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FLUENT - Laminar Pipe Flow - Problem Specification Added by Steve Weidner , Weidner , last edited by Benjamin J Mullen on Mullen on Apr 27, 2011 17:58

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Autho Author: r: Rajesh Rajesh Bhaskaran Bhaskaran,, John John Singleton Singleton,, Corne Cornellll Univer University sity

Problem Specification 1. Pre-Analysis & Start-Up 2. Geometry 3. Mesh 4. Setup Setup (Physics) 5. Solution Solution 6. Results 7. Verification & Validation Exercises

Problem Specification

Consider fluid flowing through a circular pipe of constant radius as illustrated above. The pipe diameter D = 0.2 m and length L = 8 m. The inlet velocity Ū z = 1 m/s. Consider the velocity to be constant over the inlet cross-section. The fluid exhausts into the ambient atmosphere which is at a pressure of 1 atm. Take density ρ

=

1 3 and k coefficient g / m of viscosity µ

=

2- 3k xg / 1( The m 0 e s ) . Th

Reynolds number R ebased on the the pipe di ameter is

where Ū z is the average velocity at the inlet, which is 1 m/s in this case. Solve this problem using FLUENT via ANSYS Workbench. Plot the centerline velocity, wall skin-friction coefficient, and velocity profile at the outlet. Validate your results. Note: The values values used for fo r the inlet velocity and flow propertie pro perties s are chosen for convenience rather than to reflect reali ty. The The key parameter value value to focus fo cus on is the Reynolds Reynolds number. Go to Step 1: Pre-Analysis & Start-up See and rate the complete Learning Module Go to all FLUENT Learning Modules

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FLUENT - Laminar Pipe Flow - Pre-Analysis & Start-Up Added by Steve Weidner , Weidner , last edited by Benjamin J Mullen on Mullen on Feb 08, 2012 23:31

Labels: None

Autho Author: r: Rajesh Rajesh Bhaskaran Bhaskaran,, John John Singleton Singleton,, Corne Cornellll Univer University sity Problem Specification

1. Pre-Analysis & Start-Up 2. Geometry 3. Mesh 4. Setup Setup (Physics) 5. Solution Solution 6. Results 7. Verification & Validation Exercises

Step 1: Pre-Analysis & Start-up Preliminary Analysis We expect the viscous viscous boundary layer to grow along the pipe starting at the inlet. It will eventually grow to fill the pipe completely (provided that the pipe is long enough). When this happens, the flow becomes fully-developed and there is no variation of the velocity prof ile ile in the axial direction, d irection, x (see (see figure below). One can obtain a clos ed-form solution solution to the governing go verning equations i n the fullyfullydeveloped region. regi on. You You should have have seen see n this this in the I n t r o d u c t i o n

t course. o F We l uwilli compare d M the e numerical c h a n i c

results in the fully-developed region with the corresponding analytical results. So it's a good idea for you to go back to your textbook in the Intro Intro course and review the fully-developed flow analysis. What values would you expect expect for fo r the centerline velocity and the friction fric tion factor in the fully-developed region based on the analytical solution? What is the solution for the velocity profile?

We'll create the geometry and mesh in ANSYS 12.1 which is the preprocessor for FLUENT, and then read the mesh into FLUENT and solve for the flow solution.

Start ANSYS FLUENT Prior to opening ANSYS, create a folder called p i pin aeconvenient location. We'll use this as the working folder in which files created during the session will be stored. For this simulation Fluent will be run within the ANSYS Workbench Interface. Start ANSYS workbench: S t a r t >

A l l

P r o g r a m s >

A n s y s

1 2 . 1 >

W o r k b e n c h

The The following fi gure shows the workbench window.

https://confluence.cornell.edu/pages/viewpage.action?pageId=85624043

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FLUENT - Laminar Pip Pi pe Flow - Pre-Analysis & Start-Up - Simulation - Confluence

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Higher Resolution Image

Management Management of Screen Real Estate This tutorial is specially configured, so the user can have both the tutorial and ANSYS open at the same time as shown below. It will be benefici be neficial al to have both ANSYS and your internet browser di splayed on your monitor simultan si multaneously. eously. Your Your internet browser should consume approximately one third of the screen width while ANSYS should take the other two thirds as shown below.

Click Here for Higher Resolution Resolution If the monitor you are using is insufficient in size, you can press the A land t T a keys b simultaneously to toggle between be tween ANSYS and your internet browser. Go to Step 2: Geometry See and rate the complete Learning Module Go to all FLUENT Learning Modules

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License

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FLUENT - Laminar Pipe Flow - Geometry Added by Steve Weidner , last edited by Benjamin J Mullen on Feb 08, 2012 23:19

Labels: None

Author: Rajesh Bhaskaran, John Singleton, Cornell University Problem Specification 1. Pre-analysis & Start-Up

2. Geometry 3. Mesh 4. Setup (Physics) 5. Solution 6. Results 7. Verification & Validation Exercises

Step 2: Geometry

Care to skip the geometry and meshing steps? README If you would prefer to skip the geometry and mesh steps, then you can download the necessary files here. Download the "zip" file, then extract the files to your working directory. In order to load the necessary files, go to the W o r k b e n c h

,Pthen r (o Cj el ic ct k )P a Fg i el e

>

O p e .nLastly, > click " here to p i pskip e _ l a

ahead to Step 4 of the tutorial.

Saving It would be of best interest, to save the project at this point. Click on the "Save As.." button, the W o r k b e n c h

, which is located on the top of

.PSave r othej project e c as t "LaminarPipeFlow" P a g e in your working directory. When you save in ANSYS a file

and a folder will be created. For instance if you save as "LaminarPipeFlow", a "LaminarPipeFlow" file and a folder called "LaminarPipeFlow_files" will appear. In order to reopen the ANSYS files in the future you will need both the ".wbpj" file and the folder. If you do not have BOTH, you will not be able to access your project.

Fluid Flow(FLUENT) Project Selection On the left hand side of the workbench window, you will see a toolbox full of various analysis systems. To the right, you see an empty work space. This is the place where you will organize your project. At the bottom of the window, you see messages from ANSYS. Left click (and hold) on F l u i d

F l o w, and( drag F L theU iconEinto N the T empty ) space in the P r o j e c t

.SYour c ANSYS h e m

window should now look comparable to the image below.

https://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Laminar+Pipe+Flow+-+Geometry

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Since we selected Fluid Flow(FLUENT), each cell of the system corresponds to a step in the process of performing CFD analysis using FLUENT. Rename the project to Laminar Pipe. We will work through each step from top down to obtain the solution to our problem.

Analysis Type In the P r o j e c t

S of the c h Workbench e m a window, t i c right click on G e o m and e tselect r y P r o p e, as r shown t i ebelow. s

The properties menu will then appear to the right of the Workbench window. Under A d v a n c e

change G e o ,m e t the r y

A n a l y s to i 2D s asTshown y p inethe image below.


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Launch Design Modeler In the P r o j e c t

,Sdouble c h click e m on aG te i oc m toe start t rpreparing y the geometry.

At this point, a new window, ANSYS Design Modeler will be opened. You will be asked to select desired length unit. Use the default meter unit and click O K .

Creating a Sketch Start by creating a sketch on the X Y P l. Under a n T e r e e V i e. This w will bring up the S k e t c h i n g .

O, select X u t l iY n Pe l, then a nclick e on S k e t cright h before i n g D e t a

T o o l b o x e s

Click Here for Select Sketching Toolboxes Demo Click on the + Z axis on the bottom right corner of the G r a p window h i c toshave a normal look of the XY Plane. Click Here for Select Normal View Demo In the Sketching toolboxes, select R e c t a. InnthegGl re a p window, h i c create s a rough Rectangle by clicking once on the origin and then by clicking once somewhere in the positive XY plane. (Make sure that you see a letter P at the origin before you click. The P implies that the cursor is directly over a point of intersection.) At this point you should have something comparable to the image below.


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Dimensions At this point the rectangle will be properly dimensioned. Under S k e t c h i n g , select T o Do i l mb eo nx tab, se isuse o the n default s dimensioning tools. Dimension the geometry as shown in the following image.

Click Here for Higher Resolution Under the D e t a i l table s (located V i e inwthe lower left corner), set V1=0.1m and set H2=8m, as shown in the image below.

Click Here for Higher Resolution

Surface Body Creation In order to create the surface body, first ( C l i c k

) C o n c e p t

>

S as shown u r f inathec image e below. F r o m

This will create a new surface S u r f a c . Under e S DK e 1 t a i l , select s VS i k e e wt as c Bh a1 s e

S k

O and b then j e under c t Surface s

body select the thickness to 0.1m and click A p p. Finally l y click G e n e tor generate a t e the surface. At this point, you can close the D e s i g n W o r k b e n c h

.P r o j e c t

and M go o back d e tol W e ro r k b e n c h

.PSave r oyour j work e c thus t far P inatheg e

P a g e

Go to Step 3: Mesh See and rate the complete Learning Module Go to all FLUENT Learning Modules


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FLUENT - Laminar Pipe Flow - Mesh Added by Steve Weidner , last edited by Benjamin J Mullen on Feb 08, 2012 23:16

Labels: None

Author: Rajesh Bhaskaran, John Singleton, Cornell University Problem Specification 1. Pre-Analysis & Start-Up 2. Geometry

3. Mesh 4. Setup (Physics) 5. Solution 6. Results 7. Verification & Validation Exercises

Step 3: Mesh In this section the geometry will be meshed with 500 elements. That is, the pipe will be divided into 100 elements in the axial direction and 5 elements in the radial direction.

Launch Mesher In order to begin the meshing process, go to the W o r k b e n c h

,Pthen r (o Dj e o cu tb l Pe a gC. el i c k )

M e

Default Mesh In this section the default mesh will be generated. This can be carried out two ways. The first way is to ( R i g h t

C l i c k

G e n e r a t, as e shown M in e the s image h below.

The second way in which the default mesh can be generated is to ( C l i c k ) https://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Laminar+Pipe+Flow+-+Mesh

M e s h

>as can G be e seen n ebelow. r a t e 9 / 40


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Either method should give you the same results. The default mesh that you generate should look comparable to the image below.

Note that in Workbench there is generally at least two ways to implement actions as has been shown above. For, simplicity's sake the "menu" method of implementing actions will be solely used for the rest of the tutorial.

Mapped Face Meshing As can be seen above, the default mesh has irregular elements. We are interested in creating a grid style of mesh that can be mapped to a rectangular domain. This meshing style is called M a p p e d ( C l i c k )

M e s h

Now, the M a p p e d

C o n t r o l as can > beMseen a below. p p e d

F a .cIn e orderM to incorporate e s h i this n meshing g style F a c e

M e s h i n g

F a c stillemustMbe eapplied s h toi the n pipe g geometry. In order to do so, first click on the pipe body which

should then highlight green. Next, ( C l i c k in ) theAD pe pt la yi l s

o f

M a p table, p e as d shown F abelow. c e

M e s h

This process is shown here Now, generate the mesh by using either method from the "Default Mesh" section above. You should obtain a mesh comparable to the following image.

Edge Sizing The desired mesh has specific number of divisions along the radial and the axial direction. In order to obtain the specified number of divisions E d g e

S must i be z used. i n gThe divisions along the axial direction will be specified first. Now, an E d g e

https://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Laminar+Pipe+Flow+-+Mesh

S needs i ztoi 10 / 40


be inserted. First, ( C l i c k )

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M e s h

as C shown o n below. t r o l

>

S i z i n g

Now, the geometry and the number of divisions need to be specified. First ( C l i c k )

E d g e , S . Then e l hold e c down t i o

the "Control" button and then click the bottom and top edge of the rectangle. Both sides should highlight green. Next, hit A p punder l y the D e t a i l s

table o fas shown S i z below. i n g

Now, change T y pto N e u m b e r

Then, set N u m b e r

o f as shown D i v in the i simage i o below. n s

o f to 100 D as i shown v i s below. i o n s

At this point, the edge sizing in the the radial direction will be specified. Follow the same procedure as for the edge sizing in the axial direction, except select the left and right side instead of the top and bottom and set the number of division to 5. Then, generate the mesh by using either method from the "Default Mesh" section above. You should obtain the following mesh.

As it turns out, in the mesh above there are 540 elements, when there should be only 500. Mesh statistics can be found by clicking on M e sin the h Tree and then by expanding S t a t i under s t the i cD se t a i l s table. o fIn order M to e get s the h desired 500 element mesh the B e h a needs v i o to be r changed from S o to f Ht a for r dboth E d g e M e sin the h tree outline then click E d g e

S. In i order z i to n carry g ' this s out first E x p a n d

S andi then z ichange n g B e h a tov Hi ao under rr d the D e t a i l s

o f table, E d

as shown below.


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Then set the B e h a tov Hi ao for rr dE d g e

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S. Next, i z generate i n g the 2 mesh using either method from the "Default Mesh" section

above. You should then obtain the following 500 element mesh.

Radial Sizing

Create Named Selections Here, the edges of the geometry will be given names so one can assign boundary conditions in Fluent in later steps. The left side of the pipe will be called "Inlet" and the right side will be called "Outlet". The top side of the rectangle will be called "PipeWall" and the bottom side of the rectangle will be called "CenterLine" as shown in the image below.

In order to create a named selections first ( C l i c k )

E d g e , S . Then e l e click c on t the i oleftnside Fof the i l rectangle t e r and it

should highlight green. Next, right click the left side of the rectangle and choose C r e a t e

Select the left edge and right click and select C r e a t e


N a m as e shown d Sbelow. e l e c t

N a m .e Enter d Inlet S and e click l e O c tK , as i o shown n below.

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Now, create named selections for the remaining three sides and name them according to the diagram.

Save, Exit & Update First save the project. Next, close the Mesher window. Then, go to the W o r k b e n c h button,

P andr click o jthe e Uc pt d Pa at e g e

.

Go to Step 4: Setup (Physics) See and rate the complete Learning Module Go to all FLUENT Learning Modules




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FLUENT - Laminar Pipe Flow - Setup (Physics) Added by Javier Gutierrez Gallardo , last edited by Benjamin J Mullen on Feb 08, 2012 23:21

Labels: None

Author: Rajesh Bhaskaran, John Singleton, Cornell University Problem Specification 1. Pre-Analysis & Start-Up 2. Geometry 3. Mesh

4. Setup (Physics) 5. Solution 6. Results 7. Verification & Validation Exercises

Useful Inf ormation Click here for the FLUENT 6.3.26 version.

Step 4: Setup (Physics) Your current W o r k b e n c h

P should r olook j ecomparable c t P toathe g following e image. Regardless of whether you downloaded

the mesh and geometry files or if you created them yourself, you should have checkmarks to the right of G e o m and e tMr ey .s h

Next, the mesh and geometry data need to be read into FLUENT. To read in the data ( R i g h t W o r k b e n c h

C l i c k ) in the S e t u

P as shown r o j inethe c image t Pbelow. a g e

https://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Laminar+Pipe+Flow+-+Setup+%28Physics%29

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After you click U p d , a question t e mark should appear to the right of the S e t cell. u p This indicates that the S e t process u p has not yet been completed.

Launch Fluent Double click on S e t inuthep W o r k b e n c h

P which r owillj bring e cupt the P F a L g U eE N T

L. When a u the n Fc Lh U e rE N

L a u n appears c h e change r the options to "Double Precision", and then click O K as shown below.The Double Precision option is used to select the double-precision solver. In the double-precision solver, each floating point number is represented using 64 bits in contrast to the single-precision solver which uses 32 bits. The extra bits increase not only the precision, but also the range of magnitudes that can be represented. The downside of using double precision is that it requires more memory.

Click Here for Higher Resolution Twiddle your thumbs a bit while the FLUENT interface starts up. This is where we'll specify the governing equations and boundary conditions for our boundary-value problem. On the left-hand side of the FLUENT interface, we see various items listed under P r o b l e m . We will S work e t from u ptop to bottom of the P r o b l e mitemsSto e setup t uthepphysics of our boundary-value problem. On the right hand side, we have the G r a p pane h i and, c sbelow that, the C o m m pane. a n d

Check and Display Mesh First, the mesh will be checked to verify that it has been properly imported from W o r k b. In e order n ctohobtain the statistics about the mesh ( C l i c k )

M e s ,has shown > in I the n fimage o below. > S i z e


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Then, you should obtain the following output in the C o m m pane. a n d

The mesh that was created earlier has 500 elements(5 Radial x 100 Axial). Note that in FLUENT elements are called cells. The output states that there are 500 cells, which is a good sign. Next, FLUENT will be asked to check the mesh for errors. In order to carry out the mesh checking procedure ( C l i c k )

M eassshown h in > the C image h e below. c k

You should see no errors in the C o m m Pane. a n Now, d that the mesh has been verified, the mesh display options will be discussed. In order to bring up the display options ( C l i c k )

The previous step should cause the M e s h

G e n e r a las shown > M in the e image s h below. > D i s p l a y

Dwindow i s pto lopen, a yas shown below. Note that the N a m e d

S ecreated l e c

in the meshing steps now appear.


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Click Here for Higher Resolution You should have all the surfaces shown in the above snapshot. Clicking on a surface name in the M e s h

Dmenu i s will p toggle l a y

between select and unselect. Clicking D i s pwilll show a y all the currently selected surface entities in the graphics pane. Unselect all surfaces and then select each one in turn to see which part of the domain or boundary the particular surface entity corresponds to (you will need to zoom in/out and translate the model as you do this). For instance, if you select w a, ol lu t, and l e c t e n t eand r then l i n click D i s pyou l should a y then obtain the following output in the graphics window.

Now, make sure all 5 items under S u r f a arecselected. e s The

button next to S u r f a selects c e allsof the boundaries while the

button deselects all of the boundaries at once. Once, all the 5 boundaries have been selected click D i s p, then l aclose y the M e s h

Dwindow. i s pThe l along, y skinny rectangle displayed in the graphics window corresponds to our solution domain. Some of

the operations available in the graphics window to interrogate the geometry and mesh are: Translation: The model can be translated in any direction by holding down the L e f t

M o u and s ethenB moving u t the t o mouse n in

the desired direction. Zoom In: Hold down the M i d d l e H a n d

L e f t

toHtheaL no dw eC ro r Rn i

Cover o the r narea e you r want to zoom in on.

Zoom Out: Hold down the M i d d l e U p p e r

M o and u sdrag e a box B from u t the t oU np p e r

L e f t . H a n d

M o and u sdrag e a box B u anywhere t t o from n the L o w e r

R i g h t to the H a n d

C o r n e r

Use these operations to zoom in and interrogate the mesh.

Define Solver Properties In this section the various solver properties will be specified in order to obtain the proper solution for the laminar pipe flow. First, the axisymmetric nature of the geometry must be specified. Under G e n e r a l

>

S o lselect A v e r x i> s y 2 m D asmshown S e pt ar

in the image below.


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Click Here for Higher Resolution Next, the V i s c o u sparameters M o d willebel specified. In order to open the Viscous Model Options M o d e l s

>

V i s

L a m i n a r . By>default, E d theiViscous t . . Model . options are set to laminar, so no changes are needed. Click C a n to c exit e the l menu. Now, the Energy Model parameters will be specified. In order to open the Energy Model Options M o d e l s

>

E n e .r

For incompressible flow, the energy equation is decoupled from the continuity and momentum equations. We need to solve the energy equation only if we are interested in determining the temperature distribution. We will not deal with temperature in this example. So leave the E n e r g y

Esetqto u off and a t click i o Cn a n to c exit e the l menu.

Define Material Properties Now, the properties of the fluid that is being modeled will be specified. The properties of the fluid were specified in the Specification section. In order to create a new fluid ( C l i c k )

M a t e r i a l s

Problem

as> shown F lin u theiimage d below. > C r

In the C r e a t e / E d menu i t set M the a Dt e rn istoa1kg/m^3 i l t sy (constant) and set the V i s c o to 2e-3 s i kg/(ms) t y (constant) as shown in the image below.


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Click Here for Higher Resolution Click C h a n g e ./Close C r the e window. a t e

Define Boundary Conditions At this point the boundary conditions for the four N a m e d

condition for the i n lwill e bet S ewilll be e specified. c t i oThe n boundary s

specified first. Inlet Boundary Condition

In order to start the process ( C l i c k )

B o u n d a r y

C oasnshown d i int the i ofollowing n s image. > i n l e t

>

Click Here for Higher Resolution Note that the B o u n d a r y

C oshould n d have i t been i o automatically n T y pset e to v e l o c i . tNow, y -thei velocity n l eattthe i n lwill e

be specified. In the V e l o c i menu t y setI the n Vl ee tl o c i t y

S p e c to i C f i o c ma pt io o ,n and neset nM the A t es t x hi oa dl -

V e l o c i tto y 1 m/s,( as mshown / s below. )

Click Here for Higher Resolution Then, click O K to close the V e l o c i menu. t y I n l e t Outlet Boundary Condition


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First, select o u t inl the e Bt o u n d a r y

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menu, C o as n shown d i t below. i o n s

Click Here for Higher Resolution As can be seen in the image above the T y pshould e have been automatically set to p r e s s u r. Ifethe- To yu pist not el esett to p r e s s u r, then e - set o ituto p t l r ee t s s u r. Now, e - no o further u t lchanges e t are needed for the o u t boundary l e t condition. Centerline Boundary Condition

Select c e n t ein rthel Bi no eu n d a r y


Click Here for Higher Resolution As can be seen in the image above the T y phase been automatically set to w a which l l is not correct. Change the T y pto ae x , iass shown below.


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Click Here for Higher Resolution When the dialog boxes appear click Y e toschange the boundary type. Then click O K to accept "centerline" as the zone name. Pipe Wall Boundary Condition

w B a lo l u n d a r y First, select p i p e _ in the


Click Here for Higher Resolution As can be seen in the image above the T y pshould e have been automatically set to w a. Ifl the l T y pis not e set to w a, then l l set it to w a. Now, l l no further changes are needed for the p i p e _ boundary w a l condition. l

Save

In order to save your work ( C l i c k ) F i l e

as > shown S ain the v eimagePbelow. r o j e c t


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Go to Step 5: Solution See and rate the complete Learning Module Go to all FLUENT Learning Modules




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FLUENT - Laminar Pipe Flow - Solution Added by Javier Gutierrez Gallardo , last edited by Benjamin J Mullen on Feb 08, 2012 23:23

Labels: None

Author: Rajesh Bhaskaran, John Singleton, Cornell University Problem Specification 1. Pre-Analysis & Start-Up 2. Geometry 3. Mesh 4. Setup (Physics)

5. Solution 6. Results 7. Verification & Validation Exercises


Step 5: Solution Second Order Scheme A second-order discretization scheme will be used to approximate the solution. In order to implement the second order scheme click on S o l u t i o n then Mclick e on t hM oo dms e nand t select u mS e c o n d

O r as d shown e r inUthepimage w i below. n d

Click Here for Higher Resolution

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Set Initial Guess Here, the flow field will be initialized to the values at the inlet. In order to carry out the initialization click on

S o l u t i o n

I n

then click on C o m p u t and e select f r i on mlaseshown t below.

Click Here for Higher Resolution Then, click the I n i t ibutton, a l i z e . This completes the initialization.

Set Convergence Criteria FLUENT reports a residual for each governing equation being solved. The residual is a measure of how well the current solution satisfies the discrete form of each governing equation. We'll iterate the solution until the residual for each equation falls below 1e-6. In order to specify the residual criteria ( C l i c k )

M o n i t o r s , as>shown R inethe s image i d u below. a l s

>

E d i t

Click Here for Higher Resolution Next, change the residual under C o n v e r g e n cforec oCn r t i i, x t ne-urv ii eto ly ,and no y c -i tv y e l, all o toc 1e-6, i t as y can be seen below.

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Click Here for Higher Resolution Lastly, click O K to close the R e s i d u a l menu. M o n i t o r s

Execute Calculation Prior, to running the calculation the maximum number of iterations must be set. To specify the maximum number of iterations click on R u n

C a l then c usetl the a N t i u o mn b e r

o f to 100, I t ase shown r a in t the i oimage n s below.

Click Here for Higher Resolution As a safeguard save the project now. Now, click on C a l c utwo l times a t in e order to run the calculation. The residuals for each iteration are printed out as well as plotted in the graphics window as they are calculated. After running the calculation, you should obtain the following residual plot.

Click Here for Higher Resolution The residuals fall below the specified convergence criterion of 1e-6 in about 48 iterations, as shown below. Actual number of convergence steps may vary slightly.

Click Here for Higher Resolution At this point, save the project once again. Go to Step 6: Results See and rate the complete Learning Module Go to all FLUENT Learning Modules


Adaptavist Theme Builder (4.2.4-M1) Powered by Atlassian Confluence 3.5.16, the Enterprise Wiki https://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Laminar+Pipe+Flow+-+Solution

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FLUENT - Laminar Pipe Flow - Results - Simulation - Confluence

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FLUENT - Laminar Pipe Flow - Results Added by Javier Gutierrez Gallardo , last edited by Benjamin J Mullen on Feb 08, 2012 23:28

Labels: None

Author: Rajesh Bhaskaran, John Singleton, Cornell University Problem Specification 1. Pre-Analysis & Start-Up 2. Geometry 3. Mesh 4. Setup (Physics) 5. Solution

6. Results 7. Verification & Validation Exercises


Step 6: Results Velocity Vectors One can plot vectors in the entire domain, or on selected surfaces. Let us plot the velocity vectors for the entire domain to see how the flow develops downstream of the inlet. First, click on G r a p h i c s

& . Next, A ndouble i m click a toni Vo en cs twhich o r isslocated

under G r a p . Then, h i cclick s on D i s p. Zoom l a into y the region near the inlet. (Click here to review the zoom functionality discussion in step 4.) The length and color of the arrows represent the velocity magnitude. The vector display is more intelligible if one makes the arrows shorter as follows: Change S c atol0.4 e in the V e c tmenu o r and s click D i s p. l a y The laminar pipe flow was modeled asymmetrically; however, the plot can be reflected about the axial axis to get an expanded sectional view. In order to carry this out ( C l i c k )

D i s p as shown l a y below. >

V i e w s . . .

Higher Resolution Image Under M i r r o r , only P the l aa nx ei s case. Select a x i s

( o r

( o r

surface c e nis tlisted e rsince l i that n is e the ) only symmetry boundary in the present

and c e click A n t e p rp, as ll shown iy n ebelow. )

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Then click C l o tosexit e the V i e menu. w s Your vector field should have been reflected across the axially axis as, shown below.

Higher Resolution Image The velocity vectors provide a picture of how the flow develops downstream of the inlet. As the boundary layer grows, the flow near the wall is retarded by viscous friction. Note the sloping arrows in the near wall region close to the inlet. This indicates that the slowing of the flow in the near-wall region results in an injection of fluid into the region away from the wall to satisfy mass conservation. Thus, the velocity outside the boundary layer increases. By default, one vector is drawn at the center of each cell. This can be seen by turning on the grid in the vector plot: Select D r a w in G the rV i e dc tmenu o r and s then click D i s pin lthea Gy r i d

Dasi well s p as the l a y

V e c tmenus. o r sVelocity vectors are the default, but you can also plot other vector quantities. See section 27.1.3 of the user manual for more details about the vector plot functionality.

Centerline Velocity Here, we'll plot the variation of the axial velocity along the centerline. In order to start the process ( C l i c k ) P l o t . . .

R e s u l t

as > shown S ebelow. t U p . .

Higher Resolution Image In the S o l u t i o nmenuXmake Y sure P lthat o Pt o s i t i o n is o selected n X, and X is A x set i s to 1 and Y is set to 0. This tells FLUENT to plot the x-coordinate value on the abscissa of the graph. Next, select V e l o cfori the t first y . box . .underneath Y F u n c and t i select A o n x i a l

Vforethel second o c ibox. t y Please note that X


A x i s

F anduY n cA t xi io s n

A x i

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the x and y axes of the g r a, which r l i p h should not be confused with the x and y directions of the pipe. Finally, select c e n t eunder S u r f a since c we e sare plotting the axial velocity along the centerline. This finishes setting up the plotting parameters. Your S o l u t i o nshould X look Y exactly P l the o tsame as the following image.

Higher Resolution Image Now, click P l .oThe t plot of the axial velocity as a function of distance along the centerline now appears.

Higher Resolution Image In the graph that comes up, we can see that the velocity reaches a constant value beyond a certai n distance from the inlet. This is the fully-developed flow region. At this point the graph will be modified such that the fully developed regions results are truncated. That is, the range of the axes will be reconfigured. Open the S o l u t i o nmenu, X then Y click P on A l o tx e , as s shown . . . below.

Higher Resolution Image Then, deselect A u t o

,Rwhich a nis located g e under O p t i. The o nboxes s under R a n should g e now be accessible. Next, select X ,

which is located under A x . iEnter andu3 for under s 1 for M i n i m mM a x i m u R m a n. At g this e point the grid lines will be turned on in order to help estimate where the flow becomes fully developed. Check the boxes next to M a j o r O p t i. At o this n point s your A x e s

-

and R Mu il ne o s r under R u

S o l umenu t i should o n look X exactly Y P thelsame o t as the image below.

Higher Resolution Image Lastly, click A p p. Now, l y that the X axis has been formatted, we will move on to formatting the Y axis. Select Y under A x and i s https://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Laminar+Pipe+Flow+-+Results

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once again deselect A u t o

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R under a n O gp et i. Then, o n enter s andu2.0 m for M a x i m under u R m a n. Also g e 1.8 for M i n i m

select M a j o r and R Mu il ne o s r toR turnuonl the e grid s lines in the direction. At this point your A x e s

-

S o l umenu t i should o n look X exactly Y Pthelsame o t as the image below.

Higher Resolution Image We have now finished specifying the range for each axis, so click A p pand l then y C l o. At s this e point, the graph can be replotted. Go to the S o l u t i o nmenu Xand Y click P Pl lo to ot plot t the graph again with the new axes extents.

Higher Resolution Image From the image above, one can see that the fully-developed region starts at around x =3m and the centerline velocity in this region is

1 . 9 3.

m / s

Saving the Plot In this section, we will save the data from the plot and a picture of the plot. The data from the plot will be saved first. In order to save the plot data open the S o l u t i o nmenuXand Y then P select l o W t r i t e , which t o is located F i l under e O p t i. The o nP sl button o t should have changed to W r i .tClick e . on . W . r i ,t and e then . . enter . File Name. Next, click O K . Check that this vel.xy as the X Y file has been created in your FLUENT working directory. Lastly, close the S o l u t i o nmenu. X Y At this point, we'll save a picture of the plot. First click on F i then l e click S a v e

P l o t

P, asi shown c t ubelow. r e

Under F o r ,m choose a t one of the following three options: E P - ifS you have a postscript viewer, this is the best choice. E P allows S you to save the file in vector mode, which will offer the best viewable image quality. After selecting E P , choose S V e c from t o under r F i l e . T y p e T I F - this F will offer a high resolution image of your graph. However, the image file generated will be rather large, so this is not https://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Laminar+Pipe+Flow+-+Results

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recommended if you do not have a lot of room on your storage device. J P - G this is small in size and viewable from all browsers. However, the quality of the image is not particularly good. After selecting your desired image format and associated options, click on S a v e . . . Enter vel.eps, vel.tif, or vel.jpg depending on your format choice and click O K . Verify that the image file has been created in your working directory. You can now copy this file onto a disk or print it out for your records.

Coefficient of Skin Friction FLUENT provides a large amount of useful information in the online help that comes with the software. Let's probe the online help for information on calculating the coefficient of skin friction. In order to access the online help first ( c l i c k )

H e l p

>

I n d as e shown x in the following image.

Click on S in the links on top and scroll down to s k i n

f r i c t i .o Click n on the c ofirst e link f f(normally, i c i eyounwould t have to go

through each of the links until you find what you are looking for). There you can see the following excerpt on the skin friction coefficient as well as the equation for calculating it.

Click on the link for R e f e r e n cpanel, e which V a tells l u use how s to set the reference values used in calculating the skin coefficient. In order to set the reference values, click on R e f e r e n c, as e shown V a below. l u e s

Then, set C o m p u t to e i nF ,l to r etell ot FLUENT m to calculate the reference values from the values at inlet. Check that density is 1 k g 3/ and m velocity is 1

you could have just typed i n the appropri ate values). Your R e f e r e n cshould e V a m. (Alternately, / s

look the same as the following screen snapshot. https://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Laminar+Pipe+Flow+-+Results

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Higher Resolution Image Now, reopen the S o l u t i o nmenu. X Uncheck Y P the l oW t r i t e window. The O p t i and o n P s l o t the Y

A x i s

check t o boxFunder i l O e p t i, since o n we s want to plot to the

D ican r be e left c tasiis osince n we are still plotting against the x distance along the pipe. Under

,Fpick u W n c a tl il o Fn , land u then x eS sk . i . n.

F r i c t i o in the n boxCunder o ethat. f fUnder i c Si eu nr tf , aonly c e

select p i p e _ . Atwthisapoint, l l your S o l u t i o nmenuXshould Y look P l exactly o t like the following image.

Higher Resolution Image Now, the ranges of each axis will be speci fied. Click on A x e within s . .the. S o l u t i o nmenu Xand Y re-select A P l o t u t o - R for the Y axis. Click A p p. Set l y the range of the X axis from 1to 8 by selecting X under A x , ientering s andu8 m 1 under M i n i ,m under M a x i m in the u box m (remember to deselect R a n g e

A u first t oif it- isRchecked). a n g Click e A p p, then l y click C l o. s e

Lastly, click P l in o the t S o l u t i o nmenu. X You Y should P l obtain o t the following plot.

Higher Resolution Image We can see that the fully developed region is reached at around x=3.0m and the skin friction coefficient in this region is around 1.54. In order to save the data from this plot, first reopen the S o l u t i o nmenu. X Then, Y select P l o W tr i t e click W r i .tEnter e . cf.xy . . for X Y

under t o O Fp it li and eo n

Fandi click l e O K .

Velocity Profile In this section we will plot the velocity at the outlet as a function of the distance from the center of the pipe. In order to start the process ( C l i c k )

R e s u l t s

>

P l aso shown t s below. > X Y


P l o t . . .

>

S e t

U p . .

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Higher Resolution Image For this graph, the y axis of the graph will have to be set to the y axis of the pipe (radial direction). To plot the position variable on the y axis of the graph, uncheck P o s i t i o n under and o nO pX t i A o xchoose n i ss P o s i t i o n instead. o n ToYmake Athe x position i s variable the radial distance from the centerline, under P l o t axis of the graph, select V e l o cfori the t first y . box . .underneath X

D ,ichange X to r e c t i0 and o nY to 1. To plot the axial velocity on the x A x i s

,Fand u select A n c t ix oi n a l

Next, select o u t, which l e tis located under S u r f .aThen, c euncheck s the W r i t e

Vforethel second o c ibox. t y

check t o boxFunder i l O e p t i, so o the n graph s

will plot. Your S o l u t i o n , should X look Y exactly P l oliket the image below.

Higher Resolution Image Next, click on A x ein the s S o l u t i o nmenu. X Then, Y change P l oboth t the x and y axes to A u t o - R . (Don't a nforget g eto click apply before selecting a different axis). Click C l o insthe A e x e s

-

S o l umenu. t i o n

X Y

P l o t

It is of interest to compare the velocity profile with the theoretical parabolic profile. In order to plot the theoretical results, first click

here

to download the necessary file. Save the file to your working directory. Next, go to the S o l u t i o nmenu Xand Y click P Ll oo at d F i l and e . select . . the file that you just downloaded, p r o f i l e . Lastly, o y the t S o l u t i o nmenu. X You Y should P l _ f dclick e vP . l xin then obtain the following figure.

Higher Resolution Image Notice, how results compare relatively well with the theoretical parabolic profile. In order to save the data from this plot, first reopen the S o l u t i o nmenu. X Then, Y select P l o W tr i t e

under t o O Fp it li and eo click n s W r i .tEnter e . profile.xy . . for X Y

F i

and click O K . To see how the velocity profile changes in the developing region, we will add profiles at x=0.6m (x/D=3) and x=0.12m (x/D=6) to the previous plot. In order to create the profiles, we must first create vertical lines using the L i n e / tool. R aFirst, k (e C l i c k )

S

L i n e / as R shown a k ine the following image. https://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Laminar+Pipe+Flow+-+Results

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We'll create a straight line from (x0,y0)=(0.6,0) to (x1,y1)=(0.6,0.1). Select L i n e under T oO op l t i. Enter x o n s= 0 0.6 , y = 0 0 ,x = 10.6 , y = 10.1 . Enter line1 under N e w

To see the line that you just created, ( C l i c k )

S u r f .a Click c C e r N e .a m t ee

D i .sNote p lthat a l yi nappears > e 1M ine the s list h of surfaces. Select all surfaces

except d e f a u l t . Click - i nD t i es rp. This i l oadisplays r y all surfaces but not the mesh cells. Zoom into the region near the inlet to see the line created at x=0.6m. (Click here to review the zoom functionality discussion in step 4.) The white vertical line appearing to the right is l i n, as in the image below. e shown 1

Similarly, create a vertical line called l i natex=1.2; 2 (x0,y0)=(1.2,0) to (x1,y1)=(1.2,0.1). Display it in the graphics window to check that it has been created correctly. Now, we can plot the velocity profiles at x=0.6m (x/D=3) and x=0.12m (x/D=6) along with the outlet profile. First, open the S o l u t i o nmenu. X Under Y S P u l or tf ,a in addition c e s to o u t, select l e tl i n and e 1 l i n. Make e 2 sure N o d e

Vis selected a l u eunder s O p t i. Now, o n your s S o l u t i o nmenuXshould Y look P l exactly o t like the following image.

Higher Resolution Image Lastly, click P l and o t you should obtain the following output. Your symbols might be different from the ones below. You can change the symbols and line styles under the C u r v button. e s .Click . . on H e in l the p C u r menu v e sif you have problems figuring out how to https://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Laminar+Pipe+Flow+-+Results

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change these settings.

Higher Resolution Image The profile three diameters downstream is fairly close to the fully-developed profile at the outlet. If you redo this plot using the fine grid results in the next step, you'll see that this is not actually the case. The coarse grid used here doesn't capture the boundary layer development properly and under predicts the development length. In FLUENT, you can choose to display the computed cell-center values or values that have been interpolated to the nodes. By default, the Node Values option is turned on, and the interpolated values are displayed. Node-averaged data curves may be somewhat smoother than curves for cell values. Go to Step 7: Verification & validation See and rate the complete Learning Module Go to all FLUENT Learning Modules




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FLUENT - Laminar Pipe Flow - Verification & Validation - Simulation - Confluence

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FLUENT - Laminar Pipe Flow - Verification & Validation Added by Steve Weidner , last edited by Benjamin J Mullen on Feb 08, 2012 23:30

Labels: None

Author: Rajesh Bhaskaran, John Singleton, Cornell University Problem Specification 1. Pre-Analysis & Start-Up 2. Geometry 3. Mesh 4. Setup (Physics) 5. Solution 6. Results

7. Verification & Validation Exercises

Step 7: Verification & Validation It is v e r y

i mthat p you o rtake t the a n time t to check the validity of your solution. This section leads you through some of the steps

you can take to validate your solution.

Refine Mesh Let's repeat the solution on a finer mesh. For the finer mesh, we will use increase the radial divisions from 5 to 10. In the W o r k b e n c h

P right r click o j on e Mc et sthen Ph click a g De u p l iascshown a t below. e

Higher Resolution Image Rename the duplicate project to L a m i n a r P r o j e c. t

P i p e . You F should l o w have the ( m following e s two h projects 2 ) i n your W o r k b

P a g e


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Next, double click on the M e scellhof the L a m i n a r Under O u t ,l expand i n eM e sand h click on E d g e

P i p e project. F l Aonew w ANSYS ( m Mesher e s hwindow 2 )will open.

,Sas ishown z i below. n g

Under Details of "Edge Sizing", enter 10 for N u m b e r

o f, as shown D i vbelow. i s i o n s

Higher Resolution Image Then, click U p d to a generate t e the new mesh.

The mesh should now have 1000 elements (10 x 100). A quick glance of the mesh statistics reveals that there is indeed 1000 elements.

Higher Resolution Image

Compute the Solution Close the ANSYS Mesher to go back to the W o r k b e n c h F l u i d

.PUnder r o L j ae m c ti n Pa ar g Pe i p e , right F click l o on w

F l o wand (click F on L U U pE dN, a asTtshown )e below.


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Higher Resolution Image Now, wait a few minutes for FLUENT to obtain the solution for the refined mesh. After FLUENT obtains the solution, save your project.

Velocity Profile In order to launch FLUENT double click on the S o l u oft the i o"Laminar n Pipe Flow (mesh 2)" project in the W o r k b e n c h P a .gAfter, e FLUENT launches ( C l i c k )

P l o t s

> as shown X Y in the P limage o t below. >

S e t U p . . .

For this graph, the y axis of the graph will have to be set to the y axis of the pipe (radial direction). To plot the position variable on the y axis of the graph, uncheck P o s i t i o n under o nO pX t i A and o xchoose n i ss P o s i t i o n instead. o n ToYmake Athe x position i s variable the radial distance from the centerline, under P l o t axis of the graph, select V e l o cfori the t first y . box . .underneath X

D ,ichange X to r e c t i0 and o nY to 1. To plot the axial velocity on the x A x i s

,Fand u select A n c t ix oi n a l

Next, select o u t, which l e tis located under S u r f .aThen, c euncheck s the W r i t e

Vforethel second o c ibox. t y

check t o boxFunder i l O e p t i, so o the n graph s

will plot. Now, your S o l u t i o nmenu Xshould Y look P l exactly o t like the following image.

Higher Resolution Image Since we would like to see how the results compare to the courser mesh and the theoretical solution, we will load the p r o f ifile, l e which was created in the previous step. In order to do so, click L o a d

inF the i S l eo . l . u. t i o nmenu, X then Y select P l the o t

p r o f ifile. l Click e . xO y K , then click P l in o the t S o l u t i o nmenu. X You Y should P l then o tobtain the following plot.


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Higher Resolution Image In the plot above the green dots correspond to the theoretical solution, the red dots correspond to the rough mesh ( 5 x 100 ), and the white dots correspond to the refined mesh ( 10 x 100 ). Note how the refined mesh results resemble the theory signicantly more than the rough mesh.

Further Verification The plot below shows the results of a further refined mesh ( 20 radial x 100 axial ) and the theoretical results.

Higher Resolution Image Notice that for the further refined mesh, the results are almost indistinguishable from theory. Go to Problem 1 See and rate the complete Learning Module Go to all FLUENT Learning Modules




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FLUENT - Laminar Pipe Flow - Exercises - Simulation - Confluence

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FLUENT - Laminar Pipe Flow - Exercises Added by Steve Weidner , last edited by Benjamin J Mullen on Apr 27, 2011 18:01

Labels: None

Problem Specification 1. Pre-Analysis & Start-Up 2. Geometry 3. Mesh 4. Setup (Physics) 5. Solution 6. Results 7. Verification & Validation

Exercises

Exercises Consider developing flow in a pipe of length L = 8 m, diameter D = 0.2 m, ρ = 1 kg/m3 , µ =2 × 10^−3 kg/m s, and entrance velocity u_in = 1 m/s (the conditions specified in the Problem Specification section). Use FLUENT with the "second-order upwind" scheme for momentum to solve for the flowfield on meshes of 100 × 5, 100 × 10 and 100 × 20 (axial divisions × radial divisions). 1. Plot the axial velocity profiles at the exit obtained from the three meshes. Also, plot the corresponding velocity profile obtained from fully-developed pipe analysis. Indicate the equation you used to generate this profile. In all, you should have four curves in a single plot. Use a legend to identify the various curves. Axial velocity u should be on the abscissa and r on the ordinate. 2. Calculate the shear stress Tau_xy at the wall in the fully-developed region for the three meshes. Calculate the corresponding value from fully-developed pipe analysis. For each mesh, calculate the % error relative to the analytical value. Include your results as a table:

3. At the exit of the pipe where the flow is fully-developed, we can define the error in the centerline velocity as

where u_c is the centerline value from FLUENT and u_exact is the corresponding exact (analytical) value. We expect the error to take the form

where the coefficient K and power p depend upon the order of accuracy of the discretization. Using MATLAB, perform a linear least squares fit of

https://confluence.cornell.edu/display/SIMULATION/FLUENT+-+Laminar+Pipe+Flow+-+Exercises

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Laminar Pipe Flow Cornell

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