OPTIMIZATION OF RADIAL FAN IMPELLER USING FINITE ELEMENT ANALYSIS A PROJECT REPORT
Submitted by
KISHORE KANNA.B MOHAMMED MOHAIDEEN.M PANDIARAJ.T SATHISH KUMAR.K
40401114020 40401114033 40401114039 40401114049
in partial fulfillment for the award of the degree of
BACHELOR OF ENGINEERING
in MECHANICAL ENGINEERING
B.S.ABDUR RAHMAN CRESCENT ENGINEERING COLLEGE, CHENNAI-48
ANNA ANN A UNIVERSITY: UNIVERSITY: CHENNAI 600 025
MAY 2005
BONAFIDE CERTIFICATE
This This is to cert certif ify y that that the the proj projec ectt work work enti entitl tlee “ OPTIMIZATI OPTIMIZATION ON OF
RADIAL FAN IMPELLER USING FINITE ELEMENT ANALYSIS” is a Bonafide record of the work done by
KISHORE KANNA.B
-
40401114020
MOHAMMED MOHAIDEEN.M
-
40401114033
PANDIARAJ.T
-
40401114039
SATHISH KUMAR.K
-
40401114049
Stud Studen ents ts of B.E., .E., (Mec (Mecha hani nica call Engi Engine neer erin ing) g) of B.S B.S ABDU ABDUR R RAHMAN CRESCENT ENGINEERING COLLEGE, Chennai at Ranipet. During the period from 31-01-05 to 28-02-05.
We wish them all the success in their future endeavour.
For BHARAT HEAVY ELECTRICALS LIMITED
Mr. R.BABU M.Tech (IIT-Madras)
Mr.S.PARAMANANTHAM
Deputy Manager (Fans)
H.R.D.Officer
BHEL-BAP
BHEL-BAP
Ranipet
Ranipet
This This is to cert certif ify y that that the the proj projec ectt work work enti entitl tlee “ OPTIMIZATI OPTIMIZATION ON OF
RADIAL FAN IMPELLER USING FINITE ELEMENT ANALYSIS” is a Bonafide record of the work done by
KISHORE KANNA.B
-
40401114020
MOHAMMED MOHAIDEEN.M
-
40401114033
PANDIARAJ.T
-
40401114039
SATHISH KUMAR.K
-
40401114049
Stud Studen ents ts of B.E., .E., (Mec (Mecha hani nica call Engi Engine neer erin ing) g) of B.S B.S ABDU ABDUR R RAHMAN CRESCENT ENGINEERING COLLEGE, Chennai at Ranipet. During the period from 31-01-05 to 28-02-05.
We wish them all the success in their future endeavour.
For BHARAT HEAVY ELECTRICALS LIMITED
Mr. R.BABU M.Tech (IIT-Madras)
Mr.S.PARAMANANTHAM
Deputy Manager (Fans)
H.R.D.Officer
BHEL-BAP
BHEL-BAP
Ranipet
Ranipet
ANNA UNIVERSITY: CHENNAI 600 025
BONAFIDE CERTIFICATE
This is to certify that the project report ‘ OPTIMIZATION OF RADIAL
FAN FA N IMPE IMPELL LLER ER USIN USING G FINI FINITE TE ELEM ELEMEN ENT T AN ANAL ALYS YSIS IS’’ is the bonafide work of
KISHORE KANNA.B MOHAMMED MOHAIDEEN.M PANDIARAJ.T SATHISH KUMAR.K
40401114020 40401114033 40401114039 40401114049
Who carried out the project work under my supervision.
Dr.R.GANESAN HEAD OF THE DEPARTMENT
Mr.P.GANESH INTERNAL GUIDE
DEPARTMENT OF MECHANICAL ENGINEERING B.S.ABDUR RAHMAN CRESCENT ENGINEERING COLLEGE CHENNAI-48
VIVA VOCE EXAMINATION
The viva voce examination of this project work submitted by
B.KISHORE KANNA,
REGISTER NO: 40401114020
T.PANDIARAJ,
REGISTER NO: 40401114039
K.SATHISH KUMAR,
REGISTER NO: 40401114049
M.MOHAMMED MOHAIDEEN, REGISTER NO: 40401114033
is held on
EXTERNAL EXAMINER
INTERNAL EXAMINAR
ACKNOWLEDGEMENT
AKNOWLEDGEMENT It is our great pleasure in presenting the project work undergone at Bharat heavy electrical limited (BHEL), Ranipet. At this moment we wish to place on record our sincere gratitude to prof. S.Peer Mohamed, Correspondent and Dr.K.P.Mohamed, Principal, for their encouragement. Our sincere gratitude to our Head of the Department Dr.R.Ganesan and Project coordinator Mr.J.Bhaskaran for providing us with necessary infrastructure. Our sincere gratitude to Mr.P.Ganesh, Lecturer who has been a resource of encouragement and guidance for our project work. We are indebted towards him for his valuable suggestions and help without which our project could not have been completed. We express our sincere gratitude and thanks to Mr.S.Paramananthan, HRDC Officer, BHEL- Ranipet. Our sincere gratitude and thanks to our External guide Mr.R.Babu, Deputy Manager, BHEL-Ranipet. Our sincere thanks to all the staff members of our department for their encouragement and guidance. Last but not least we thank all of our friends who stood by us and provided the moral support during the preparation of our project work.
ABSTRACT
ABSTRACT
Increasing cost of consumable materials has put an enormous pressure on the pricing as well as the profitability of an organization. Therefore without any compromise on quality, the variable cost has to be reduced. This demands novel thinking and creativity for constant improvement in design, resulting in good profits. In this project work, an attempt has been made to optimize the design of aerofoil bladed radial fan impeller using finite element analysis ( FEA). The optimization is done using FEA in “ ANSYS – MECHANICAL
UTILITY” In the FEA section, modeling as well as analysis was done using ANSYS MECHANICAL UTILITY. In this section, the thickness of the every component of the impeller was reduced and Stiffeners were provided to curtail the large deflections in the optimized model. Stresses and deflections were analyzed for the modified and pre modified model. The results of the optimization were successful as 18.5% savings in net
weight after FEA optimization. So, the material cost is reduced and also the space occupied. In FEA the stress and deflection analysis were performed whose results were well within the limits.
CONTENTS
CHAPTER
PAGE NO
ACKNOLEDGEMENT
i
ABSTRACT
ii
CONTENTS
iii
LIST OF DIAGRAMS
vi
LIST OF TABLES
vii
LIST OF NOMENCLATURE
viii
CHAPTER 1
INTRODUCTION
1.1
Organization Profile
1.2
BHEL – Boiler auxiliary plant ranipet
1.3
About the Project.
1 1 2
1.4 About the Fan
3
1.5
Classification of fans
3
1.6
Advantages of an Aerofoil Bladed Fan
6
1.7
Constructional features of a radial fan
7
1.8
Methods to drive the Fan
8
1.9
Fan specifications
9
CHAPTER 2
LITERATURE REVIEW
2.1
Introduction
10
2.2
Historical Background
2.3
What is FEA?
11
2.4
Need for Finite Element Analysis
11
2.5
The Finite Element Method
12
2.6
Concepts of FEA
13
2.7
General procedure for FEA
14
2.8
Applications of FEA
16
2.9
Setting element attributes
16
2.10
Boundary conditions
17
2.11
Material properties
18
2.12
Element type
18
10
2.13
Fan laws and Efficiency
22
2.14
Stress Analysis
28
CHAPTER 3
INTRODUCTION ANSYS
3.1
Introduction to ANSYS
3.2
ANSYS offers
31
3.3
Examples of ANSYS analysis
31
3.4
Choosing the software
32
3.5
Feature selection
33
3.6
Results required for analysis
33
3.7
Solution speed
33
3.8
Hardware availability
33
3.9
Analysis procedure
34
3.10
Procedure for static analysis
35
3.11
Modal analysis
36
3.12
Procedure for modal analysis
37
3.13
Design optimization
38
3.14
Typical examples of optimized designs
38
CHAPTER 4
31
METHODOLOGY 4.1.
Solid model generation using preprocessor
39
4.2.
Meshing contours
39
4.3.
Meshing of areas
39
4.4.
Defining material
40
4.5.
Choosing appropriate element for analysis
40
4.6.
Attributing equivalent and actual boundary
40
4.7.
Solving the problem using solver
40
4.8.
Viewing results
41
4.9.
Studying the parameters stress and deflection
41
4.10.
CHAPTER 5
Modifying the geometry model by reducing the thickness
41
MODELING
5.1
Segment generation
42
5.2
Real constants for the model
43
5.3
Mapped mesh
45
5.4
Generation of fan impeller
46
5.5
Boundary condition
47
5.6
Solution
48
CHAPTER 6
RESULT AND DISCUSSION
6.1
Static analysis
49
6.2
Optimization
49
6.3
Results for fan impeller original thickness
50
6.4
Results for optimized fan impeller
58
CHAPTER 7
CONCLUSION
7.1.
Real constants for the model
66
7.2
Weight reduction
67
REFERENCES
LIST OF FIGURES
PAGE NO
FIG.1- LINE PLOT OF FAN IMPELLER SEGMENT
42
FIG.2- AREA PLOT OF FAN IMPELLER SEGMENT
43
FIG.3- REAL CONSTANT NUMBERING FOR THE SEGMENT
44
FIG.4- MAPPED MESH OF THE SEGMENT
45
FIG.5-FAN IMPELLER MODEL WITH REAL CONSTANT NUMBERING
46
FIG.6-MAPPED MESH OF THE IMPELLER MODEL
46
FIG.7- CONSTRAINTS AT THE CENTRE
47
FIG.8- MESH OF IMPELLER WITH CONSTRAINTS
48
FIG.9- ORIGINAL FAN IMPELLER DEFLECTION PLOT
50
FIG.10- ORIGINAL FAN IMPELLER STRESS PLOT
51
FIG.11- ORIGINAL BACKPLATE (BOTTOM) DEFLECTION PLOT
52
FIG.12- ORIGINAL BACK PLATE (BOTTOM) STRESS PLOT
52
FIG.13- ORIGINAL BACK PLATE (TOP) DEFLECTION PLOT
53
FIG.14- ORIGINAL BACK PLATE (TOP) STRESS PLOT
53
FIG.15- ORIGINAL BLADE DEFLECTION PLOT
54
FIG.16- ORIGINAL BLADE STRESS PLOT
54
FIG.17- ORIGINAL COVER PLATE DEFLECTION PLOT
55
FIG.18- ORIGINAL COVER PLATE STRESS PLOT
55
FIG.19- ORIGINAL RING DEFLECTION PLOT
56
FIG.20- ORIGINAL RING STRESS PLOT
56
FIG.21- ORIGINAL FLANGE DEFLECTION PLOT
57
FIG.22- ORIGINAL FLANGE STRESS PLOT
57
FIG.23- OPTIMIZED FAN IMPELLER DEFLECTION PLOT
58
FIG.24- OPTIMIZED FAN IMPELLER STRESS PLOT
59
FIG.25- OPTIMIZED BACKPLATE (B (BOTTOM) DE DEFLECTION PLOT
60
FIG.26- OPTIMIZED BACK PLATE (BOTTOM) STRESS PLOT
60
FIG.27- OPTIMIZED BACK PLATE (TOP) DEFLECTION PLOT
61
FIG.28- OPTIMIZED BACK PLATE (TOP) STRESS PLOT
61
FIG.29- OPTIMIZED BLADE DEFLECTION PLOT
62
FIG.30- OPTIMIZED BLADE STRESS PLOT
62
FIG.31- OPTIMIZED COVER PLATE DEFLECTION PLOT
63
FIG.32- OPTIMIZED COVER PLATE STRESS PLOT
63
FIG.33- OPTIMIZED RING DEFLECTION PLOT
64
FIG.34- OPTIMIZED RING STRESS PLOT
64
FIG.35- OPTIMIZED FLANGE DEFLECTION PLOT
65
FIG.36- OPTIMIZED FLANGE STRESS PLOT
65
LIST OF TABLES TABLE 2.1- ELEMENT TABLE
19
TABLE .5.2- REAL CONSTANTS FOR THE MODEL
43
TABLE.6.1- OPTIMIZATION TABLE
49
TABLE.7.1- DIMENSIONS FOR THE MODEL
66
NOMENCLATURE N
-
rpm
D
-
Fan diameter (mm)
µ
-
dynamic viscosity
Ns
-
Specific speed
Q
-
Volume flow rate (m3/sec)
gH
-
specific energy (J/kg)
P
-
Pressure rise (pa)
ρ
-
fluid density (kg/m 3)
CHAPTER 1
INTRODUCTION
CHAPTER1 INTRODUCTION
1.1 Organization Profile M/S. BHARAT HEAVY ELECTRICAL LTD., popularly known as BHEL is today, the largest engineering and manufacturing enterprise of its kind among the public sector undertakings in India. The company provides products, systems and services in the field of energy and transportation for domestic and export markets. The company ranks amongst the worlds top 10 organizations engaged in the manufacturing of power plant equipment. About 50 countries, extending from USA in the west to Australia and New Zealand in the far east are BHEL’s customers.
1.2 BHEL - BOILER AUXILIARIES PLANT - RANIPET
BHEL – Trichy launched its phase III expansion for augmentation of manufacturing capacity to 4,000 MW for boilers and auxiliaries at Ranipet Tamilnadu in 1982.
The product profile of BAP, Ranipet is Fans – Radial, Axial, Impulse and Axial reaction Electrostatic precipitators Air preheater (Regenerative type)
These auxiliaries play a vital role in the thermal power plants. There are 43 ancillaries established adjacent to the plant .BHEL gives by
way of technical , raw material and quality control procedure , BAP Ranipet has technical collaboration with M/S K.K.K, West Germany for fans . BAP at Ranipet provides direct employment to about 3,000 employees and indirect employment of over 10,000 employees. BHEL is certified with ISO 9001 and ISO 9002 by BVQI.
1.8 About the Project.
This project has been done to predict and give the results of a Radial fan impeller under physical operating conditions. The Radial fan impeller is analyzed before the performance testing and installation. Stress analysis is performed to find the maximum stress values. These analysis are done by ANSYS. In this project static and optimization of fan impeller thickness have been performed during the analysis using the software. In static analysis the maximum stress, strain values for the required boundary conditions are found. In optimization, the impeller thickness is reduced or optimized without changing or violating the maximum stress values. So that the weight reduces and hence the cost of the product also reduces. HARDWARE REQUIREMENTS
Processor
:
PENTIUM III
CPU speed
:
400Mhz
HDD
:
20GB
Main memory capacity:
159MB
SOFTWARE REQUIREMENTS
ANSYS 5.4
1.9 About the Fan
A fan is a turbo machine used for energy transfer. It can be defined as a rotating machine with a bladed impeller, which maintains a continuous flow of air (or) gases. Fans usually consist of a single rotor with or without a stator element and cause a rise in pressure of the flowing fluid.
PRINCIPLE OF WORKING : The principle involved is that the mechanical energy owing to the rotation of the fan is converted into the fluid energy (in the form of pressure rise). Fans obviously consume power as they rotate with the help of prime mover and energize the flowing fluid.
1.5 CLASSIFICATION OF FANS: 1.5.1 ACCORDING TO PURPOSE: 1. Primary Air Fan :( PA FAN) Primary air fans supply the air needed to dry and transport pulverized coal to the furnace of direct-fired boiler.
2. Forced Draught Fan: (FD FAN) The forced draught fans supply the air-required for the combustion of fuel and normally handle stoichiometric plus excess air required for the satisfactory burning of fuel.
3. Induced Draught Fan: (ID FAN) The induced draught fans draw the products of combustion from the boiler while creating sufficient draught (negative pressure) in the furnace for balanced draught operation.
1.5.2 ACCORDING TO FLOW OF AIR:
1. Radial Fan: A radial fan is a one in which the flow enters along the axis and leaves in the radial direction along the blades. It can be used for PA, FD and ID applications. Based on the configuration of the blade with respect to the direction of rotation of the impeller (AS SHOWN IN THE FIG.) it is called
backward curved, forward curved and radial bladed impeller
2
< 90
2
= 90
2
> 90
FIG. 1.1
2. Axial Fans: An axial fan is a one in which the main flow is along the axis of rotation both at entry and exit. Based on the profile these fans are mainly classified into two types namely,
I Axial Profile Impeller: (AP IMPELLER) In this type, the impeller has a central hub which is spherical in nature and has blades with individual shafts located along the periphery. The hub is a high precision part which is ball turned to get a curved smooth profile. The individual blades of the impeller are driven with the help of hydraulic mechanism.
II Axial Non – Profile Impeller: (AN IMPELLER) In this type, the impeller has a central hub, which is of hemispherical nature and has blades curved at a fixed angle and welded to the hub as in case of its radial counterpart. Both the fans described above have an inlet guide vane (IGV) and an outlet guide vane (OGV) along with a diffuser at the exit.
AEROFOIL BLADED RADIAL FAN - A GLANCE An aerofoil bladed radial fan consists of blades, which are profiled, in an aerofoil shape as shown in the figure below:
FIG .1.2
1.6 Advantages of an Aerofoil Bladed Fan: a. Since the aerofoil is a profile curved body, it ensures a smoother flow than a blunt body and hence no flow separation thereby minimized losses
b. Because of higher efficiency than normal plate bladed impeller it consumes less power and hence it is economical. c. An aerofoil bladed fan has the higher half – load efficiency like an axial fan and the rigidity of that of a radial fan and hence the combined feature of both. But the aerofoil bladed is mostly employed as primary air fan.
1.7 CONSTRUCTIONAL FEATURES OF A RADIAL FAN: The fan as a whole can be divided in to some major sub – assemblies.
1. SPIRAL CASING: The spiral casing consists of two parallel sidewalls, spiral wall, Suction Chamber and inlet cone. It is split horizontally along the shaft axis plane; if necessary the upper portion will also be vertically split off at the center so that impeller installation is easy. The inlet cone and the suction chamber are welded to the sidewalls.
2. IMPELLER: The impeller is a completely welded structure. It consists of a center plate (or) back plate, cover plate and blades. The blades are welded between the back plate and the cover plate. Proper welding sequence is followed to have minimum distortion.
3. SHAFT: The shaft is a hollow tube with 2 endpins shrunk-fit at the 2 ends is welded. Torque is transmitted through the fit and the weld is only
for securing purpose. The tube is controlled at the inside diameter. The shaft ends are machined after welding. A flat split ring is welded on to the shaft tube for taking up the shaft flange. The complete shaft is dynamically balanced.
4. BEARINGS: The impeller is mounted on pillow block bearings. One is a locating bearing while the other is a non – locating (FREE) bearing. The bearings are spherical roller type housed in bearing housing. Or the bearings are of sleeve types that are selected based on the contractual requirement and or on the basis of the selection requirement.
5. DAMPER ASSEMBLY: This consists of a single piece casing, damper flaps, damper bearings and the actuating mechanism. It is welded casing flanged at both the ends. The bearing pedestals are mounted to the sidewalls by screws. There are 3 to 5 flaps fixed by screws on to their shafts, which are supported by pedestals providing dry lubrication. The flat shafts carry clamping levers and feather keys transmit the adjusting torque and a linkage connects the individual clamping levers.
6. SEALS: The sealing for the shaft with the spiral casing consists of a labyrinth section For axial and asbestos strip for radial sealing. The asbestos strip ensures that the movement of the spiral casing during hot conditions relative to the impeller wheel does not attack the fan’s functioning. The unmachined flanges of the spiral casing are sealed with asbestos rope.
1.8 Methods to drive the Fan
Various methods are used to the Fan Prime movers Electric motors (the most commonly used) Engines Turbines (compressed air to steam) Compressed air jets.
1.8.1Types of motor drives There are three ways that can be used for an electric motor to drive a Fan: 1. Belt drive 2. Direct drive 3. Gear drive
1.8.2 Types of Electric motors used to drive fans: 1. Three-phase squirrel-cage motors 2. Three-phase wounded-rotor motors 3. Single-phase, single phase induction motors 4. Single-phase, permanent-split-capacitor motors 5. Single-phase, shaded-pole motors 6. Single-phase universal motors 7. Single-phase, inside-out induction motors
1.9 FAN SPECIFICATIONS: • •
Backward Aerofoil Bladed Fan Application- Primary Air Fan
• • • • • • •
•
Power- 1500 KW Plant Capacity- 250 MW Fan size- NDZV 20 BAB2 Speed- 1000 rpm Head- 985 mmmw Pressure ~ 9850 Nm/Kg Volume – 50 m 3/s Material Used – Naxtra 70
CHAPTER 2
LITERATURE REVIEW
CHAPTER 2 LITERATURE REVIEW FINITE ELEMENT ANALYSIS (FEA) :
2.1 Introduction: Finite Element Analysis (FEA) is a computer-based numerical technique for calculating the strength and behavior of engineering structures. It can be used to calculate deflection, stress, vibration, buckling behavior and many other phenomena. It can be used to analyze either small or largescale deflection under loading or applied displacement. It can analyze elastic deformation, or "permanently bent out of shape" i.e., plastic deformation. Computer is required because of the astronomical number of calculations needed to analyze a large structure. The power and low cost of modern computers has made Finite Element Analysis available to many disciplines and companies.
2.2 Historical Background:
The very basics of the finite element method rose from the advances in aircraft. It all began with Hrenikoff, in 1941 presenting a solution to elasticity problems using “the frame work method”. This trend continued with Courant’s paper based on piecewise polynomial interpolation in 1943. Turner et al. derived stiffness matrices for truss, beam and other elements and presented their findings in 1956. But Clough first coined the term finite element in 1960.
2.3 What is FEA? The finite element analysis is a kind of analysis in which a complex region defining a continuum is discretized into simple geometric shapes called finite elements. The material properties and the governing relations are imposed on these elements and expressed in terms of unknown values at element corners. An assembly process duly considering the loading and constraints, results in a set of equations. Solution to these equations gives us the approximate behavior of the continuum.
2.4 Need for Finite Element Analysis: Finite Element Analysis makes it possible to evaluate a detailed and complex structure, in a computer, during the planning of the structure. The demonstration in the computer of the adequate strength of the structure and the possibility of improving the design during planning can justify the cost of this analysis work. FEA has also been known to increase the rating of structures that were significantly over designed and built many decades ago. In the absence of Finite Element Analysis (or other numerical analysis), development of structures must be based on hand calculations
only. For complex structures, the simplifying assumptions required to make any calculations possible can lead to a conservative and heavy design. A considerable factor of ignorance can remain as to whether the structure will be adequate for all design loads. Significant changes in designs involve risk. Designs will require prototypes to be built and field-tested. The field tests may involve expensive strain gauging to evaluate strength and deformation. With Finite Element Analysis, the weight of a design can be minimized, and there can be a reduction in the number of prototypes built. Field-testing will be used to establish loading on structures, which can be used to do future design improvements via Finite Element Analysis.
2.5 The Finite Element Method: In general, in the finite element method, a structure is broken down into many small simple blocks or elements. The behavior of an individual element can be described with a relatively simple set of equations. However, there are two general approaches associated with the finite element method. One approach called the force method uses the internal forces as the unknown constraints of the problem, while the other, the displacement method (or) stiffness method uses displacement as the unknown. In the finite element method the continuum is discretized into small inter connected elements called finite elements, and these elements have a displacement function associated with it. Each inter connected element is linked, directly (or) indirectly to every other element through common interfaces including the nodes and boundary line and surfaces. By
using using the known known stress stress strain strain proper propertie tiess of the mater material ial making making up the the stru struct cture ure,, one one can can dete determ rmin inee the the beha behavi vior or of a give given n node node in term termss of pro prope perti rties es of ever every y othe otherr in the the stru struct ctur ure. e. The The tota totall set set of equa equati tion onss desc descri ribi bing ng the the beha behavi vior or of each each node node resu result ltss in a seri series es of alge algebr brai aicc equations best expressed in matrix notation.
2.6 Concepts of FEA: As desc descri ribe bed d earl earlie ierr the the FEA FEA can can be used used to dete determ rmin inee the the stress and deflection of any structure under load. According to Newton’s II law, The force on any body due to external load is given by,
F = ma This under equilibrium conditions the above equation can be represented in the differential form as,
mä + cå + ka = 0 where, a
=
kx
å
=
dx/dt
ä
=
d2x/dt 2
So,
[m. (d2x/dt 2)] + [c. (dx/dt)] + kx = 0
In matrix form is represented as ,
[m] * [k] * [δ] = [f] By solving the above matrix equations with the values given (or) solved the values for stress and deflection can be determined easily.
2.7 General procedure for FEA: With the advent of hi-tech computers, the FEA solutions for complex problems are made easy and simple. The general procedure for the FEA is outlined in the form of a flowchart as below:
Pre – processor processor Read the input data and identify the design constraints. Model the continuum. Identify the element type and mesh the model. Define the boundary conditions and load data.
Processor/solution Compute element stiffness matrices. Assemble element equations. Solve equations for the condition Compute results.
Pre – processor processor Plot the results Interpret the results
FLOW CHART. 2.1
27.1 Discretization: It is the process by which a closed form mathematical expr expres essi sion on such such as a func functi tion on (or) (or) a diff differ eren enti tial al (or) (or) inte integr gral al equa equati tion on involving functions, all of which are viewed as having an infinite continuum of valu values es thro throug ugho hout ut some some doma domain in,, is app approxi roxima mate ted d by anal analog ogou ouss expressions that prescribes values at only a finite number of discrete points (or) volumes in the domain.
2.7.2 Meshing: A finite element model includes a mesh of nodes and elements. The best way of creating mesh is to create the part’s geometry, then generate a mesh on the geometry. Since the finite element model is associated with the part, any change to the part is automatically reflected in
the nodes and elements of the mesh. Part geometry based meshes are also used for geometry-based optimization. There are generally two types of meshes;
1.MAPPED MESH: It is a kind of mesh in which the points of the mesh are arranged in a regular way all through the continuum and can be stretched to fit a given geometry.
2.FREE MESH: It is a kind of mesh where the points fill the space to be considered but is not connected with the regular topology. The mesh with an irregular structure is often referred to as an unstructured (or) free mesh. FIG. 2.1
DIAGRAMATIC REPRESENTATION OF MAPPED AND FREE MESH
FREE MESH
MESH
2.8 Applications of FEA:
MAPPED
There are several engineering applications of FEA, but some of the notable one’s are mentioned below: Structural analysis Structural machines Aerospace engineering Solid mechanics and foundation engineering Rock mechanics and heat conduction Hydrodynamics and hydraulic engineering
Water resources and nuclear engineering.
2.9 Setting element attributes : Before generating a mesh of nodes and elements, the element attributes are to be defined. Element type Real constant set Material Properties set Element co-ordinate system
2.10 Boundary conditions: 2.10.1 Definition of Boundary condition Boundary conditions are nothing but the constraints of the model that is to be analyzed. The constraints may be displacement, inertias, loads (forces, moments), temperature, fluid velocity, etc., for every model the boundary conditions are must be specified. Without the impositions of the boundary conditions, the element and assemblage stiffness matrices, [k] and
[k], are singular; that is, their determinants vanish and their inverse do not exist. The physical significance of this is that a loaded body or structure is free to experience unlimited rigid body motion unless some supports or kinematic constraints are imposed that will ensure the equilibrium of the loads. These constraints are the boundary conditions.
2.10.2 Boundary conditions for the model 1.Displacement: The rotating motor shaft is fixed in the impeller therefore the displacement on the impeller hole is zero in all degree of freedom.
2.Angular velocity and angular acceleration: The impeller rotates about the “z” axis at a speed of 1000rpm. Therefore Angular velocity = (2πN)/60 = 104.7 rad/sec The angular acceleration is also given as 9810 rad/sec 2.
2.11 Material properties: Once a mesh has been built to describe the domain occupied by the structure, the rest of the computer model can be built. It is only at this stage that the description of the physical problem generated in the initial stage of the analysis process can be related to the computational geometry described by the mesh of nodes and elements. For each element, its material properties must be defined together with the boundary conditions on the faces of the elements, or at the nodes, which form the exterior of the mesh.
It is not necessarily straight forward task to define precisely the material properties and, frequently, they must be approximated when compiling the model data for an analysis. For this model, the constant Isotropic material has been used and their values are 1.Young’s modulus
EX = 21000 kg/mm 2
2. Density
DENS = 8.002 e-10 mN/mm 3
3. Poisson’s ratio
NUXY = 0.3
2.12 Element type Element type used in FEA may be described in terms of their shape (through the relative positions of its nodes) and degrees of freedom (possible directions of movements of each node). The element plot and nodal plot for the model are shown in fig.
ELEMENT 2-NODED BEAM ELEMENT
3 – NODED BEAM ELEMENT
3 – NODED TRIANGULAR ELEMENT
6 – NODED TRIANGULAR ELEMENT
4 – NODED AREA ELEMENT
PICTORIAL VIEW
TYPE 1-D
1–D
2–D
2–D
2–D
8 - NODED AREA ELEMENT
2–D
8 – NODED BRICK ELEMENT
3–D
4 –NODED PYRAMID ELEMENT
3–D
TABLE 2.1 ELEMENT TABLE
2.12.1 Element type for the model For this analysis 4-noded area element (SHELL 63) is used. SHELL 63 element is well suited for mapped meshing for this model. Usually for any area of a model can be meshed using 4-noded area element (SHELL 63) in a uniform manner (mapped meshing). It is a kind of mesh in which the points of the mesh are arranged in a regular way all through the continuum and can be stretched to fit a given geometry so that the results will be more accurate when compared to free mesh results.
2.12.2 Choosing the element type 1.The range of elements and testing the elements: It is not possible to present a set of universal guidelines to develop any finite element model as such structural problem and element type have their own particular features. It is not even possible to give rules for what appears in packages to be identical element types since their formulation can be different.
Any test for element behavior should be more complicated than the situation of a simple rectangular geometry with a constant load, since simple situations can give a false impression of the convergence characteristics for realistic problems. Quadratic elements, be they membrane or solid elements, give the best compromise between accuracy and efficiency for general use.
When modeling a structural problem that can be classified, as having bending deformation and the geometry is either flat or curved, then the preferred choice of elements is always the general shell element. Curved surfaces should not be modeled using flat elements as the discontinuity at element boundaries introduces significant error.
2. Using a Hierarchy of elements: Analysts should develop a model using a step by step approach. This means that they should start with a simple approximation, say a beam model, and make it more precise as the finite element modeling progresses. Never tackle a real problem directly as this is likely to be time consuming and wasteful of resources. Remember, that more results that are generated the more effort that will be necessary to check that they are reliable and relevant.
3. Restricting the dimensions of a problem: Avoid the use of solid elements to model a problem where the length in one of the spatial dimensions, for example the material thickness, is much less than the lengths in the other two dimension.
4. Plate and shell elements: Plate and shell elements have historically been the most difficult to use in terms of achieving reliable and cost effective solutions. In particular these elements in a static analysis do not give an acceptable solution if the displacement of the nodes normal to the surface of the material is greater than the thickness of the material.
5. The role of compatibility:
Elements must have the same order, all though one can mix three sided and four sided elements. There must be connection between the corner nodes of neighboring elements and, if present, continuity between the edge nodes of adjacent elements.
6. Elements of model contact: Before developing a three dimensioning model for a problem with contact between different parts, check that the package has three dimensional contact algorithms.
2.13 Fan laws and Efficiency 2.13.1 Fan laws: There are certain fan laws that are used to convert the performance of a fan from one set of variables to another.
1.Conversation of fan performance Suppose a fan of a certain size and speed has been tested and its performance has been plotted for the standard air density. We then can compute the performance of a fan of geometric similarity by converting the performance data in accordance with these fan laws without running a test on the other fan. It called as general fan laws.
2.Variation in fan speed
In order to convert the performance of a fan at one speed to another speed, We take a number of points on the performance graph and convert the corresponding data for air volume, static pressure, bhp, efficiency and noise level fro the speed of the graph to the desired speed using the following rules.
The
air
volume
(cmf)
varies
directly
with
the
speed
(cfm2/cfm1) = (rpm2/rpm1) The pressure vary as the square of the speed
(Sp2/Sp1) = (rpm2/rpm1) The brake horse power varies as the cube of the speed
(bhp2/bhp1) = (rpm2/rpm1) The efficiency remains constant but, of course, shifts to the new air
volume values. Variation in fan size
This law is used to convert the performance of one fan to another fan when they are geometrically similar . The fan laws for size , however , can be used only if the two fans are in geometric proportion . Both fans have the same number of blades . Both fans have the same blade angles and any other angles on the fan wheel and fan housing. If the diameters of the two wheels are D1 and D2 for a size ratio D2/D1, all other corresponding dimensions of wheel and housing have the same ratio.
The air volume (cfm) varies has cube of the size.
= (D2/D1)3
(cfm2/cfm1)
The pressure vary as the square of the size .
(sp2/sp1) = (D2/D1)2 The bhp varies as the fifth power of the size .
(bhp2/bhp1) = (D2/D1)5
Variation both fan size and fan speed If both the fan size D and the fan speed (rpm) are varied , the
two sets of rules discussed above can be applied consecutively , in either sequence .
(cfm2/cfm1) = (D2/D1)3 *(rpm2/rpm1) (sp2/sp1) = (D2/D1)2 *(rpm2/rpm1)2 (bhp2/bhp1) = (D2/D1)5 *(rpm2/rpm1)3 (ME2/ME1)=1 Variation in Density
This fan law is used when the fan operates at high altitude where the air density is less , where the fan handles hot or cold air (the air density is inversely proportional to the absolute temperature) , or where the fan handles a gas other than air , while the size and speed of the fan remains constant.
The air volume remains constant
(cfm2/cfm1) = 1
The pressure vary directly as the density ρ
(sp2/sp1) = (ρ2/ρ 1)
The bhp varies directly as the density ρ
(bhp2/bhp1) = (ρ2/ρ 1) The efficiency remains constant
2.13.2 Fan Efficiency
Fan work can be equated to the system resistance. Fan pressure has the dimension of work per unit volume. Thus the system resistance may also be regarded as the work required per unit volume of gas. Power kw = Q X Ps Work
= force X Distance
Power
= force X Velocity = pressure X Area X Velocity = pressure X Volume
The ratio of this air power to the power required to drive the fan is the fan efficiency. The pressure may be total (including the velocity pressure) or static and resulting efficiencies may also be “total” or “static”. Selecting a fan of higher efficiency normally results in higher first cost, but in lower operating cost.
1. Size and type limitations to good efficiency High operational efficiencies are only achievable with certain types and sizes of fan; indeed, the definition of “good” and “ high” efficiency depends on the class and quality of the fan being considered. For a particular type of fan the best efficiencie swill be achieved by higher specific speed fans of backward curved, backward inclined or aerofoil bladed design with the fans being medium or large diameter and operating at Reynolds numbers in excess of 20x10 5. Where Reynolds number = (ρuD) / μ D – Fan dameter ρ – Fluid density μ – Dynamic viscosity
2. Specification of fan requirements Aerodynamic duty: An important factor in ensuring a successful fan system is the correct specification of the fan. The starting point in the specification of the fan is
knowledge of flow rate, which the fan (or fans) is required to handle. Often there will be a range of flow rates over which the fan will be required to operate and if this range is large it may be necessary to consider employing a number of fans in parallel. The next parameter to be defined is the pressure rise required of the fan to move the gas through the system. This requires a knowledge of the layout the system including pipe lengths, pipe diameters and elevations, a knowledge of all the pipe work components in the system and information on the properties of the gas being moved, particularly its density and viscosity. From this it is possible to calculate the pressure losses in the system. If the fan duty varies with time then the use of variable geometry or variable speed is almost certainly economically beneficial in terms of whole life costs, if the duties of the fan are anticipated to increase with the time e.g. : - if the output of the process system in which the fan operates is expected to grow, then it may be possible to commence operation with a reduced diameter (or reduced width) impeller fitted in to a standard casing and, as the demand increases, fit the standard impeller. this will generally be preferable to initially running the fan at a flow rate way below its design condition and offer advantages of reduced power consumption and reduced bearing loads.
3. Estimation of fan type, size and speed: Once the flow rate and pressure are known it is possible to derive some idea of feasible options for the type of fan required. Simple formula will allow initial estimates to be made of the probable type(s) and size(s), which are optimum for a particular installation. The specific speed, Ns, of a fan is a measure of the fan shape or type.
Ns is defined as Where
Ns = [w (Q) 0.5] / (gH) 0.75
w is the rotation speed of the fan (rad / sec) Q is the volume flow rate (m 3 / sec) gH is the specific energy ( J / Kg ) gH = (p / ρ)
Where
p is the fan pressure raise – pa ρ is the fluid density – Kg / m 3
Knowing Q and gH, a range of rotational speeds can be assumed. Typically these will correspond to 2, 4, or 6 pole motor speeds with a wide choice available for belt driven fans. The value of Ns defines the optimum fan type for the duty. If Ns is less than about 1.5 the fan will be a centrifugal machine; if Ns is greater than about 2.5 the optimum fan will be an axial, between 1.5 and 2.5 the optimum unit would be mixed flow type. The next stage is to determine the approximate impeller diameter. For a centrifugal type fan the dia can be estimated from the relationship, Farrant V2 tip = gH / (0.8 - 0.23 N s) And for an axial or mixed flow machine from D = 2[ gHQ / w 3k L ]0.2 Where the loading coefficient, k L, has a value typically in the range 0.01 to 0.08. It is thus possible to get an idea of the potential speed and dia of the fan best suited to the duty. If either the speed or dia appears impractical this may well point to the need to consider multistage fans or a series of fans in parallel. For multistage fans the head per stage reduces, thus raising the specific speed per stage. For fans in parallel the flow per fan decreases thus increasing the specific speed per unit.
2.14 STRESS ANALYSIS Stress is defined as "a force tending to produce strain or tension and to change the form or dimension of a solid", by dictionary. A common man's understanding of stress is very much different from that of an engineer. For an engineer Limit Stress =
∆A
F 0 ∆A
Where, F
=
Force vector acting on the small area
M Ever since the invention of Hooks Law by the famous English Scientist Robert Hook (1935 -1703) analysis of stress and strain has attracted many brilliant scientific and engineering minds. Today, the theory is well developed and is widely used. However, a general analytical calculation for the state of stress and strain in a general solid is not yet available and is considered impossible to obtain. ' Stress analysis problems can be solved using two sets of methods, i.e. experimental and theoretical Hence, many numerical techniques have been developed and are widely used in the industries for stress analysis. Finite Element Method (FEM), one of the numerical techniques, was developed in fifties. Today Finite Element Method is very popular and widely used in industry. Though the underlying concept was originally introduced by Argyris in 1954-55, it was supplemented by Turner, Clough, Martin and Toop in 1956. The method is widely used since the development of high-speed electronic digital computers and development of numerical methods to handle difficult mathematical problems. Though the method was originally developed as a tool for structural analysis, the theory and formulation have been
progressively refined and generalized and the method has been successfully applied to many other fields like thermal, fluid, vibration, electrostatics, Electro-magnetism, etc.
2.14.1 NEED FOR STRESS ANALYSIS After the Industrial Revolution of nineteenth century, large and complex machines and structures were built to mankind. As the time passed, new types of machines and structures were built in critical and demanding applications, requiring high reliability and economy. These factors in design, under new environment of competition resulted in application of analytical methods in the solution of engineering problems. Design is no longer based upon empirical formulae. The importance of analytical methods combined with laboratory experiments in the solution of engineering problems has been recognized and accepted by the engineering community. The conflicting requirements of increased reliability, reduced cost and improved performance make the task of designer extremely complicated.Reduced cost means reduced weight. Increased reliability with reduced weight can be" achieved only on the basis of careful analysis of stress distribution in the structure and experimental investigation of the mechanical properties of the materials. Experimental techniques have become very refined over the years. Similarly, analytical techniques have become complex and advanced, leading to better understanding of stress distribution in complicated solids.
CHAPTER 3
INTRODUCTION TO ANSYS
CHAPTER 3
3.1 Introduction to ANSYS ANSYS is a general purpose finite element computer program for the solution of structural, heat transfer engineering analysis. ANSYS solution to capabilities includes: static analysis, elastic, plastic, thermal, stress, stress stiffened, large deflections, bilinear elements, dynamic analysis, model, harmonic response, linear time history, non-linear time history, heat transfer analysis: conduction, convection, radiation, coupled to fluid flow, coupled to electric flow, structures, magnetics, etc. Analysis can be made in one, two, or three dimensions, including axisymmetric and harmonic element options. ANSYS also contains a complete graphics package and extensive pre and post processing capabilities.
3.2 ANSYS offers 1.tensive capabilities 2.ailability 3.owth and development 4.pport
3.3 Examples of ANSYS analysis Examples 1.Laying ocean cable
Special options used Dynamic, stress stiffening, large deflection, hydrodynamic forces.
2.Automatic crash studies
Dynamic, large deflection, plasticity, gaps.
3.Evaluation of golf club swing
Large rotations, stress stiffening.
4.Railroad tank car
Dynamic, Fluid elements, pressure vessel fatigue evaluation.
5.Piping system evaluation
Static, seismic, gaps, large deflection.
6.Electric furnaces smelting
Heat transfer, thermal- electric elements.
7.Electronic circuit boards & microchips
8.Offshore power plant
Heat transfer, radiation, static, thermal stresses.
Multi-level sub structuring statics, modal, over 1.5 million dofs.
9.Artificial hip prosthesis
Statics, orthotropic materials.
10.Turbine Blade analysis
Stress-stiffened, modal analysis.
3.4 Choosing the software The first thing to consider is how knowledge of structural mechanics might help you and your organization. To explore this, functional area are related to structural mechanics must be considered. Structural analysis may be used to determine the linear static stress and displacement in structures such as vehicle body shell and the engine under operational loads. Also, optimization may be required to produce body shells with a given displacement for the minimum material thickness. To find out which of the available packages may be used, a list of requirements that the software should meet must be produced. More often than not, no single package will meet all the requirements, but several packages will meet some of the requirements.
3.5 Feature selection The geometry of the structures that may need to be analyzed. This will show whether a package is needed that can solve problems in two or three dimensions.
3.5.1 Coupling requirements to other software
In some cases there may be a need to link structural results to heat transfer simulations or even to fluid flow software. There may be a requirement to send the results to a proprietary post-processor or to some other display software, so that software must have interfaces.
3.5.2 The size of the simulation problem Here something about the number of nodes and elements that a typical mesh contains needs to be known, together with the number of degree of freedom that is to be calculated. This information helps to determine the storage requirements of the programs in terms of both primary and secondary storage.
3.6 Results required for analysis Stresses, strains and displacements, possibly as a function of time.
3.7 Solution speed Many things affect the time that it takes to produce the solution. Clearly, this depending on the processing speed of the hardware used, but it also depends on the structural solver itself.
3.8 Hardware availability If there is a restriction on the make or type of computer or graphics terminal that the software can be run on, this should be noted.
3.8.1 The following are some of the requirements that are related to the software Quality assurance (QA) User friendliness User support Current users
3.9 Analysis procedure 3.9.1 Static analysis A static analysis calculates the effects of steady loading conditions on a structure, while ignoring inertia and damping effects such as those caused by time varying loads. A static analysis can, however, include steady inertia loads such as gravity and rotational velocity, and time – varying loads that can be approximated as static equivalent loads (such as the static equivalent wind and seismic loads commonly defined in many building codes ).
3.9.2 Loads in a static analysis Static analysis is used to determine the displacements, stresses ,strains, and forces in structures or components caused by loads that do not induce significant inertia and damping effects.
Steady loading and response conditions are assumed that is ,the loads and the structure’s response are assumed to vary slowly with respect to time .The kinds of loading that can be applied in a static analysis include: Externally applied forces and pressures Steady- state inertial forces (such as gravity and rotational
velocity) Imposed (non-zero) displacements Temperatures (for thermal strain) Fluences (for nuclear swelling)
3.10 Procedure for a static analysis 3.10.1 The procedure for a static analysis consists of three main steps: 1.Build the model 2.Apply loads and obtain the solution 3.Review the results
The overall equilibrium equations for linear structural static analysis are: [K] {u} = {F} OR
[k] {u} = {Fq} + {Fq} N
Where: [K] = total stiffness matrix = ∑
[K e]
M=1
{u} = nodal displacement vector N
= number of elements
[Ke] = element stiffness matrix {Fq} = total applied load vector {Fr} = reaction load vector
1.Build the model: To build the model, define the element types, element real constants, material properties, and the model geometry.
2.Apply loads and obtain the solution: In this step, the loads (boundary conditions) are defined and the solution is obtained.
3.Review the results: After the solution is completed, the post-processing step gives the results of the static analysis.
Primary data available Nodal displacements (UX, UY, UZ, ROTX, ROTY,
ROTZ) Derived data available Nodal and element stresses Nodal and element strains Element forces Nodal reaction forces
Etc.,
3.11 Modal analysis Modal analysis is used to determine the vibration characteristics (natural frequencies and mode shapes) of a structure or a machine component while it is being designed. it also can be a starting point for another, more detailed, dynamic analysis, such as a transient dynamic analysis, a harmonic response analysis, or a spectrum analysis.
3.11.1 Uses of modal analysis Modal analysis is used to determine the natural frequencies and mode shapes of a structure. The natural frequencies and mode shapes are important parameters in the design of a structure for dynamic loading conditions. Modal analysis can be made on a pre-stressed structure, such as spinning turbine blade. Another useful feature is modal cyclic symmetry, which allows you to review the mode shapes of cyclically symmetric by modeling just a sector of it.
3.12 Procedure for modal analysis 3.12.1 The procedure for a modal analysis consists of four main steps: 1. Build the model 2. Apply the loads and obtain the solutions 3. Expand the modes 4. Review the results
3.12.2 Assumptions and restrictions Valid for structural and fluid degrees of freedom(DOFs) The structure has constant stiffness and mass effects. There is no damping.
The structure has no time varying forces, displacements, pressures, or
temperature applied (free vibration). The equation of motion for an undamped system, expressed in matrix
notation using the above assumptions is: [M] {u} + [K] {u} = {0}
3.13 Design optimization Design optimization is a technique that seeks to determine an optimum design. By “optimum design” all the specified requirements are met with a minimum expense of certain factors such as weight, surface area, volume, stress, cost, etc. in other words, the optimum design is usually one that is as effective as possible. Any aspect of the design can be optimized: dimensions (such as thickness), shape (such as fillet radii), placement of supports, and cost of fabrication, natural frequency, material property and so on. An optimum design can be defied as the best possible design satisfying a specific objective and a set of constraints imposed by the specifications or by the design problem itself.
3.14 Typical examples of optimized designs are: Design of aircraft, aerospace and automotive structures for
minimum weight. Design of machines, components, frames, and mechanisms,
handling devices etc., for minimum cost. Design of pumps, turbines, compressors, engines, and etc.,
for maximum efficiency.
CHAPTER 4
METHODOLOGY
CHAPTER 4 METHODOLOGY
4.1. Solid model generation using preprocessor: In ANSYS there are three stages. They are pre processor, solution and post processor. So before doing analysis, the geometry of the model should be created. Modeling is done in ANSYS through pre-processor. There we have lot of option through which the geometry of the model is created.
4.2. Meshing contours: After generation of the solid model using pre processor, the model should be meshed properly. That is the model should be disecritised into number of small elements. For meshing of the model, we should generate meshing contours. That is the lines of the geometry should be properly divided. So that we can easily mesh the model otherwise without the contours the mesh won’t be proper and we can’t solve it.
4.3. Meshing of areas: After generation of contours for proper meshing we should go for meshing of the model. There are two types of meshing. They are free mesh and mapped mesh. So in free mesh we can solve it and get the results but it won’t be accurate. So for accurate results, we have to go for mapped mesh. So if we did line element sizing (lesize) properly we get mapped mesh.
4.4. Defining material: So after completing modeling and meshing we have to define the material of the model. So there are different properties which will define a material that is density, young’s modulus, Poisson’s ratio. For different materials this values are different. By using these properties the material can be define in pre-processor.
4.5. Choosing appropriate element for analysis: The basic concept of FEA is to discritise the model into finite number of smaller elements. There are different element types available in ANSYS pre-processor. Based on the model the element types vary. We have to choose a appropriate element for analysis.
4.6. Attributing equivalent and actual boundary: After discritising and defining material of a model, we have to apply the boundary conditions and the loads wherever we required for the analysis. First, constraints should be applied. So wherever required, the degrees of freedom should be arrested. After applying constraints, the loads are applied on nodes or element for the analysis.
4.7. Solving the problem using solver: Solution is the second stage in ANSYS where the solution of the given problem is done. So here we won’t do anything the solution module generate the element matrices and find the stress and deflections according to the parameters we applied.
4.8. Viewing results: The results are viewed in post-processor. Where the stress and deflection can be plotted on the screen. So different colours are plotted for different stress value. We can view both the maximum and minimum stress.
4.9. Studying the parameters stress and deflection for existing design: The above steps are done for the original design and stress value and deflection for original design can be studied.
4.10. Modifying the geometry model by reducing the thickness: After studying the stress and deflection for original design. The stress and deflection for modified design should be studied. The design is modified by reducing the thickness. Then all the above steps followed for finding the stress and deflection value. Finally the results of the original and modified design should be should be compared in order to obtain a optimized design.
CHAPTER 5
MODELING
CHAPTER 5 MODELING 5.1 SEGMENT GENERATION: First the segment of the radial fan impeller is created using ANSYS preprocessor .The created segment is shown below in fig 1.
Area plot for the created segment using ANSYS preprocessor is shown in the fig 2
5.2 REAL CONSTANTS FOR THE MODEL:
COMPONENT
ORIGINAL REAL CONSTANT VALUES (mm) 25
MODIFIED REAL CONSTANT VALUES (mm) 18
15
10
5
3.15
COVERPLATE
12
8
RING
30
15
FLANGE
80
45
BACKPLATE (BOTTOM) BACKPLATE (TOP) BLADE
The table 5.1 shows the real constants for various components of the original and optimized fan impeller model.
Thicknesses of the various component of impeller are ploted in different colours which is shown in fig 3.
A1- Back Plate (Bottom) A2- Back Plate (Top) A3- Bade A4-Cover Plate A5- Ring A6- Flange
5.3 MAPPED MESH:
Mapped mesh is generated for the model which is shown in fig 4.
Element type used for meshing the model is SHELL ELEMENT (ET, 1, 63).
5.4 GENERATION OF FAN IMPELLER: Fan Segment created is copied to 360 degrees along yaxis with 12 segments (including original) so the fan impeller model is generated which is shown in fig 6
5.5 BOUNDARY CONDITION: DISPLACEMENT: The rotating motor shaft is fixed in the impeller therefore displacement on the impeller hole is zero in all degree of freedom.
ANGULAR ACCELERATION:
VELOCITY
AND
ANGULAR
The impeller rotates about the z-axis at a speed of 1000 rpm.Therefore angular velocity=2∏n/60=104.7 rad/sec(105) Angular acceleration also 9810 rad/sec 2.
5.6 SOLUTION: After completing modeling and giving boundary conditions the problem has to be solved using the ANSYS-SOLUTION utility.In the solution utility all the element matrices are formed and it is solved to find the stress and deflection for the applied boundary condition.
CHAPTER 6
RESULTS AND DISCUSION
CHAPTER 6 RESULTS AND DISCUSSIONS
6.1 STATIC ANALYSIS: The stress distribution and the deflection of the impeller are found. The stress distribution and the deflection plot for the various components of the impeller are plotted in the figures.
6.2 OPTIMIZATION: For the original fan impeller the stress value is 4.274kgf/mm2 and deflection is .0678mm.The blade in the impeller has the maximum stress of 4.274kgf/mm2.
COMPONENTS FAN IMPELLER BACKPLATE (BOTTOM) BACKPLATE (TOP) BLADE COVER PLATE RING FLANGE
ORIGINAL FAN OPTIMIZED FAN STRESS DEFLECTION STRESS DEFLECTION Kgf/mm 2 4.274 1.284
0.0678 0.0126
Kgf/mm 2 5.822 1.291
0.09945 0.016396
2.318
0.03426
2.593
0.041143
4.274 2.852 2.927 .58453
0.0678 0.0526 .04845 .00198
5.822 3.091 3.159 .681387
0.099455 0.064076 0.057363 .002394
mm
mm
TABLE .6.1
6.3 RESULTS FOR FAN IMPELLER WITH ORIGINAL THICKNESS:
6.4 RESULTS FOR OPTIMIZED FAN IMPELLER:
CHAPTER 7
CONCLUSION
CHAPTER 7 CONCLUSION
In this work, an attempt has been made to increase the Fan efficiency by optimizing the thickness of the various components in the fan impeller, and analyzing the stress distributions in them. Optimization of the thickness of the parts of impeller leads to decrease in weight of the Fan Impeller, and in turn the power required for driving the fan decreases. Pre -stress conditions are applied to this model, therefore the strengthening and weakening of the impeller is predicted.
7.1. DIMENSIONS FOR THE MODEL:
COMPONENT
ORIGINAL IMPELLER THICKNESS (mm) 25
OPTIMIZED IMPELLER THICKNESS (mm) 18
Back plate (Bottom) Back plate (To p) Blade
15
10
5
3.15
Cover plate
12
8
Ring
30
15
Flange
80
45
TABLE.7.1
7.2 WEIGHT REDUCTION: After optimizing the thickness of the Fan impeller the weight of the Fan Impeller is reduced. Existing weight of the Fan Impeller=10 tones =10,000 kg
After optimizing % of weight reduced in the
=18.5%
Fan Impeller
Amount of weight saved
= (18.5/100)*10,000 = 1850 kg. = 1.85 tones
Cost of steel/kg
= Rs.300
In the BHEL-RANIPET there are about 12 Fans made per year. Total cumulative weight saved
= 12*1850 = 22200 kg = 22.2 tones
Total cumulative cost saved per year = 22200*300 = Rs. 66,60,000
REFERENCES
