the inner “cylinder” collapses to the dashed rectangular shape. The numbers g0 and g1 specify the mesh grading (gradual change of cell sizes).

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Sutherland model: As (default 1.512e-06) and Ts (default 120). If “constant” is used, then the parameter Pr (default 0.7 for air, 7 for water) are available. 21. There are three possible turbulence models: kOmegaSST (default), kEpsilon and laminar. The names and default values of the optional parameters of the models are: kOmegaSST-alphaK1 (0.85), kOmegaSST-alphaK2 (1.00), kOmegaSSTalphaOmega1 (0.5) kOmegaSST-alphaOmega2 (0.856), kOmegaSST-beta1 (0.075), kOmegaSST-beta2 (0.0828), kOmegaSST-betaStar (0.09), kOmegaSST-gamma1 (0.5555556), kOmegaSST-gamma2 (0.44), kOmegaSST-a1 (0.31), kOmegaSST-b1 (1.00), kOmegaSSTc1 (10.0), kOmegaSST-F3 (false); kEpsilon-Cmu (0.09), kEpsilon-C1 (1.44), kEpsilonC2 (1.92), kEpsilon-C3 (-0.33), kEpsilon-sigmak (1.00), kEpsilon-sigmaEps (1.30). 22. CFD Processor allows a straighforward extension of the built-in workflow by userdefined functions. These take form of a Python scripts and can be executed in several places along the workflow. The keyword for setting used defined functions is userDefinedFunctions and has the following syntax: userDefinedFunctions script locations [ script locations . . . ] The word script is a path (no spaces!) to the Python script to be executed. During write-out of the case is will be written to the subdirectory “scripts” of the case directory and executed from that place. The word locations is a comma-separated list (no spaces!) of execution points during the workflow, when the script is to be executed. The possible execution points are: afterWrite, beforeMeshing, afterMeshing, beforeCalculation, afterCalculation, beforeEverySpeedline, afterEverySpeedline, beforeReport, afterReport. The script can use common Python functions and also two special predefined functions SetEntry and WriteFile. E.g. SetEntry(‘system/fvSolution’, ‘SIMPLE/nNonOrthogonalCorrectors’, ‘5’) WriteFile(‘system/fvSolution’) Finally, the special predefined variable CaseDirectory contains full path to the directory with the case. 23. END.


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Chapter 8 Turbo Blade Post - graphical postprocessing Turbo Blade Post is designed for postprocessing of rotating machinery. Both radial and axial machines. Pumps, hydro (water) turbines, compressors, turbochargers, propellers and many more. Turbo Blade Post is product of company CFD Support s.r.o. (www.cfdsupport.com). It was especially created to enable an effective postprocessing of rotating machinery. Turbo Blade Post is a set of plugins for ParaView software www.paraview.org. ParaView is an open source multiple-platform application for interactive, scientific visualization. It has a client–server architecture to facilitate remote visualization of datasets, and generates level of detail (LOD) models to maintain interactive frame rates for large datasets. It is an application built on top of the Visualization Tool Kit (VTK) libraries. Where VTK is a set of libraries that provide visualization services for data, task, and pipeline parallelism, ParaView is an application designed for data parallelism on sharedmemory or distributed-memory multicomputers and clusters. It can also be run as a single-computer application. ParaView offers the possibility to extend its functionality in several directions. This encompasses modifications to the GUI, implementation of new sources (i.e. generation of predefined curves and bodies), definition of new selection functions etc. The most useful category of plugins are the Filters.

Any extension to ParaView comes in a form of a shared library (something .dll in Windows or libsomething .so in Unix-like systems). The library can be loaded into ParaView using the plugin manager. The plugin manager is accessible through Tools > Manage Plugins. All new plugins have to be loaded there and optionally set to auto-load (see fig. 8.2).

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Figure 8.1: ParaView custom filters

Figure 8.2: ParaView plugin manager

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Note — The filters tend to disappear from their categories after use. This is a feature of ParaView, which moves the last used filter menu item into Filters > Recent . That list is, however, limited. Nevertheless, all filters are alwys accessible through the Filters > Search option.

8.1

Geometry & Mesh

All following Turbo Blade Post usage examples are presented on a numerical results from a simulation of an incompressible flow in a pump. The boundary geometry of the simulated volume of the pump is shown in the figure 8.3. The meshing and calculation has been done by Turbomachinery CFD / CFD Processor using the OpenFOAM package. The resulting meshes are displayed in the figures 8.4 and 8.5. Numerical results are illustrated in the figures 8.6 and 8.7. These are classical visualisations from ParaView. Turbo Blade Post offers several new ways how to inspect the numerical data, which are presented in the following chapters.

Figure 8.3: Geometry of the Turbomachinery CFD tutorial pump used in this examples.


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Figure 8.4: Computational mesh in the rotor MRF (rotating) zone as generated by Turbomachinery CFD using the snappyHexMesh mesher.

Figure 8.5: Computational mesh in the rotor MRF (rotating) zone as generated by Turbomachinery CFD using the snappyHexMesh mesher.

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Figure 8.6: Static pressure field in the pump. The incompressible simulation has been done by Turbomachinery CFD using OpenFOAM.

Figure 8.7: Relative velocity streamlines in the rotating part (MRF zone) of the mesh. The incompressible simulation has been done by Turbomachinery CFD using OpenFOAM.


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Example: Meridional average

The aim of the first example is to meridionally average the scalar quantities in the vicinity of the blades, in the rotating (MRF) section of the fluid. Whereas the simple axial slice very often cuts a blade, the meridional average avoids the holes by displaying circumferential average of values around the axis of rotation, see figure 8.8.

Figure 8.8: Comparison between a common ParaView Slice filter (top) and Turbo Blade Post Meridional Average filter (bottom) – application on Turbomachinery CFD (OpenFOAM) calculation of incompressible flow in a pump.

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Step by step guide

Step 1 — Load the OpenFOAM case into ParaView and make sure that you included the rotating zone. Depending on the way how you loaded the OpenFOAM case you can use either the "Include Zones" check-box above the mesh/field selection frames (figure 8.9 left), or "Read Zones" check-box below to read the rotating zone (figure 8.9 right). The former way, more frequent in Linux, will add available zones at the end of the "Mesh Parts" selection list (and you need to select them manually). The latter way, more frequent in Windows, will automatically read all available zones after clicking on the "Apply" button. Choose some non-zero simulation time, select appropriate components ("Mesh parts") and fields ("Volume fields") and press "Apply". This will load the mesh. Step 2 — Meridional average can be calculated by an application of the filter Meridional Average, which is part of Turbo Blade Post . You should see the icon of the filter in the toolbar. Note that the filter is available (i.e. coloured and clickable) only when the data selected in "Pipeline browser" are of the type "Unstructured grid" (see panel "Information", section "Statistics"). If we loaded several blocks (mesh parts), we would first need to extract the appropriate mesh zone using the filter Extract block , see figure 8.10.

Either use this button, or select the filter Meridional Average in the Filters > Turbomachinery (or Filters > Alphabetical) menu, or use the search box from Filters > Search . This will add the filter into the "Pipeline browser". Step 3 — The properties of the filter Meridional Average are shown in the figure 8.11. Some of the options are advanced and can be displayed using the "Toggle advanced properties" button (wheel symbol). The setup consists of a just a few numbers: (a) rotation axis, (b) axis origin, (c) clip out radius and (d) resolution. The "resolution" is the number of points of the resulting projection in radial or axial direction, whichever is larger. A non-zero "Inner radius" is necessary if the rotation axis pierces through the computational mesh, i.e. if there is no hole along the axis. In this tutorial the rotation axis is the axis z , the origin coincides with the coordinate system origin and we choose the clip out radius to be 0.01 m, as shown in the figure. Confirm the settings by pressing the "Apply" button. A non-zero "Outer radius" can be used to clip out some unwanted parts. ©2017 CFD support s.r.o.

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Figure 8.9: Loading the OpenFOAM pump case for application of Turbo Blade Post Meridional Average. Left (OpenFOAM’s OpenFOAM reader): The MRF zone and all fields are selected. Right (ParaView’s Foam reader): All zones and fields are selected for reading.

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Figure 8.10: Extraction of a single block from a multi-block dataset using the filter Extract Block , so that the Meridional Average can be applied. In this example we are interested only in the “rotor_mrf_zone” part. If the loaded case already has a single block only, it is not necessary to extract it. However, when the ParaView’s Foam reader is used, where only reading of all mesh zones at once is possible, this step is needed.

Figure 8.11: Properties of the filter Meridional Average, part of the Turbo Blade Post postprocessing toolbox. The parameters have default values, except for the non-zero"Clip out radius". ©2017 CFD support s.r.o.

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Step 4 — Once the filter completes, it will produce a projection as in the figure 8.12. By default, it shows the distance of individual points to the nearest surface (hub, shroud, inlet or outlet). However, all scalar fields have been averaged by the filter and are available in the field selection drop-down list in the main toolbar. The figures 8.13 and 8.14 show the averaged results for static pressure and relative velocity, respectively.

Figure 8.12: Resulting projection of the geometry constructed by the Turbo Blade Post toolset ( Meridional Average filter) showing an auxiliary field, together with the original geometry and the cutting cylinder that corresponds to the chosen "Clip out radius".

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Figure 8.13: Meridional average of the static pressure for an incompressible flow in a pump constructed by Turbo Blade Post / Meridional Average. Results are from a calculation by TurbomachineryCFD using OpenFOAM.

Figure 8.14: Meridional average of relative velocity restricted to the slice for an incompressible flow in a pump. Contructed by Turbo Blade Post / Meridional Average. Results are from a calculation by TurbomachineryCFD using OpenFOAM. ©2017 CFD support s.r.o.

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8.3


Example: Blade-to-blade view

The blade-to-blade view offers a unique perspective for an inspection of the flow between the blades at a fixed relative distance between hub and shroud surfaces. In Turbo Blade Post it can be generated in two steps: First, the cylindrical mesh of the rotating zone needs to be "unwrapped" into a rectangular block. Second, the unwrapped block has to be cut at the requested distance.

Figure 8.15: Blade-to-blade view constructed by the Turbo Blade Post toolset showing static pressure for an incompressible flow in pump. Results are from a calculation by Turbomachinery CFD using OpenFOAM.

8.3.1

Step by step guide

Step 1 — Load the OpenFOAM case into ParaView and make sure that you included the rotating zone. Depending on the way how you loaded the OpenFOAM case you can use either the "Include Zones" check-box above the mesh/field selection frames (figure 8.16 left), or "Read Zones" check-box below to read the rotating zone (figure8.16 right). The former way, more frequent in Linux, will add available zones at the end of the "Mesh Parts" selection list (and you need to select them manually). The latter way, more frequent in Windows, will automatically read all available zones after clicking on the "Apply" button. Choose some non-zero simulation time, select appropriate components ("Mesh parts") and fields ("Volume fields") and press "Apply". This will load the mesh. Step 2 — The transformation from the cylinder - or disk-like rotating area (as shown in the figure 8.4 or 8.5) into the normalized rectangular block can be calculated by the filter Turbo Unwrap. You should see the icon of the filter in the toolbar. Note that the filter is available (i.e. coloured and clickable) only when the data selected in "Pipeline browser" are of the type "Multi-block Dataset" (see panel "Information", section "Statistics").

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Either use this button, or select the filter Turbo Unwrap in the Filters > Turbomachinery (or Filters > Alphabetical) menu, or use the search box from Filters > Search. This will add the filter into the "Pipeline browser". Step 3 — The basic properties of the filter Turbo Unwrap are shown in the figure 8.17 figure 8.17.. When When the advanced advanced options options are hidden, hidden, there are only a few few options options to define. define. First First of all, it is necessary to choose the internal mesh, that will be transformed, and the hub and shroud patches, which will serve as a leaders to define the transformation. After the transformation is done, hub and shroud will be perfectly flat and parallel to each other, conform conformly ly deforming deforming the mesh in between. between. If multiple multiple mesh parts are selected selected in the "Unwrap mesh" window or multiple patches are selected in "Hub" or "Shroud" windows then they will be internally merged into a single entity before proceeding. In this example the mesh is well prepared and we can just select the three items that we loaded in the first step. Step 4 — Set the direction and position of the rotating axis using the parameters "Axis" and "Origin". In our case we use z -axis, -axis, which is the default default option. Step 5 — Select the position of the breaking semiplane and cutting cylinder, see figure 8.18 ure 8.18.. In this case we have chosen the plane direction along the x-axis and the radius of the cylinder equal to 0.01 m, see figure 8.17. figure 8.17. Step 6 — Click on "Apply". "Apply". Particularly Particularly the cylinder cylinder clipping (and to less extent also the transformation of the mesh and of the vector fields) can be quite time consuming for large meshes. meshes. Some parts of the algorithm algorithm are parallelized parallelized and will automatically automatically make use of multi-core multi-core machines. When the algorithm finishes, the result will look similarly to figure 8.20. figure 8.20. The The nature of the transformation transformation is illustrated illustrated in the figures 8.18 figures 8.18– –8.21. Step 7 — Unlike the scalar quantities (like pressure) the vector fields need to be transformed, too, when the mesh transforms. This is done automatically for the cell fields U and URel. As a by-pro by-produ duct ct the the filte filterr also also produ produces ces seve several ral other othercell field fieldss that that can can be used used as an input to other filters: The local streamline streamline vectors UStream and URelStream, and the cell field URelLIC, which is particularly well suited for usage in Line Integral Convolution ("SurfaceLIC" ) representation. representation. To use these fields in filters that request point fields, it is necessary to interpolate the data from points to cells, which is done as the final


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Figure Figure 8.16: Loading Loading mesh zones zones and the hub and shroud shroud patches patches needed needed by the filter filter (OpenFOAM’ M’ss OpenFOAM OpenFOAM reader): reader): Hub and shroud patches are Turbo Unwrap. Left (OpenFOA selected, as well as the rotating zone. Right (ParaView’s Foam reader): Hub and shroud patches and all zones are selected.

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step using the filter Cell data to point data (can be found in Filters > Alphabetical). This filter has no important important settings.

Step 8 — Now all that is necessary to obtain a specific blade-to-blade view is to use a standard Slice filter (z -normal -normal)) to cut through through the block block at the requeste requested d height. height. The coordinate z = 0 corresponds to the hub patch, z = 1 corresponds to the shroud patch, z = 0.5 corresponds to the surface in the middle between hub and shroud etc. This step is shown in the figure 8.22 figure 8.22,, the resulting cut displaying pressure is the figure 8.15 figure 8.15,, or showing the SurfaceLIC representation (with settings from 8.24 from 8.24)) in the figure 8.23. figure 8.23.

Figure 8.17: Basic parameters of the filter Turbo Unwrap. ©2017 CFD support s.r.o.

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Figure 8.18: Rotating area of the simulated pump’s volume before the application of the filter Turbo Unwrap. The patches are coloured here to make them easily differentiable in the following figure 8.20. Hub patch (bottom) is in solid green, shroud patch (top) in solid orange, inflow (top) is orange wireframe and outflow (bottom) green wireframe. The figure also contains the clipping cylinder corresponding to the parameter "Clip out radius" and the cutting semiplane corresponding to the direction specified by the parameter "Break".

Figure 8.19: Detail of the inflow interface mesh structure of the pump test case before the application of Turbo Blade Post plugin Turbo Unwrap. 120

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Figure 8.20: Rotating area of the simulated pump’s volume after the application of the filter Turbo Unwrap. The hub and shroud patches are now parallel, the new z coordinate runs from hub (z = 0) to shroud z = 1, the normalized circular coordinate is transformed to x (0, 2π) and the remaining coordinate that is orthogonal to both, "along the stream", is mapped to y (0, 1). The green hub patch is now in the bottom, orange shroud on top, inflow is left and behind (not visible here) and the green outflow is in the front and to the right. The two additional sides of the block arose by cutting the mesh by a semiplane specified by the revolution axis and the parameter "Break". It is not a straight cut through the cells, rather the cells that would be split by the semiplane are removed completely.

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Figure 8.21: Detail of the inflow interface mesh structure of the pump test case after the application of Turbo Blade Post plugin Turbo Unwrap. ©2017 CFD support s.r.o.

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Figure 8.22: Construction of the blade-to-blade view from the rotor block unwrapped by Turbo Blade Post plugin Turbo Unwrap.

Figure 8.23: Blade-to-blade view from the rotor block unwrapped by Turbo Blade Post plugins showing the Line Integral Convolution (LIC) representation of the flow based on the relative velocity. The results are from a calculation by Turbomachinery CFD. 122

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Figure 8.24: Surface Line Integral Convolution setup after application of Turbo Unwrap + Cell Data To Point Data filters. The coloring is taken from the magnitude of the vector field URel, the directions and sizes from URelLIC.


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8.4


Example: Pressure around the blade

For industrial applications of the CFD simulations it is often necessary to visualize the pressure distribution around the blade, when cut at a specific height. This is a direct analogy of the pressure profiles used in aeronautics when simulating wing profiles etc. In Turbo Blade Post this can be achieved by application of a sequence of ParaView filters on the blade patches.

Figure 8.25: Input geometry (hub, shroud and blade patches) for the Turbo Blade Post / Turbo Unwrap filter for construction of the around-the-blade pressure profile.

8.4.1

Step by step guide

Step 1 — Load the rotor part of an OpenFOAM case into ParaView using the command paraFoam -region rotor. Avoid loading the whole mesh; choose only the blade walls and the hub and shroud patches. Choose some non-zero simulation time, select appropriate components ("Mesh parts") and fields ("Volume fields") and press "Apply". This will load the necessary patches, figure 8.25. Step 2 — First, the blades need to be transformed from the cylinder- or disk-like arrangement to a straight rectangular block. This is done by the filter Turbo Unwrap. You should see the icon of the filter in the toolbar. Note that the filter is available (i.e. coloured and clickable) only when the data selected in "Pipeline browser" are of the type "Multi-block Dataset" (see panel "Information", section "Statistics").

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Either use this button, or select the filter Turbo Unwrap in the Filters > Turbomachinery (or Filters > Alphabetical) menu, or use the search box from Filters > Search. This will add the filter into the "Pipeline browser". Step 3 — The basic properties of the filter Turbo Unwrap are shown in the figure 8.26. When the advanced options are hidden, there are only a few options to define. First of all, it is necessary to choose the blade wall patch, that will be transformed, and the hub and shroud patches, which will serve as a leaders to define the transformation. After the transformation is done, hub and shroud will be perfectly flat and parallel to each other, conformly deforming the mesh in between. If multiple mesh parts are selected in the "Unwrap mesh" window or multiple patches are selected in "Hub" or "Shroud" windows then they will be internally merged into a single entity before proceeding. In this example the mesh is well prepared and we can just select the three items that we loaded in the first step. Step 4 — Set the direction and position of the rotating axis using the parameters "Axis" and "Origin". In our case we use z -axis, which is the default option. Step 5 — Unlike in the case of the blade-to-blade view, when constructing the pressure profile it is mostly not necessary to specify a non-zero "Clip out radius", because the blades do not reach all the way to the axis in the middle. We will leave the parameter having its default zero value. Step 6 — Click on "Apply". The transformation should be relatively fast, because the sufrace mesh of the blades is orders of magnitude easier to process than the full volume mesh. It may be necessary to zoom in or out a little (depending on the geometry) to make the result fit to window. Outcome of this step is shown in the figure 8.27, where the blades are coloured by pressure. Step 7 — Having the blades transformed we can now cut them at a specific height (z -axis) using the filter Slice. This will result in several two-dimensional intersection contours. Step 8 — Add the filter Plot Data from Filters > Alphabetical or using Filters > Search . Unselect all fields but pressure (see figure 8.28). Above the field selection box use "Points_Y" as the "X Array Name". This will use points’ Y coordinates as the data for


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the horizontal axis. Below the field selection box use "None" as "Line Style" and "Circle" as "Marker Style". This will only show one bullet per a mesh point, making the result independent on the order of the projected points. Now press "Apply". You should obtain a similar figure to 8.28.

Figure 8.26: Settings of the Turbo Blade Post / Turbo Unwrap filter for transformation of blades of the pump.

Note — The plot will contain data from all blades. As the blades are equivalent, it doesn’t hurt the visualization. If just a single blade profile was required, it would be necessary to separate one of the contours using a pair of the Clip filters .

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Figure 8.27: Blades of a pump transformed by Turbo Blade Post – Turbo Unwrap to a straight arrangement and displaying pressure field computed by Turbomachinery CFD using OpenFOAM.


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Figure 8.28: Pressure distribution around the blade for a given height (i.e. relative distance from the hub to the shroud) constructed with the aid of the plugins of Turbo Blade Post toolset. The horizontal axis shows the transformed Y axis, which corresponds to the normalized inlet-to-outlet direction position (for given hub-to-shroud distance and angular position). The vertical axis displays the value of the pressure as computed by Turbomachinery CFD using OpenFOAM.

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Example: Blade pressure and suction side contours

Turbo Blade Post allows also an easy selection of a single blade from the full complex of all blades, which might be difficult otherwise due to a strong curvature of the blades. The method works by transforming the blade patches from their original cylinder- or disk-like arrangement to a straight arrangement just like in the previous example and by isolating the chosen blade.

8.5.1

Step by step guide

Step 1 — Load the rotor part of an OpenFOAM case into ParaView using the command paraFoam -region rotor. Avoid loading the whole mesh; choose only the blade walls and the hub and shroud patches. Choose some non-zero simulation time, select appropriate components ("Mesh parts") and fields ("Volume fields") and press "Apply". This will load the necessary patches, figure 8.25. Step 2 — First, the blades need to be transformed from the cylinder- or disk-like arrangement to a straight rectangular block. This is done by the filter Turbo Unwrap. You should see the icon of the filter in the toolbar. Note that the filter is available (i.e. coloured and clickable) only when the data selected in "Pipeline browser" are of the type "Multi-block Dataset" (see panel "Information", section "Statistics").

Either use this button, or select the filter Turbo Unwrap in the Filters > Turbomachinery (or Filters > Alphabetical) menu, or use the search box from Filters > Search. This will add the filter into the "Pipeline browser". Step 3 — The basic properties of the filter Turbo Unwrap are shown in the figure 8.26. When the advanced options are hidden, there are only a few options to define. First of all, it is necessary to choose the blade wall patch, that will be transformed, and the hub and shroud patches, which will serve as a leaders to define the transformation. After the transformation is done, hub and shroud will be perfectly flat and parallel to each other, conformly deforming the mesh in between. If multiple mesh parts are selected in the "Unwrap mesh" window or multiple patches are selected in "Hub" or "Shroud" windows then they will be internally merged into a single entity before proceeding. In this example


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the mesh is well prepared and we can just select the three items that we loaded in the first step. Step 4 — Set the direction and position of the rotating axis using the parameters "Axis" and "Origin". In our case we use z -axis, which is the default option. Step 5 — Unlike in the case of the blade-to-blade view , when constructing the pressure profile it is mostly not necessary to specify a non-zero "Clip out radius", because the blades do not reach all the way to the axis in the middle. We will leave the parameter having its default zero value. Step 6 — Click on "Apply". The transformation should be relatively fast, because the sufrace mesh of the blades is orders of magnitude easier to process than the full volume mesh. It may be necessary to zoom in or out a little (depending on the geometry) to make the result fit to window. Outcome of this step is shown in the figure 8.27, where the blades are coloured by pressure. Step 7 — Having the blades transformed we can now separate the chosen blade from the rest. This is done by the filter Clip. Adding the Clip filter will provide the user with an interactive positioning tool consisting of a ball in the origin, clipping plane and its normal. Use the ball to position the plane. Use the axis to orient the plane; see figure 8.29. Once you have placed the clipping plane to one side of the chosen blade so that it doesn’t intersect any blade, click apply. Step 8 — Repeat Step 7 appending another Clip filter to isolate the chosen blade also from the other side. You may need to check the "Inside Out" option in the settings of the filter Clip. Step 9 — Append the filter Contour . In the drop-down list "Contour By" select the pressure field. Use the red cross button to erase suggested contour values (right bottom of the box "Value Range") and then press grid button (right top) to populate the list of contour values by equidistant values covering the whole pressure range. Do not modify the suggested minimal ("From") and maximal ("To") values, and use e.g. 20 samples ("Steps"). See the figure 8.30. Step 10 — Pressing "Apply" will calculate the contour data and display the contours, hiding the blade geometry. Click on the eye symbol in "Pipeline Browser" to show the blade again. The results are in the figure 8.31.

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Figure 8.29: Interaction with the interactive Clip manipulator when separating a single blade of a pump transformed by Turbo Blade Post / Turbo Unwrap filter. The blades are colored by static pressure calculated by Turbomachinery CFD using OpenFOAM.


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Figure 8.30: Settings of the filter Contour applied on a isolated pump blade transformed by Turbo Blade Post / Turbo Unwrap filter.

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Figure 8.31: Static pressure field and contours on an isolated blade transformed by Turbo Blade Post / Turbo Unwrap filter. The pressure data have been calculated by Turbomachinery CFD using OpenFOAM. Left is the pressure side, right the suction side of the blade.


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8.6


Meridional Average filter – details

The filter Meridional Average creates a geometrical slice by a plane containing the rotation axis and circumferential averages all the field data onto this slice. The slice ignores blades; there are never holes in the slice.

8.6.1

Input parameters

Figure 8.32: Turbo Blade Post; Filter properties.

Axis and its origin

This input specifies the position and direction of the rotation axis around which the rotor region is placed. Inner radius

For best results, the rotor region should be donut-shaped, i.e., there should be a hole running through its centre. Only for such shapes the slice contour is well defined. If there is no hole in the middle, this option allows specifying a positive radius of a hole to drill before applying the filter. Outer radius

This option allows specifying a positive radius to clip out some unwanted parts at the periphery. Resolution

This parameter controls the number of sampling faces in the slice. In the slice there will be approximately N faces in the axial direction. The faces are squares and their number in the radial direction is calculated automatically. 134

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Debug output

When "Debug output" is checked, then the filter produces some additional output in the form of txt files in the workking directory. These files can be used to explore the internal mechanisms particularly when contructing the projected boundary contour.

8.6.2

Averaging

At the moment only the following quantities are sampled: the pressure p , the absolute velocity U (no circumferential component), the relative velocityURel (no circumferential component), the absolute velocity magnitude magU and the relative velocity magnitude magURel.


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8.7


Turbo Unwrap filter – details

The filter Turbo Unwrap transforms the rotor region into a box according to a rather complicated set of rules. The purpose is to allow slicing the computational mesh and blades in the fixed relative distance between the hub and shroud patches. The filter can be applied to the whole computational mesh or to its individual parts (clips of e.g. only the blades). The unwrapping transformation is guided by hub and shroud patches.

8.7.1

Input parameters

Input mesh

The input mesh is one or more mesh parts that are to be "unwrapped" by the filter. Most often this will be either the internal mesh or the blade patch(es). Hub and shroud patches

Knowledge of hub and shroud profile is crucial for the transformation algorithm, because the aim of the transformation is to flatten both these patches. This selection box enables user to select both patches. Axis and its origin

This input specifies the position and direction of the rota- Figure 8.33: Turbo Blade tion axis around which the rotor region is placed. Post; Advanced Turbo Unwrap filter properties. Break

To unwrap the mesh, it is necessary to break it somewhere. This option allows specification of a direction, where the cut will occur. Clip out radius

For best results, the rotor region should be donut-shaped, i.e., there should be a hole running through its centre. Only for such shapes the unwrapping into a box is well defined. If there is no hole in the middle, this option allows specifying a positive radius of a hole to drill before unwrapping. 136

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Clipped boundary is hub

The boundary of the mesh that is newly created by the drilling (specifying non-zero "Clip out radius") can be considered to belong either to the hub or to the inlet/outlet interface. The default is to assign the new boundary to the hub patch. If unselected, the new boundary will be assumed to belong to the inlet/outlet interface. Advanced parameters

The remaining parameters are in the advanced section and can be shown by clicking on the button with a wheel sign next to the search field in the panel Properties. The number parameters "Resolution", "Tolerance" and "Iterations" are internal control parameters that influence precision and speed of the filter. "Resolution" is a approximately the number of control points along the hub and shroud patches. Raising the number of control points can increase the resolution of the approximated patches. "Tolerance" is proportional to the allowed absolute error in determination of point’s transformed coordinates (m,t,ζ ). The number should generally be smaller than the typical distance between two points in the original mesh. "Iterations" is the iteration limit set for determination of the transformed coordinates. It should not be necessary to raise the default value, unless an extremely fine mesh is being transformed. The field "Extension Points" is only used when "Snap internal points" is unchecked. It determines which sampled points of the boundary patches are used to extrapolate the patches. The number must be and integer greater than zero. If "1" is given, then only the tail of each patch is used to extrapolate their direction. If larger number is given, then the extrapolation runs in a more averaged direction. If "Snap internal points" is checked, no extrapolation is done and points outside the area bounded by hub and shroud are simply left with some extremal m-coordinate. The check box "Remove split cells" (default: on) determines whether the cells that are split by unwrapping are to be removed or kept. Removing these cells allowsParaView to display the unwrapped mesh correctly; otherwise it looks as if there was no internal mesh. However, for special meshes this leads to a crash. In such cases, unchecking is an option. The option "Normalize patches" makes sure that the transformed hub and shroud patches will be of unit size in the ξ (i.e. z ) direction. This allows easy construction of the blade-to-blade view , but it may not be desired for the overall view. If this option is unchecked, the hub will still be normalized to unit size, but the transformed shroud will keep its ratio with respect to the hub. Finally, the "Debug output" option produces additional text information as a txt files in the working directory, which can be used to explore internal mechanisms of the filter, particularly the construction of the m-ξ ( y -z ) contour which is then used to transform the whole mesh. ©2017 CFD support s.r.o.

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8.7.2

Usage

The usage of the filter is similar to other filters with one small difference: Because it allows (and requires) selection of different parts of the multi-part mesh, it is necessary to load all needed parts of the mesh, not just the internal mesh. The figure 8.34 demonstrates a typical selection of OpenFOAM case mesh and patches for the Turbo Unwrap filter.

Figure 8.34: Turbo Blade Post; Selection of multiple parts of the mesh. The filter will transform the cylinder-like mesh into a box. The meaning of its new ζ = dimensions is described in the table 8.1. In brief it can be said that the boundary z 0 is the hub patch, the boundary z ζ = 1 is the shroud patch, the boundary x m = 0 is the one of inlet and outlet interfaces that is lower on the rotation axis and the boundary x m = 1 is the other one (higher on rotation axis). The boundaries on minimal and t coordinates are only artificial and were originally connected to each other. maximal y The filter transforms only the cell data, not point data, so it may be necessary to apply the filter Cell data to point data afterwards to regain access to the point fields (which are necessary for usage of e.g. the Glyph filter). 

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Mapped to

Range

Meaning

m t ζ

x y z

(0, 1) Distance along the hub/shroud/streamline. (0, 2π) Circumferential angle. (0, 1) Distance from the hub; the "span".

Table 8.1: Coordinates of the "unwrapped" mesh. The coordinate m is relative to the full length of the hub/shroud/streamline. The coordinate ζ is relative to the full local distance between hub and shroud. The filter passes all cell data without change except for the vector fields U and URel, (m,t,ζ ). Besides which are transformed into the new coordinate system (x , y , z ) these two vector fields Turbo Unwrap also creates several additional vector fields, namely UStream and URelStream which should be used to construct streamlines in the transformed mesh and URelLIC, which should be used as an input for the Surface Line Integral 

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Convolution (SurfaceLIC) integrator when displaying realtive velocity using SurfaceLIC representation.


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Index AS Sutherland transport, 29 C p specific heat capacity, 29, 85 C v specific heat capacity, 85 P r Prandtl number, 29, 85 R specific gas constant, 85 S ij rate of deformation tensor, 85 T static temperature, 85 T S Sutherland transport, 29 δ ij Kronecker delta, 85 γ Heat capacity ratio, 29, 31 λ heat conductivity coefficient, 85 µ dynamic viscosity, 29, 85, 86 ν kinematic viscosity, 86 ∂ partial derivative, 85, 86 ρ density, 29, 85 τ shear stress tensor, 85 e0 total specific energy, 85 g gravitational acceleration, 86 p static pressure, 85, 86 q i i-th heat flux component, 85 t time, 85, 86 u velocity vector, 86 ui i-th velocity vector component, 85 xi i-th Cartesian coordinate, 85

blade-to-blade view, 116, 119, 130, 137 bladeCap, 40 bladeHubFillets, 40 bladeLeadingEdge, 40 bladePressureSide, 40 bladeShroudFillets, 40 bladeSuctionSide, 40 bladeTrailingEdge, 40 Castellated mesh, 41 cavitation, 27 Cavitation risk, 27 Multiphase cavitation, 27 Schnerr-Sauer model, 27 Cavitation risk, 26 Cell data to point data, 119, 138 cell-centered, 87 Cells between levels, 44 cellZone, 90 CFD Processor, 16, 24–26, 31, 34 circumferential angle, 31 Clip filter, 126, 130 Clip out radius, 113, 114, 125, 130, 137 Component name, 40 Compressible, 26 constant transport, 27 Contour, 130 Convergence check, 30, 35 cutWater, 40 cyclicAMI, 39 Cylindrical grading, 41 Cylindrical mesh, 41 Cylindrical radii, 41

Add layers, 45 Additional data files, 47 Averaging window, 46 Axis, 25, 117, 125, 130 Background mesh size, 25, 41 Bind to core, 35 blade, 40 Blade to blade views, 47 140

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Cylindrical warp, 41

License.dat, 21 License.key, 21 linear solver diagonal, 88 diagonalSolver, 88 DIC, 88 DILU, 88 FDIC, 88 GAMG, 88 none, 88 PBiCG, 88 smoothSolver, 88 BICCG, 88 localhost, 34

Debug output, 137 density, 29 Directed mass flow rate, 31 Directed volumetric flow rate, 31 Directory with STL files, 38 Dynamic viscosity, 26, 29 Efficiency probes, 47 Einstein summation, 85 empty, 39 Extension Points, 137 External OpenFOAM mesh, 39 Extract block, 111 Feature edges included angle, 26 Finite Volume Method, 86 Fluid name, 26 Frozen rotor, 96 fvSolution, 89 Glyph, 138 Gravitational acceleration, 26 Heat capacity, 27 Heat capacity ratio, 29, 31 Hosts, 34 hub, 40 Information, 116, 124, 129 Initial pressure, 37 Initial temperature, 38 Initial turbulent dissipation rate, 38 Initial turbulent energy, 38 Initial velocity, 37 inlet, 39 inletInterface, 39 Inner radius, 111 Internal point, 25, 41 internalAMI, 39 Iterations, 137 Kinematic viscosity, 26 ©2017 CFD support s.r.o.

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Machine type, 24 Mass flow rate, 31 Max global cells, 44 Max load unbalance, 44 Max local cells, 44 Max pressure, 33 Maximal density, 35 Maximal pressure, 35 Maximal temperature, 35 Maximal velocity, 35 Meridion average, 112 meridional angle, 31 Meridional average, 16, 47, 110, 111, 134 Mesh Parts, 129 Mesh parts, 111, 116, 124 Message Passing Interface, 34 Min refinement, 44 Minimal density, 35 Minimal pressure, 35 Minimal temperature, 35 Mixing plane, 40, 96 Molar weight, 27, 29 MPI, 34, 90 MRF, 108 MRF zone, 109 Multi-block Dataset, 116, 129

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Multi-block dataset, 124 Multi-solid STL file, 39 Multiple Reference Frame, 90 Navier-Stokes equations, 86 No. periodic segments, 40 non-orthogonal correctors, 37, 89 Normalize patches, 137 Numerical order, 35 Origin, 25, 117, 125, 130 Outer radius, 111 outlet, 39 Outlet vent, 33 outletInterface, 39 ParaView, 15, 18, 34, 129, 137 ParaView filter, 24 ParaView source, 24 Pipeline Browser, 22–24 Pipeline browser, 111, 117, 124, 125, 129, 130 Plot Data, 125 Point iterations, 30 Prandtl number, 29 pressure - velocity coupling, 88 Processors, 34 Properties panel, 23 Reference density, 26 Reference pressure, 27 Reference temperature, 27 Relaxation, 33 Remove split cells, 137 RenderView, 24 Resistance, 33 Resolution, 137 resolution, 111 Resolve feature angle, 44 Rotating component, 40 Rotation speed, 30 rotationAMI, 39 142

Scale factor, 25 scheme divergence scheme biLinearFit, 88 blended, 88 clippedLinear, 88 CoBlended, 88 cubic, 88 filteredLinear, 88 filteredLinear2, 88 filteredLinear3, 88 fixedBlended, 88 Gamma, 88 Gamma01, 88 harmonic, 88 limitedCubic, 88 limitedCubic01, 88 limitedGamma, 88 limitedLimitedCubic, 88 limitedLimitedLinear, 88 limitedLinear, 88 limitedLinear01, 88 limitedMUSCL, 88 limitedVanLeer, 88 limiterBlended, 88 limitWith, 88 linear, 88 linearFit, 88 linearPureUpwindFit, 88 linearUpwind, 88 localBlended, 88 localMax, 88 localMin, 88 LUST, 88 midPoint, 88 Minmod, 88 MUSCL, 88 MUSCL01, 88 OSPRE, 88 outletStabilised, 88 pointLinear, 88

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quadraticFit, 88 quadraticLinearFit, 88 quadraticLinearUpwindFit, 88 quadraticUpwindFit, 88 QUICK, 88 reverseLinear, 88 SFCD, 88 skewCorrected, 88 SuperBee, 88 UMIST, 88 upwind, 88 vanAlbada, 88 vanLeer, 88 vanLeer01, 88 weighted, 88 semi transient (AMI), 34 semi transient (MXP), 34 SetEntry, 48 Settings, 22 Setup file, 24 shroud, 40 SIMPLE algorithm, 88 Slice filter, 119 Snap internal points, 137 Snap mesh, 44 Snapshot interval, 46 solver blueDyMSolver, 84 blueSolver, 83 greenDyMSolver, 84 greenSolver, 84 interPhaseChangeDyMFoam, 84 interPhaseChangeFoam, 84 pimpleDyMFoam, 84 redDyMSolver, 84 redSolver, 84 rhoSimpleFoam, 84 simpleFoam, 83 sonicFoam, 84 Specific heat capacity, 29 Speedline points, 30 ©2017 CFD support s.r.o.

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Speedlines, 30 Statistics, 116, 124, 129 steady-state, 86 Surface hook-up, 40 SurfaceLIC, 117, 139 Sutherland transport, 27 AS , 29 T S , 29 symmetry, 39 TCFDManager, 15, 22, 24 TCFDSource, 15, 23, 24, 27 Time management, 34 Toggle advanced properties, 23, 111 Tolerance, 137 Total pressure, 31 Total temperature, 31 transient, 34 Transient revolutions, 34 Transient source, 34 Transient times, 34 Transient window, 46 Transport model, 27 Turbo Blade Post, 16, 124, 129 Turbo Unwrap, 16, 116, 117, 124, 125, 129, 138 turbulence model, 27 kEpsilon, 27, 90 kOmega, 90 kOmegaSST, 27, 90 LamBremhorstKE, 90 laminar, 27, 90 LaunderGibsonRSTM, 90 LaunderSharmaKE, 90 realizableKE, 90 RNGkEpsilon, 90 Turbulence settings, 27 Turbulent dissipation, 31 Turbulent energy intensity, 31 Under-Relaxation, 87 under-relaxation factors, 37

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Unstructured grid, 111 Unwrap mesh, 117, 125, 129 Use fluid defaults, 26 Value Range, 130 Volume fields, 111, 116, 124, 129 Volumetric flow rate, 31 wall, 40 wallSlip, 40 Wheel diameter, 25, 41 WriteFile, 48

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Bibliography [1] H. Versteeg, W. Malalasekera, An Introduction to Computational Fluid Dynamics: The Finite Volume Method (2nd Edition), (Feb 26, 2007) [2] LeVeque R. J., Numerical Methods for Conservation Laws Birkhauser Verlag, 1990 [3] H. Lomax, David W. Zingg, Thomas Pulliam, Fundamentals of Computational Fluid Dynamics, 2001 [4] Dvoˇrák R., Kozel K., Matematické modelovaní v aerodynamice Vydavatelství ˇ CVUT, 1996. [5] Schnerr G. H. And Sauer J., Physical and Numerical Modeling of Unsteady Cavitation Dynamics, Proc. 4th International Conference on Multiphase Flow, New Orleans, U.S.A., 2001. [6] Schiavello B., Visser F., Pump Cavitation - Various NPSHR Criteria, NPSHA Margins, and Impeller Life Expectancy, Proc. of the twenty-fifth INTERNATIONAL PUMP USERS SYMPOSIUM, 2009 [7] CFD-online web pages: Navier-Stokes equations (http://www.cfd-online.com/Wiki/Navier-Stokes_equations , date: 30. 1. 2014). [8] Wilcox D.C., Turbulence Modeling for CFD , DCW Industries [9] OpenFOAM web pages: OpenFOAM Documentation (http://www.openfoam.org/docs/ , date: 30. 1. 2014). [10] Wikipedia web pages: Finite Volume Method (http://en.wikipedia.org/wiki/Finite-volume_method , date: 30. 1. 2014). [11] NASA web pages: Isentropic Flow (http://www.grc.nasa.gov/WWW/BGH/isentrop.html , date: 30. 1. 2014). [12] OpenFOAM web pages: OpenFOAM mesh description (http://www.openfoam.org/docs/user/mesh-description.php , date: 30. 1. 2014). 145

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