AVIATION, AEROSPACE AND TECHNOLOGY FESTIVAL ...Figure 3.16 Equivalent Stress Distribution at 115200 RPM (isometric view) ..... 46 Figure 3.17 Equivalent Stress Distribution at 115200

TEKNOFEST İSTANBUL

AVIATION, AEROSPACE AND TECHNOLOGY

FESTIVAL

MINI JET RADIAL COMPRESSOR DESIGN

COMPETITION

CRIRICAL DESIGN REPORT

TEAM NAME: MAX-THRUST

TEAM MEMBERS:

Yahya GENCER

Halil İbrahim AYDIN

ADVISOR: Dr. Mehmet Numan KAYA

JUNE 2019

IV

TABLE OF CONTENTS

TABLE OF CONTENTS .................................................................................................................................... IV

LIST OF FIGURES ........................................................................................................................................... VI

LIST OF TABLES ............................................................................................................................................. VI

LIST OF CHARTS ............................................................................................................................................ IX

GROUP SCHEMA ............................................................................................................................................ X

INTRODUCTION ............................................................................................................................................. 1

1. PROJECT OBJECTIVE ................................................................................................................................... 1

2. COMPUTATIONAL FLUID DYNAMICS (CFD) RESULTS .................................................................................. 2

2.1. INTRODUCTION ............................................................................................................................................. 2 2.2. MESH REPORT .............................................................................................................................................. 2 2.3. DOMAIN AND BOUNDARY PHYSICS .................................................................................................................... 3 2.4. NUMERICAL RESULTS (DESIGN POINT) ............................................................................................................... 9

2.4.1. Pressure Ratio, Isentropic Efficiency, Mass Flow Rate ...................................................................... 9 2.4.2. Surge Margin .................................................................................................................................. 10 2.4.3. Compressor Map ............................................................................................................................. 12 2.4.4. Required parameters versus obtained parameters ........................................................................ 14 2.4.5. Detailed Summary .......................................................................................................................... 15 2.4.6. Charts .............................................................................................................................................. 16 2.4.7. Figures ............................................................................................................................................ 18 2.4.8. Streamwise Charts .......................................................................................................................... 21 2.4.9. Blade Geometry Figures .................................................................................................................. 23

2.5. NUMERICAL RESULTS (OFF-DESIGN POINT)....................................................................................................... 27 2.5.1. Pressure Ratio, Isentropic Efficiency, Mass Flow Rate .................................................................... 27 2.5.2. Surge Margin .................................................................................................................................. 28 2.5.3. Required parameters versus obtained parameters ........................................................................ 30 2.5.4. Detailed Summary .......................................................................................................................... 30 2.5.5. Mesh Independency ........................................................................................................................ 32

3. STRUCTURAL............................................................................................................................................ 33

3.1. MATERIAL PROPERTIES ................................................................................................................................. 33 3.2. STRUCTURAL ANALYSIS ................................................................................................................................. 34

3.2.1. Meshing .......................................................................................................................................... 34 3.2.2. Steady-State Thermal ..................................................................................................................... 36 3.2.3. Static Structural .............................................................................................................................. 39 3.2.4. Results ............................................................................................................................................. 41

4. VIBRATION .............................................................................................................................................. 50

4.1. MODAL ANALYSIS ........................................................................................................................................ 50 4.2. REQUIREMENTS ........................................................................................................................................... 51 4.3. ANALYSIS FOR BLISK ..................................................................................................................................... 52 4.4 ANALYSIS FOR BLADES ................................................................................................................................... 54

5. BALANCE (DENGELEME)(REFERANS) ........................................................................................................ 57

6. ASSEMBLY (MONTAJ) .............................................................................................................................. 60

7. PRODUCUBILITY ....................................................................................................................................... 61

8. CAD MODEL AND GEOMETRY .................................................................................................................. 63

8.1. MODELING OF IMPELLER ............................................................................................................................... 63 8.2. GEOMETRIC PROPERTIES ............................................................................................................................... 66

V

8.3. TECHNICAL DRAWING ................................................................................................................................... 67 8.4. MASS OF THE IMPELLER ................................................................................................................................ 67

9. CONCLUSION ........................................................................................................................................... 68

REFERENCES ................................................................................................................................................ 69

APPENDIX A : TECHNICAL DRAWING OF THE CAD MODEL ........................................................................... 70

VI

LIST OF FIGURES

Figure 2.1. Different view of the mesh and Boundary Layer Refinement Control ................ 3 Figure 2.2. y+ value of the different locations ....................................................................... 3 Figure 2.3. Surge Margin Estimation .................................................................................... 10 Figure 2.4. Compressor Map................................................................................................. 12

Figure 2.5. A picture from the parametric study window which were taken after completing

the CFD analysis to draw the compressor map ...................................................................... 13 Figure 2.6. Stage 1 contours of circumferentially area-averaged meridional velocity ......... 18 Figure 2.7. Stage 1 contours of circumferentially area-averaged relative Mach number ..... 18 Figure 2.8. Stage 1 contours of relative Mach number at 10% span .................................... 18

Figure 2.9. Stage 1 contours of relative Mach number at 50% span .................................... 18 Figure 2.10. Stage 1 contours of relative Mach number at 90% span ........................... 19 Figure 2.11. Stage 1 contours of relative total pressure at 10% span ................................... 19 Figure 2.12. Stage 1 contours of relative total pressure at 50% span .............................. 19 Figure 2.13. Stage 1 contours of relative total pressure at 90% span ................................... 19

Figure 2.14. Stage 1 contours of circumferentially area-averaged static pressure ......... 20 Figure 2.15. Stage 1 velocity vectors at 10% span ............................................................... 20

Figure 2.16. Stage 1 velocity vectors at 50% span ............................................................... 20 Figure 2.17. Stage 1 velocity vectors at 90% span ............................................................... 20 Figure 2.18. Isometric 3D View of the Blade, Hub and Shroud ....................................... 23 Figure 2.19. Meridional View of the Blade, Hub and Shroud .............................................. 23

Figure 2.20. Mesh elements at %50 span.............................................................................. 23 Figure 2.21. Contour of M rel at 20% Span .......................................................................... 23

Figure 2.22. Contour of M rel at 50% Span .......................................................................... 24 Figure 2.23. Contour of M rel at 80% Span .......................................................................... 24 Figure 2.24. Velocity Vectors at 20% Span .......................................................................... 24

Figure 2.25. Velocity Vectors at 50% Span .......................................................................... 24 Figure 2.26. Velocity Vectors at 80% Span .......................................................................... 25

Figure 2.27. Vector of Area Averaged Cm on Meridional Surface .................................... 25 Figure 2.28. Contour of P at Blade LE ................................................................................. 25

Figure 2.29. Contour of M rel at Blade LE ........................................................................... 25 Figure 2.30. Contour of P at Blade TE ................................................................................. 26 Figure 2.31. Contour of M rel at Blade TE ........................................................................... 26

Figure 2.32. Velocity Streamlines at Blade TE .................................................................... 26 Figure 2.33. Location of the estimated Surge Margin .......................................................... 29

Figure 2.34. Mesh Independecy Study Pressure Ratio vs. Number of Mesh ....................... 32

Figure 3.1 Ansys Workbench For Structural Analysis ......................................................... 34

Figure 3.2 Mesh View ........................................................................................................... 36 Figure 3.3 Convection On Fluid Surface .............................................................................. 37 Figure 3.4 Convection On Back-Face ................................................................................... 37 Figure 3.5 Temperature Condition On Front Surface ........................................................... 38

Figure 3.6 Temperature Condition On Back-Face ................................................................ 38 Figure 3.7 Imported Body Temperature ............................................................................... 39 Figure 3.8 Variable Pressure Load ........................................................................................ 40

Figure 3.9 Rotational Velocity Condition ............................................................................. 40 Figure 3.10 Fixed Support Condition ................................................................................... 41 Figure 3.11 Equivalent Stress Distribution at 96000 RPM (isometric view) ....................... 42 Figure 3.12 Equivalent Stress Distribution at 96000 RPM (back view) ............................... 42 Figure 3.13 Equivalent Stress Distribution at 96000 RPM (section view) ........................... 43

VII

Figure 3.14 Total Deformation Distribution at 96000 RPM (isometric view) ..................... 44

Figure 3.15 Total Deformation Distribution at 96000 RPM (back view) ............................. 45

Figure 3.16 Equivalent Stress Distribution at 115200 RPM (isometric view) ...................... 46 Figure 3.17 Equivalent Stress Distribution at 115200 RPM (back view) ............................. 47 Figure 3.18 Equivalent Stress Distribution at 115200 RPM (section view) ......................... 47 Figure 3 19 Equivalent Stress Distribution at 110000 RPM (isometric view) ...................... 48 Figure 3.20 Equivalent Stress Distribution at 110000 RPM (back view) ............................. 49

Figure 3.21 Equivalent Stress Distribution at 110000 RPM (section view) ......................... 49 Figure 3.22 Ansys Workbench For Modal Analysis............................................................. 50 Figure 3.23 An Example of Campbell Diagram ................................................................... 51 Figure 3.24 Campbell Diagram For Blisk Structure ............................................................. 52 Figure 3.25 Geometry of Blades For Modal Analysis .......................................................... 54

Figure 3.26 Fixed Support Surfaces ...................................................................................... 54 Figure 3.27 Campbell Diagram For Blade Structure ............................................................ 55

Figure 5.1 General view of the balance locations ................................................................. 57 Figure 5.2 Permissible residual specific unbalance based on balance quality grade G and

service speed n ....................................................................................................................... 59

Figure 6.1. ISO ALISTIRMA TABLOSU............................................................................ 60

Figure 7.1. Angle and Thickness Layer Control ................................................................... 61 Figure 7.2. Blade geometry ................................................................................................... 62

Figure 8.1 Compressor Tip Profile Sizes [2] ........................................................................ 64 Figure 8.2 Rake angle (Vista CCD Help) ............................................................................. 65

Figure 8.3 Isometric (a), left (b) and front (c) views of the impeller. ................................... 66

VIII

LIST OF TABLES

Table 1.1. Main Objectives ..................................................................................................... 1

Table 2.1. Mesh Information for TFF ..................................................................................... 2 Table 2.2. Mesh Statistics for TFF .......................................................................................... 2 Table 2.3. y+ value of the different locations ......................................................................... 3

Table 2.4. Domain Physics ...................................................................................................... 4 Table 2.5. Boundary Physics for TFF ..................................................................................... 5 Table 2.6. Design Point Requirements .................................................................................... 9 Table 2.7. Performance Results............................................................................................... 9 Table 2.9. Performance Results............................................................................................. 27

Table 2.10. Design Points Analyzes Results ......................................................................... 28 Table 2.11. Surge Point Analaysis Results for Off-Design Point ......................................... 29 Table 2.12. Comparison of the Required and CFD Results for the Design Point ................. 30

Table 2.13. Summary Data Table for Off-Design Point ....................................................... 31 Table 2.14. Mesh Independecy Data ..................................................................................... 32

Table 3.1 Properties of Aluminum 2124 Alloy ..................................................................... 33 Table 3.2 Thermal Conductivity Values ............................................................................... 33 Table 3.3 Mesh Properties ..................................................................................................... 35

Table 3.4 Ambient Temperature Values For Convection Fluid Surface............................... 36 Table 3.5 Yield Strenth Requirement and Analysis Result ................................................... 44

Table 3.6 Natural Frequency Values For Blisk Structure ..................................................... 53 Table 3.7 Natural Frequency Values For Blade Structure .................................................... 56

Table 5.1 Balance quality grade ............................................................................................ 58

Table 8.1 Impeller Geometric Properties (Vista CCD) ......................................................... 66

Table 8.2 Impeller Properties ................................................................................................ 67

IX

LIST OF CHARTS

Chart 2.1. Row1 blade loading chart .................................................................................... 16 Chart 2.2. Row1 chart showing circumferentially averaged flow angle at the LE............... 16 Chart 2.3. Row1 chart showing circumferentially averaged flow angle at the TE............... 16 Chart 2.4. Row1 chart showing circumferentially averaged relative and absolute Mach

number at the TE .................................................................................................................... 16 Chart 2.5. Row1 chart showing circumferentially averaged Cm at the TE .......................... 17 Chart 2.6. Row1 chart showing circumferentially averaged relative Mach number at the LE

................................................................................................................................................ 17 Chart 2.7. Chart showing streamwise, area averaged relative Mach number versus averaged

normalized M. ........................................................................................................................ 17 Chart 2.8. Streamwise Plot of Pt and P................................................................................. 21

Chart 2.9. Streamwise Plot of Tt and T ................................................................................ 21 Chart 2.10. Streamwise Plot of Absolute and Relative Mach Number ................................ 21 Chart 2.11. Spanwise Plot of Relative Mach Number at LE ................................................ 21 Chart 2.12. Spanwise Plot of Relative Mach Number at TE ............................................... 22

Chart 2.13. Spanwise Plot of Absolute Mach Number at TE ............................................... 22 Chart 2.14. Spanwise Plot of Meridional Velocity at TE ..................................................... 22

X

GROUP SCHEMA

Team Members Task in the Project Education Level

Yahya GENCER

• Structural analysis

• Vibration analysis

• Burst speed

Senior Student at Necmettin

Erbakan University

Halil İbrahim AYDIN

• CAD Model and Geometry

• Technical Drawing

• Design point and off-design CFD

Analysis

Senior Student at Necmettin

Erbakan University

1

INTRODUCTION

This work is a critical design report about designing a radial impeller. This report consists of

nine main sections. In the 1st section, the objectives of this project were explained. Numerical

results, compressor map and surge margin were examined in the 2nd section. 3rd and 4th parts

cover structural and vibration analysis results. In Section 5, balance and residual balance grade

were calculated according to reference document. The required calculations and the tolerances

were examined for the proper assembly in section 6. Producibility of the blades were explained

in section 7. CAD model, Geometry and Technical Drawing are explained in Section 8.

Conclusion and some comments were made in the last section. Also, technical drawing can

be found in the Appendix A.

1. PROJECT OBJECTIVE

In this project, our goal is to design a radial impeller which has a specific pressure ratio and

efficiency for a micro gas turbine engine which is used in UAV and missile applications.

Initially, a detailed literature survey was conducted to gather information about the studies in

the field. For this study, the main objectives were given in Table 1.1.

Table 1.1. Main Objectives

ROTATIONAL SPEED 96000 RPM

MASS FLOW RATE 0.68 kg/s

PRESSURE RATIO 4.6

ISENTROPIC EFFICIENCY ≥87%

WEIGHT ≤260 g

2

2. COMPUTATIONAL FLUID DYNAMICS (CFD) RESULTS

2.1. Introduction

This report summarizes the results of the CFD analysis performed to design a centrifugal

compressor according to the given objectives. In the following sections both quantitative and

qualitative results were presented in the form of tables, charts and figures.

The figures show blade-to-blade contours and vector views, circumferentially averaged

meridional views, streamwise mass or area averaged quantities from the inlet to the outlet of

the full machine.

Mesh information and mesh statistics were also listed. Boundary conditions, method used in

analysis and all the other information used in SETUP part were shown. ANSYS CFX 18.2

was employed to conduct the CFD analysis and the results were shown below in figures and

charts. Performance results such as pressure ratio, isentropic efficiency, mass flow rate and

velocity, density, Mach number, pressure and all the other parameters are shown in the tables.

Compressor map is drawn by the help of ANSYS Turbo Setup.

2.2. Mesh Report

Firstly, a grid independency study was made by chaning the mesh element numbers

from 100.000 to 1.500.000 to obtain more accurate results. The grid with 324.133 was found

to be suitable for the study and this was shown in detail in the section 2.5.5. In mesh

independency section, results were shown with respect to element number. Mesh information,

number of nodes and elements, mesh qualities (max-edge length ratio etc.) were listed in the

tables below.

Table 2.1. Mesh Information for TFF

Domain Nodes Elements

Row1 349710 324133

Table 2.2. Mesh Statistics for TFF

Domain Maximum Edge

Length Ratio

Minimum Face

Angle

Maximum

Face Angle

Maximum

Element

Volume Ratio

Minimum

Volume

Maximum

Connectivity

Number

Row1 890.724 14.1944 [degree]

165.87 [degree]

16.8269 3.8944*10^-16

10

3

Figure 2.1. Different view of the mesh and Boundary Layer Refinement Control

Figure 2.2. y+ value of the different locations

Table 2.3. y+ value of the different locations

y+ values

Shroud 1.7771

Main Blade 2.2577

Splitter Blade 2.87

Hub 0.989

2.3. Domain and Boundary Physics

Domain and boundary physics were presented in Table 2.4 and 2.5, respectively. All

the information such as angular velocity, method used in analyzes (SST), boundary conditions

at inlet (total pressure=101325 Pa and Total temperature 288.15 K) and outlet (mass flow

rate=0.68 kg/s) and the other conditions (interface etc.) were listed in these tables.

4

Table 2.4. Domain Physics

Domain - Row1

Type Fluid

Location Row1 Passage

Materials

Air Ideal Gas

Fluid Definition Material Library

Morphology Continuous Fluid

Settings

Buoyancy Model Non Buoyant

Domain Motion Rotating

Alternate Rotation Model true

Angular Velocity orientation * baseSpeed * percentSpeed / 100.0

Axis Definition Coordinate Axis

Rotation Axis Coord 0.3

Reference Pressure 0.0000e+00 [Pa]

Heat Transfer Model Total Energy

Include Viscous Work Term On

Turbulence Model SST

Turbulent Wall Functions Automatic

High Speed Model On

Domain Interface - Row1 Periodic

Boundary List1 Row1 Periodic Side 1

Boundary List2 Row1 Periodic Side 2

Interface Type Fluid Fluid

Settings

Interface Models Rotational Periodicity

Axis Definition Coordinate Axis

Rotation Axis Coord 0.3

Mesh Connection Automatic

5

Table 2.5. Boundary Physics for TFF

Domain Boundaries

Row1 Boundary - Row1 Inlet

Type INLET

Location Row1 INBlock INFLOW

Settings

Flow Direction Cylindrical Components

Unit Vector Axial Component inlet axial compt

Unit Vector Theta Component inlet tangential compt

Unit Vector r Component 0.0000e+00

Flow Regime Subsonic

Heat Transfer Stationary Frame Total Temperature

Stationary Frame Total

Temperature

2.8815e+02 [K]

Mass And Momentum Stationary Frame Total Pressure

Relative Pressure 1.0132e+05 [Pa]

Turbulence Medium Intensity and Eddy Viscosity Ratio

Boundary - Row1 Periodic Side 1

Type INTERFACE

Location Row1 INBlock PER1, Row1 OUTBlock PER1, Row1

Passage PER1

Settings

Heat Transfer Conservative Interface Flux

Mass And Momentum Conservative Interface Flux

Turbulence Conservative Interface Flux

Boundary - Row1 Periodic Side 2

Type INTERFACE

Location Row1 INBlock PER2, Row1 OUTBlock PER2, Row1

Passage PER2

Settings

Heat Transfer Conservative Interface Flux

Mass And Momentum Conservative Interface Flux

Turbulence Conservative Interface Flux

Boundary - Row1 Outlet

Type OUTLET

Location Row1 OUTBlock OUTFLOW

6

Settings

Flow Regime Subsonic

Mass And Momentum Mass Flow Rate

Mass Flow Rate massflow

Mass Flow Rate Area Total for All Sectors

Mass Flow Update Shift Pressure

Pressure Profile Blend 9.5000e-01

Pressure Profile Shape 0.0000e+00 [Pa]

Boundary - Row1 Blade1

Type WALL

Location Row1 Blade 1

Settings

Heat Transfer Adiabatic

Mass And Momentum No Slip Wall

Wall Roughness Smooth Wall

Boundary - Row1 Blade2

Type WALL

Location Row1 Blade 2

Settings




Boundary - Row1 Hub

Type WALL

Location Row1 Passage HUB

Settings




Boundary - Row1 Hub0

Type WALL

Location Row1 INBlock HUB

7

Settings




Boundary - Row1 Hub2

Type WALL

Location Row1 HUB DOWNSTREAM, Row1 OUTBlock HUB

Settings



Wall Velocity Counter Rotating Wall


Boundary - Row1 Shroud

Type WALL

Location Row1 Passage SHROUD

Settings





Boundary - Row1 Shroud0

Type WALL

Location Row1 INBlock SHROUD

Settings





Boundary - Row1 Shroud2

Type WALL

Location Row1 OUTBlock SHROUD, Row1 SHROUD DOWNSTREAM

Settings



8



9

2.4. Numerical Results (Design point)

This section gives information about performance results (mass flow rate, rotational

speed, total pressure ratio, isentropic efficiency etc.).

2.4.1. Pressure Ratio, Isentropic Efficiency, Mass Flow Rate

The requirements were given in Table 2.6 and this table was taken from the Ref. [2].

Table 2.6. Design Point Requirements

Table 2.7 summarizes the performance results and it can be seen that mass flow rate, total pressure ratio and isentropic efficiency were obtained as required.

Table 2.7. Performance Results

Rotational Speed 10053.1000* [radian s^-1]

Tip Diameter 0.0992 [m]

Tip Speed 498.7700 [m s^-1]

Mass Flow Rate 0.6898* [kg s^-1]

Power 127806.0000 [W]

Inlet Flow Coefficient 0.1148

Total Pressure Ratio 4.5877*

Total Temperature Ratio 1.6399

Total-to-Total Isentropic Efficiency % 88.3875*

Total-to-Total Polytropic Efficiency % 90.5994

Polytropic Head 167855.0000 [J kg^-1]

Polytropic Head Coefficient 0.6747

Diffuser Loss Coef., Y2 0.0685



Diffuser Cp 0.2597

*Requested parameters are shown bold.

10

2.4.2. Surge Margin

Requirement: Surge margin value of the compressor shall be either equal to or greater

than 15.

Pressure ratio vs mass flow rate graph was drawn according to analyzes results.

Different mass flow rate values were defined as the outlet boundary condition and the results

were listed below. When the mass flow rate decreases, pressure increases till some point

(surge point). After that, it begins to decrease while mass flow rate decreases.

Figure 2.3. Surge Margin Estimation

Note: Surge point should be located where the pressure is the maximum. But, the pressure

ratio may vary with respect to mesh number. That is, we are lack of some high capability computers

to eliminate this problem. Decreament of the pressure ratio is much higher at m=0.55 kg/s than the

others. That is why we chose the surge point at m=0.55 kg/s.

Table 2.7. Surge Point Analaysis Results for Design Point

Surge Point Analysis Results

Mass Flow Rate 0,55 kg/s

Pressure Ratio 4,496

Isentropic Efficiency %82,02

Base Speed 96000 rpm

Percent Speed %100

11

**Surge margin value should be found by means of the below-given formula.

PRt-t/stall: Total pressure ratio at Stall/Surge point

PRt-t/tas.: Total pressure ratio at Design point

ṁt-t/stall: Air flow rate (kg/s) at Stall/Surge point

ṁt-t/tas.: Air flow rate (kg/s) at Design point

PRt-t/stall = 4,496 ṁt-t/stall = 0,55 kg/s

PRt-t/tas = 4,5877 ṁt-t/tas = 0,689

Surge margin calculation for the current study:

( 4,496

4,5877∗

0,689

0,55− 1) ∗ 100 = 𝟐𝟐, 𝟕𝟔

12

2.4.3. Compressor Map

To draw the compresor map of the designed radial impeller, ANSYS CFX is used

together with the ANSYS parametric study module. The analyzes were made at different

rotational speeds and massflow rates to plot the compressor map. In Fig 2.4, compressors

maps for different rotational speeds were given. At each rotational speed, generally,

simulations were made for 6 massflow rate values and simulations took approximately 12

hours for each speed line. In Fig. 2.5, a Picture from the parametric study section of the

ANSYS was given.

Figure 2.4. Compressor Map

13

Figure 2.5. A picture from the parametric study window which were taken after completing

the CFD analysis to draw the compressor map

14

2.4.4. Required parameters versus obtained parameters

Table 2.8. Comparison of the Required and CFD Results for the Design Point

Required CFD

Results

Unit Is the Condition Met?

Mass Flow Rate 0,67 ≤ 𝑚 ≤ 0,69 0,6898 𝑘𝑔/𝑠 YES

Isentropic Efficiency % ≥ 87 88,3875 - YES

Total Pressure Ratio 4,55 ≤ 𝜋 ≤ 4,65 4,5877 - YES

Surge Margin ≥ 15 22,76 - YES

In the Table 2.9, mass flow rate can be seen for the Row1 Inlet and Row1 Outlet. Mass

flow rate at the Row1 Inlet equals to 0,0985 kg/s. We have 7 blade which means 7*0,0985

= 0,689 kg/s for the whole impeller. The minus sign at the Row1 Outlet means the mass flow

rate leaves the impeller.

Table 2.9. Boundary Flows for TFF

Location Type Mass Flow Momentum

X Y Z

Row1 Blade1 Boundary 0.0e+00 2.14e+01 1.65e+01 1.93e+01

Row1 Blade2 Boundary 0.0e+00 2.10e+01 -1.32e+00 9.66e+00

Row1 Hub0 Boundary 0.0e+00 1.52e+01 -1.23e+01 -2.53e-02

Row1 Hub2 Boundary 0.0e+00 -4.52e-01 7.42e-02 -2.27e+02

Row1 Hub Boundary 0.0e+00 2.63e+01 -7.80e+01 -1.68e+02

Row1 Inlet Boundary 9.85e-02 3.90e-03 1.89e-02 6.03e+01

Row1 Outlet Boundary -9.85e-02 -5.91e+01 1.33e+02 3.24e+00

Row1 Shroud0 Boundary 0.0e+00 -5.53e+01 1.87e+01 -7.82e-02

Row1 Shroud2 Boundary 0.0e+00 -3.33e-01 -8.95e-02 1.96e+02

Row1 Shroud Boundary 0.0e+00 -1.06e+02 1.23e+02 1.07e+02

15

2.4.5. Detailed Summary

The table below gives a summary of the mass or area averaged solution variables and

derived quantities computed at the inlet, leading edge (LE Cut), trailing edge (TE Cut) and

outlet locations. The flow angles are measured with respect to the axial direction.

Table 2.10. Row1 Summary Data Table

Quantity Inlet LE Cut TE Cut Outlet Units TE-LE Units

Density 1.0579 0.9867 2.3016 2.6222 [kg m^-3] N/A [kg m^-3]

P 82590.5 76142.8 263274.0 323836.0 [Pa] 187131.0 [Pa]

P0 (abs) 101283.0 101725.0 496488.0 464651.0 [Pa] 394763.0 [Pa]

P0 (rel) 101111.0 99501.4 94675.4 90971.8 [Pa] -4825.95 [Pa]

T 271.911 264.235 391.4030 422.936 [K] 127.168 [K]

T0 (abs) 288.244 288.775 473.5140 472.704 [K] 184.739 [K]

T0 (rel) 288.104 288.116 291.4930 295.183 [K] 3.3769 [K]

H -26354.8 -34064.7 93662.9 125335.0 [J kg^-1] 127728.0 [J kg^-1]

H0 -9949.33 -9416.53 176135.0 175322.0 [J kg^-1] 185552.0 [J kg^-1]

Rothalpy -10090.1 -10078.3 -6686.46 -2979.9 [J kg^-1] 171378.0 [J kg^-1]

Entropy -33.8336 -29.5325 -2.0767 14.2871 [J kg^-1

K^-1]

174505.0 [J kg^-1]

Mach (abs) 0.5477 0.6671 0.9797 0.7295

3391.83 [J kg^-1]

Mach (rel) 0.9458 1.0094 0.5181 0.9252

27.4559 [J kg^-1 K^-1]

Cm 181.08 208.178 143.2610 109.4190 [m s^-1] 0.3126

Cu 0.2589 4.3006 361.9730 278.4380 [m s^-1] -0.4913

C 181.089 216.14 392.0440 303.3680 [m s^-1] 246.817 [m s^-1]

Wu -251.266 -247.655 -136.798 -364.9230 [m s^-1] -64.9169 [m s^-1]

W 312.745 326.344 206.688 384.5760 [m s^-1] 357.672 [m s^-1]

Flow Angle (abs)

0.0848 3.8631 71.1707 71.9872 [degree] 175.904 [m s^-1]

Flow Angle (rel)

-52.7474 -48.1407 -14.6369 -29.7745 [degree] 110.857 [m s^-1]

W 312.745 326.344 206.688 384.576 0.6333 -119.656 [m s^-1]

Distortion Parameter

1.0006 1.0921 1.0619 1.0389 0.9724 N/A

Flow Angle: Alpha

0.0848 3.8631 71.1707 71.9872 N/A 67.3076 [degree]

Flow Angle: Beta

-52.7474 -48.1407 -14.6369 -29.7745 N/A 33.5038 [degree]

Note: Diffuser inlet metal angle is 71.9872 degrees at the outlet which is desirable. And, this

makes the impeller suitable with the diffuser

16

2.4.6. Charts

The following charts represent the flow angle, velocity, mach number and entropy

Chart 2.1. Row1 blade loading chart

Chart 2.2. Row1 chart showing circumferentially

averaged flow angle at the LE


averaged flow angle at the TE


averaged relative and absolute Mach number at the TE

17


averaged Cm at the TE


averaged relative Mach number at the LE

Chart 2.7. Chart showing streamwise, area averaged

relative Mach number versus averaged normalized M.

18

2.4.7. Figures

The following figures show blade-to-blade contour and vector views, circumferentially

averaged meridional views, streamwise mass or area averaged quantities from the inlet to

the outlet of the full machine.

Figure 2.6. Stage 1 contours of circumferentially area-

averaged meridional velocity

Figure 2.7. Stage 1 contours of circumferentially area-

averaged relative Mach number

Figure 2.8. Stage 1 contours of relative Mach number at

10% span

Figure 2.9. Stage 1 contours of relative Mach number

at 50% span

19

Figure 2.10. Stage 1 contours of relative Mach

number at 90% span

Figure 2.11. Stage 1 contours of relative total pressure

at 10% span


at 50% span


at 90% span

20

Figure 2.14. Stage 1 contours of circumferentially

area-averaged static pressure

Figure 2.15. Stage 1 velocity vectors at 10% span



21

2.4.8. Streamwise Charts

The following charts show blade loading and spanwise-averaged quantities for each component.

Chart 2.8. Streamwise Plot of Pt and P

Chart 2.9. Streamwise Plot of Tt and T

Chart 2.10. Streamwise Plot of Absolute and

Relative Mach Number

Chart 2.11. Spanwise Plot of Relative Mach Number

at LE

22

Chart 2.12. Spanwise Plot of Relative Mach

Number at TE

Chart 2.13. Spanwise Plot of Absolute Mach

Number at TE

Chart 2.14. Spanwise Plot of Meridional Velocity at

TE

23

2.4.9. Blade Geometry Figures

Figure 2.18. Isometric 3D View of the Blade, Hub

and Shroud

Figure 2.19. Meridional View of the Blade, Hub

and Shroud

Figure 2.20. Mesh elements at %50 span

Figure 2.21. Contour of M rel at 20% Span

24



Figure 2.24. Velocity Vectors at 20% Span


25


Figure 2.27. Vector of Area Averaged Cm on

Meridional Surface

Figure 2.28. Contour of P at Blade LE

Figure 2.29. Contour of M rel at Blade LE

26

Figure 2.30. Contour of P at Blade TE

Figure 2.31. Contour of M rel at Blade TE

Figure 2.32. Velocity Streamlines at Blade TE

27

2.5. Numerical Results (Off-Design point)

This section gives information about performance results for the off-design point

(mass flow rate, rotational speed, total pressure ratio, isentropic efficiency etc.).

2.5.1. Pressure Ratio, Isentropic Efficiency, Mass Flow Rate

This report contains results for off-design point and the requirements were given in table below.

Table 2.11. Off-Design Point Requirements [2]

The Table 2.13 summarizes the performance results and it can be seen that mass flow

rate, total pressure ratio and isentropic efficiency were obtained as required.

Table 2.8. Performance Results

Rotational Speed 7330.3800 [radian s^-1]

Tip Diameter 0.0992 [m]

Tip Speed 363.6860 [m s^-1]

Mass Flow Rate 0.4318 [kg s^-1]

Power 41664.2000 [W]

Inlet Flow Coefficient 0.0983

Total Pressure Ratio 2.3858

Total Temperature Ratio 1.3314

Total-to-Total Isentropic Efficiency % 89.0792

Total-to-Total Polytropic Efficiency % 90.3448

Polytropic Head 87167.1000 [J kg^-1]

Polytropic Head Coefficient 0.6590




Diffuser Cp 0.2573

28

2.5.2. Surge Margin

Requirement: Surge margin value of the compressor shall be either equal to or greater

than 12.

Pressure ratio vs mass flow rate graph is drawn according to analyzes results. Different mass

flow rate values were defined as the outlet boundary condition and the results were listed

below. When mass flow rate decreases, pressure increases at some point (surge poiny). After

that, it begins to decrease while mass flow rate decreases.

Table 2.9. Design Points Analyzes Results

Name P1 - Max

Iterations

P2 - Base

Duty

Speed

P3 - Mass

Flow

P10 - Isentropic

Efficiency (t-t)

P11 - P0

Ratio (t-t)

P12 - T0 Ratio

(t-t)

Units rev

min^-1

kg s^-1

DP 1 400 96000 0,55 91,177 2,23425 1,31061

DP 2 400 96000 0,5 90,7182 2,30175 1,31786

DP 3 400 96000 0,45 89,3039 2,36145 1,32849

DP 0

(Current)

400 96000 0,432 89,1147 2,38667 1,33192

DP 4 400 96000 0,4 87,3559 2,41922 1,3413

DP 5 400 96000 0,35 84,2302 2,45672 1,35935

DP 6 400 96000 0,3 81,2147 2,46477 1,37322

DP 7 400 96000 0,25 79,5203 2,41305 1,38321

29

Figure 2.33. Location of the estimated Surge Margin

Table 2.10. Surge Point Analaysis Results for Off-Design Point

Surge Point Analysis Results

Mass Flow Rate 0,35 kg/s

Pressure Ratio 2,4567

Isentropic Efficiency %84,23

Base Speed 70000 rpm

Percent Speed %100

Surge margin value should be found by means of the below-given formula.

PRt-t/stall: Total pressure ratio at Stall/Surge point

PRt-t/tas.: Total pressure ratio at Design point

ṁt-t/stall: Air flow rate (kg/s) at Stall/Surge point

ṁt-t/tas.: Air flow rate (kg/s) at Design point

PRt-t/stall = 2,4567 ṁt-t/stall = 0,35 kg/s

PRt-t/tas = 2,3858 ṁt-t/tas = 0,432

Surge margin calculation for the current study:

( 2,4567

2,3858∗

0,432

0,35− 1) ∗ 100 = 𝟐𝟕, 𝟎𝟗

30

2.5.3. Required parameters versus obtained parameters

Table 2.11. Comparison of the Required and CFD Results for the Design Point

Required

CFD

Results Unit Is the Condition Met? Error

Mass Flow Rate 0,431 ≤ 𝑚 ≤ 0,491 0,432 𝑘𝑔/𝑠 YES

Isentropic

Efficiency % ≥ 85 89,08 - YES

Total Pressure

Ratio 2,49 ≤ 𝜋 ≤ 2,69 2,39 - NO % 4,01

Surge Margin ≥ 12 27,09 - YES

2.5.4. Detailed Summary

The table below gives a summary of the mass or area averaged solution variables and derived

quantities computed at the inlet, leading edge (LE Cut), trailing edge (TE Cut) and outlet

locations for the off-design point . The flow angles are measured with respect to the axial

direction.

31

Table 2.12. Summary Data Table for Off-Design Point

Quantity Inlet LE Cut TE Cut Outlet Units TE-LE Units

Density 1.1726 1.1576 1.7222 1.8546 [kg m^-3] N/A [kg m^-3]

P 95819.3 94557.0 171318.0 193129.0 [Pa] 76761.4 [Pa]

P0 (abs) 102096.0 103056.0 256079.0 243586.0 [Pa] 153023.0 [Pa]

P0 (rel) 102003.0 101229.0 97180.0 94649.5 [Pa] -4048.48 [Pa]

T 284.619 282.476 343.046 358.688 [K] 60.5693 [K]

T0 (abs) 289.831 290.162 386.400 385.89 [K] 96.2376 [K]

T0 (rel) 289.755 289.755 292.035 293.809 [K] 2.2797 [K]

H -13590.8 -15742.7 45093.1 60804.0 [J kg^-1] 60835.8 [J kg^-1]

H0 -8356.08 -8023.23 88637.9 88126.5 [J kg^-1] 96661.1 [J kg^-1]

Rothalpy -8432.06 -8432.09 -6142.34 -4360.58 [J kg^-1] 89205.9 [J kg^-1]

Entropy -30.6103 -29.5965 -10.8368 -1.7505 [J kg^-1

K^-1]

90157.2 [J kg^-1]

Mach (abs) 0.3024 0.3495 0.7694 0.5793

2289.75 [J kg^-1]

Mach (rel) 0.6253 0.6237 0.4348 0.7617

18.7597 [J kg^-1

K^-1]

Cm 102.271 109.58 116.4 91.8276 [m s^-1] 0.42

Cu 0.1955 7.921 259.435 196.786 [m s^-1] -0.1888

C 102.281 117.595 287.003 221.131 [m s^-1] 179.971 [m s^-1]

Wu -183.208 -175.797 -104.252 -272.332 [m s^-1] 6.8204 [m s^-1]

W 211.517 209.793 161.883 290.76 [m s^-1] 251.514 [m s^-1]

Flow Angle

(abs)

0.1136 8.8607 67.7849 68.2487 [degree] 169.408 [m s^-1]

Flow Angle

(rel)

-59.2249 -51.5514 -26.325 -36.5414 [degree] 71.5448 [m s^-1]

W 211.517 209.793 161.883 290.76 0.7716 -47.9105 [m s^-1]

Distortion

Parameter

1.0008 1.1359 1.0559 1.042 0.9296 N/A

Flow Angle:

Alpha

0.1136 8.8607 67.7849 68.2487 N/A 58.9241 [degree]

Flow Angle:

Beta

-59.2249 -51.5514 -26.325 -36.5414 N/A 25.2264 [degree]

Note: Diffuser inlet metal angle is 68.2487 degrees at the outlet which is desirable. And, this

makes the impeller suitable with the diffuser

32

2.5.5. Mesh Independency

Different mesh element numbers were tried to ensure that results do not depend on the

mesh element number. There is no significant difference between them and the error does not

exceed 0.1 %.

Table 2.13. Mesh Independecy Data

Number of Mesh Isentropic Efficiency (t-t) Pressure Ratio

100000 88,471 2,39257

200000 88,8326 2,39462

300000 88,7877 2,39467

400000 88,6789 2,392

500000 88,8093 2,3912

600000 88,7602 2,38967

700000 88,7557 2,38919

800000 88,6993 2,38826

900000 88,701 2,38774

1000000 88,7814 2,3877

1100000 88,7454 2,38641

1200000 88,7464 2,38682

1300000 88,7186 2,38604

1400000 88,701 2,38532

1500000 88,6474 2,38458

Figure 2.34. Mesh Independecy Study Pressure Ratio vs. Number of Mesh

33

3. STRUCTURAL

In this section, the method that was used to perform the structural analysis of the impeller is

explained and results of the analyzes are given.

3.1. Material Properties

Aluminum 2124 Alloy was used as a material of the impeller and its properties were listed

in Table 6.3.

Table 3.1 Properties of Aluminum 2124 Alloy

Aluminum 2124 Alloy Value Units

Elastic Modulus 73500 N/𝑚𝑚2

Poisson's Ratio 0.33 N/A

Shear Modulus 27000 N/𝑚𝑚2

Mass Density 2780 𝐤𝐠/𝒎𝟑

Ultimate Tensile Strength 508 N/𝑚𝑚2

Yield Strength 441 𝐍/𝒎𝒎𝟐

Thermal Expansion Coefficient 2.3e-005 1/K

Thermal Conductivity 151 W/(m · K)

Specific Heat 882 J/(kg · K)

Melting Point 510 °C

For thermal conductivity values, the default values in Ansys Engineering Data for Aluminum

Alloy were used in the analyzes, and these values are listed in table below.

Table 3.2 Thermal Conductivity Values

Thermal Conductivity W m^-1 C^-1 Temperature C

114, -100,

144, 0,

165, 100,

175, 200,

34

3.2. Structural Analysis

To perform the structural analysis of the impeller, Ansys Static Structural module was used,

and Ansys Workbench for the analysis is shown in figure below.

Figure 3.1 Ansys Workbench For Structural Analysis

Ansys Steady-State Thermal module was used to transfer the body temperature to the

structural analysis.

Material properties were set in ‘Engineering Data’ using the values which are listed in Table

6.3. The created geometry was then imported, and the boundary conditions were set in

‘Model’.

3.2.1. Meshing

Initially, meshing process was performed and the details about the mesh properties are given

in Table 3.3. The analyzes were performed using various mesh numbers from 50,000 to

1,300,000 and it was observed that there is no a constant relation between the mesh number

and the results. We obtained reasonable results for the mesh numbers between 200,000

400,000. The results of the structural analysis in this report were obtained for 358,371 mesh

number.

35

Table 3.3 Mesh Properties

Object Name Mesh

State Solved

Display

Display Style Body Color

Defaults

Physics Preference Mechanical

Relevance 0

Element Order Program Controlled

Sizing

Size Function Uniform

Relevance Center Fine

Transition Slow

Min Size Default (2,2208e-005 m)

Max Face Size 1,3e-003 m

Max Tet Size Default (4,4416e-003 m)

Growth Rate Default (1,20 )

Automatic Mesh Based Defeaturing On

Defeature Size Default (1,1104e-005 m)

Minimum Edge Length 2,3649e-006 m

Quality

Check Mesh Quality Yes, Errors

Error Limits Standard Mechanical

Target Quality Default (0.050000)

Smoothing Medium

Mesh Metric None

Inflation

Use Automatic Inflation Program Controlled

Inflation Option Smooth Transition

Transition Ratio 0,272

Maximum Layers 8

Growth Rate 1,2

Inflation Algorithm Pre

View Advanced Options No

Advanced

Number of CPUs for Parallel Part Meshing Program Controlled

Straight Sided Elements No

Number of Retries 0

Rigid Body Behavior Dimensionally Reduced

Mesh Morphing Disabled

Triangle Surface Mesher Program Controlled

Topology Checking No

Pinch Tolerance Default (1,9987e-005 m)

Generate Pinch on Refresh No

Statistics

Nodes 732322

Elements 358371

36

A general mesh view is as shown below.

Figure 3.2 Mesh View

3.2.2. Steady-State Thermal

It is assumed that there are two convection surfaces on the impeller. The first convection

surface (convection fluid surface) is the surface that air flows from the inlet to the outlet, as

shown in Figure 3.3 The ambient air temperature for this convection surface was defined as a

various temperature load on the surface, as listed in Table 3.4. The temperature values were

taken from CFD results, and were set along the Z direction. A convection coefficient of

500 𝑊/𝑚2°𝐶 was determined using a rough calculation.

Table 3.4 Ambient Temperature Values For Convection Fluid Surface

Z [m] Ambient Temperature [°C]

-4,801e-002 15,

-3,6e-002 20,

-2,16e-002 67,

-1,1e-002 167,

-5,76e-003 200,

0,

37

Figure 3.3 Convection On Fluid Surface

Second convection surface is the back face of the impeller, as shown in Figure 3.4. The reason

for convection on the back face is a probable leakage flow through the gap between the

impeller end and the diffuser. Since there is a reduction in air velocity, air density and flow

area, a lower convection coefficient (300 𝑊/𝑚2°𝐶) was defined on the back face.

Figure 3.4 Convection On Back-Face

38

However, the air temperature that flows over the back face was assumed to be 110 °C which

is lower than the outlet temperature of the impeller due to the losses between the impeller and

diffuser.

Additionally, two temperature conditions were set on the impeller, as shown in figures below.

The values of these temperatures were assumed to be 30 °C.

Figure 3.5 Temperature Condition On Front Surface

Figure 3.6 Temperature Condition On Back-Face

39

3.2.3. Static Structural

After setting all conditions in Steady-State Thermal module, the analysis was performed and

the body temperature was directly imported to the structural analysis.

There are four conditions that need to be set prior to performing the structural analysis. These

are ‘‘temperature load, pressure load, rotational velocity, and fixed support’’.

Temperature load was imported from Steady-State module as shown in figure below.

Figure 3.7 Imported Body Temperature

Pressure load was defined on the flow surface and different pressure values through the

impeller were set along the Z direction using the values from CFD analysis. The obtained

pressure load is as shown in figure below.

40

Figure 3.8 Variable Pressure Load

Rotational velocity was set to be 96000 RPM as shown in Figure 3.9.

Figure 3.9 Rotational Velocity Condition

41

To get better results in structural analysis, a shaft geometry should also be added to the

impeller, however, we performed the analyzes using the impeller without a shaft. Since there

is no shaft, the surface between the impeller body and the shaft body was set as fixed support,

as shown in figure below.

Figure 3.10 Fixed Support Condition

3.2.4. Results

Steady-State Thermal and Static Structural analyzes were performed for mesh number of

358,371 and results are given in this section.

Equivalent Stress

The equivalent stress distribution on the impeller is shown in Figure 3.11, 12 and 13.

42

Figure 3.11 Equivalent Stress Distribution at 96000 RPM (isometric view)

Figure 3.12 Equivalent Stress Distribution at 96000 RPM (back view)

43

Figure 3.13 Equivalent Stress Distribution at 96000 RPM (section view)

The maximum stresses occur on the root of the blades, that’s why a high value of fillet was

set between root of the blades and the impeller disk.

The requirement for the equivalent stress is that the stress values must be lower than 0.2%

yield strength of the material. The important point here is about the yield strength value of the

material. The materials have various yield strength values with respect to temperature,

therefore, operating surface temperature must be considered to determine the yield strength

value of the material.

44

Yield strength of the material and maximum stress value are listed in table below.

Table 3.5 Yield Strenth Requirement and Analysis Result

Tensile Yield Strength (Mpa)

(at maximum surface temperature,

130°C)

Maximum Equivalent Stress

380 Mpa 349 Mpa

Since the equivalent stress results show a maximum stress value of 4646546 which is

relatively lower than 0.2% yield strength of the material, the impeller can withstand the

structural loads (pressure, temperature, centrifugal etc.) during its duty.

Total Deformation

Total deformation distribution on the impeller is shown in figures below.

Figure 3.14 Total Deformation Distribution at 96000 RPM (isometric view)

45

Figure 3.15 Total Deformation Distribution at 96000 RPM (back view)

Fatigue

The requirement for fatigue is that the impeller must withstand more than 1000 cycle against

the local stress values.

We have conducted a deep study to find information and calculation methods for the fatigue

behavior of Al 2124 Alloy. However, we could not obtain useful information due to the lack

of time.

According to the structural analysis results, we may have some ideas about the fatigue life og

the impeller. After the conducted study for fatigue behavior of the material, it was observed

that the maximum stress value must be lower than yield strength of the material for at least

1000 cycles. As can be seen in our stress results, the maximum stress is considerably lower

than the yield strength of the material.

As a result, one can easily see that the impeller can withstand the structural loads for at least

1000 cycles during its duty.

46

Burst

Another mechanical requirement is that the impeller disk should not burst up to +20% of

operating rotational velocity. Therefore, equivalent stress results should again be examined

by performing a new structural analysis. However, it is not the yield strength that needs to be

considered, it is the ‘Ultimate Tensile Strength’. If the maximum equivalent stress is more

than the ultimate tensile strength of the material, then there may be burst on the impeller disk.

For this requirement, the rotational velocity was set to be 115200 which is +20% of operating

rotational velocity in structural analysis, and stress results are as shown in figures below.

Figure 3.16 Equivalent Stress Distribution at 115200 RPM (isometric view)

47



48

The Ultimate Tensile Strength of the material is about 485 Mpa at 130 °C which is near the

surface temperature of the impeller. The maximum equivalent stress is little higher than the

ultimate strength of the material. It is possible for the impeller to be burst at 115200 RPM.

An additional analysis was also performed by setting a rotational velocity of 110000 RPM,

and results are given in following figures.

Figure 3 19 Equivalent Stress Distribution at 110000 RPM (isometric view)

49



50

110000 RPM can be seen as the safe rotational velocity for this impeller in specified

environmental conditions and structural loads, without any burst phenomenon.

4. VIBRATION

Vibration phenomena happens in rotating machines due to imbalances on the structure of the

machine. This phenomenon is significantly important in turbomachinery and must be taken

into account for the structural design.

Vibration analysis were also performed in Ansys using ‘Modal Analysis’ module.

4.1. Modal Analysis

To perform the vibration analysis of the impeller, ‘Modal Analysis’ module is connected to

‘Static Structural’, as shown in figure below. When connected, a modal tree is automatically

added to the analysis tree in ‘Model’.

Figure 3.22 Ansys Workbench For Modal Analysis

In model tree, rotational velocity should be defined. In this project, the natural frequency

values will be examined for two rotational velocities, so that two rotational velocity values

should be defined as a tabular data.

In ‘Analysis Settings’, we need to define number of modes, and also set ‘Damped’, ‘Corriolis

Effect’ and ‘Campbell Diagram’ on to generate a Campbell Diagram.

Campbell Diagram is a kind of graph that shows natural frequency versus rotational velocity

and an example is shown in Figure…….

51

Figure 3.23 An Example of Campbell Diagram

The straight lines are natural frequency lines and the sloped lines are called as Engine Order

(EO) lines. These lines are used to make comments on the graph, and also to determine the

critical speeds of a rotating system. When a natural frequency line intersects with an Engine

Order line, resonance occurs.

The EO line can be defined in Campbell Diagram settings, by changing ‘Ratio’. For 2EO,

‘Ratio’ must be 2.

4.2. Requirements

There are two requirements for vibration analysis of the impeller.

The first one is that natural frequencies of the blisk (disk+blades) should not intersect with

2EO, in the range of ±20% of maximum rotational velocity of the engine while the engine

is operating.

The second one is that natural frequencies of the blades should not intersect with 2EO, in the

range of ±10% of maximum rotational velocity of the engine while the engine is operating.

52

4.3. Analysis for Blisk

Modal analysis were performed for blisk in the range of 76800 RPM to 115200 RPM and the

Campbell Diagram is shown in Figure 3.24. The natural frequency values were also listed in

Table 3.6.

Figure 3.24 Campbell Diagram For Blisk Structure

53

Table 3.6 Natural Frequency Values For Blisk Structure

Mode Whirl Direction Mode Stability Critical Speed 76800 rpm 1,152e+005 rpm

1, FW STABLE 0, rpm 5612, Hz 5407,1 Hz

2, FW STABLE 0, rpm 5661,4 Hz 5439,4 Hz







9, BW STABLE 0, rpm 8263,7 Hz 7858,1 Hz


11, BW STABLE 0, rpm 8335,2 Hz 7957, Hz

12, BW STABLE 0, rpm 8368, Hz 7991,4 Hz




16, BW STABLE 0, rpm 11125 Hz 10744 Hz











27, FW STABLE 0, rpm 14777 Hz 15240 Hz



















54

4.4 Analysis For Blades

The modal analysis of the blades were performed separately from the disk structure. The

geometry of solved blade model is shown in figure below. The surfaces that are in contact

with the disk structure were set as ‘fixed support’, as shown below.

Figure 3.25 Geometry of Blades For Modal Analysis

Figure 3.26 Fixed Support Surfaces

55

Modal analysis were performed for blades in the range of 86400 RPM to 105600 RPM and

the Campbell Diagram is shown in Figure 3.27. The natural frequency values were also listed

in Table 3.7.

Figure 3.27 Campbell Diagram For Blade Structure

56

Table 3.7 Natural Frequency Values For Blade Structure

Mode Whirl Direction Mode Stability Critical Speed 86400 rpm 1,056e+005 rpm
























24, FW STABLE 0, rpm 9671,6 Hz 9564, Hz






















57

5. Balance (Dengeleme)

The figures below show where the balance locations are. The surfaces were chosen where

the fluid and solid does not intersect. Because, it may affect the performance when the fluid-

solid surfaces were machined. It is recommended to choose the back-face of the impeller as

the balance location to prevent occurring of unwanted flow structures due to the

modifications on the surface for balance.

Figure 5.1 General view of the balance locations

58

IMPELLER DATA

Impeller Mass : 247.01 gr

Service Speed: 96000 rpm

Table 5.1 Balance quality grade

Machinery types: General examples

Balance

quality grade

G

Magnitude

eper. Ω

mm/s

• Compressors

• Computer drives

• Electric motors and generators (of at least 80 mm shaft

height), of maximum rated speeds above 950 r/min

• Gas turbines and steam turbines

• Machine-tool drives

• Textile machines

G 2,5 2,5

Balance quality grade was choses as equals to 2.5 from the table which is given in ISO 1940.

Calculated: Angular velocity of service speed, from

Ω = π∗ n

30 =

π ∗96000

30= 10053.096 𝑟𝑎𝑑/𝑠

Uper =(eper* Ω). 𝑚

Ω =

2.5 ×247.01 𝑔𝑟

10053.096 = 0.061426 gr.mm

where

Uper is the numerical value of the permissible residual unbalance, expressed

in gram milimetres (g.mm)

(eper. Ω) is the numerical value of the selected balance quality grade, expressed in

milimetres per second (mm/s)

m is the numerical value of rotor mass, expressed in kilograms (kg)

Ω is the numerical value of the angular velocity of the maximum service

speed, expressed in radians per second (rad/s)

Uper=eper * m → 0.061426 gr.mm = eper * 247.01 gr

59

eper = 0.2486 gr.mm/kg

CHECK

Figure 5.2 Permissible residual specific unbalance based on balance quality grade G and

service speed n

Note: Figures and tables of this section were taken from ISO 1940 document.

60

6. Assembly (Montaj)

Bu bölüm yaptığımız tolerans ölçülerini daha iyi anlatabilmek için türkçe

hazırlanmıştır. Öncelikle toleransların hesaplanmasında kullanılan formüller yerine

Uluslararası Standart Organizasyonu tarafından belirlenen tabloların kullanılması tercih

edilmiştir. Ayrıca, hesaplama yapılmaya çalışılmış olup şaft ile kompresör arasındaki

sürtünme katsayısının bilinmemesinden dolayı çalışmalar ilerleyememiştir.

Figure 6.1. ISO ALISTIRMA TABLOSU

Bizden istenen kompresörün çok yüksek açısal hızlarda dönmesinden dolayı geçmenin pres

ile geçme olması kararlaştırılmıştır. Sadece açısal hızın çok yüksek olmasının yanında yüksek

hızla dönen turbo makineler üzerine literatür çalışması yapılmıştır. Yapılan çalışma da

geometrik özellikleri ve yüksek açısal hızlı deneysel çalışmalar incelenmiştir. Ayrıca,

hocalarımızdan aldığımız tavsiye üzerine pres ile sıkı geçmede(R7/h6) karar kılınmıştır.

61

7. Producubility

Definition: Ease of manufacturing an item (or a group of items) in large enough

quantities. It depends on the characteristics and design features of the item that enable its

economical fabrication, assembly, and inspection or testing by using existing or available

technology. [3]

When designing an impeller, ANSYS software allows to change the angle and thicknes

at different span locations. In this project, five span locations (%0, 25, 50, 75, 100) were

available to change for design, however, only two span locations, %0 and %100, were used,

and blade angle and thickness values at other span locations were calculated by the software

according to the first and last span. This approach has some advantageous and

disadvantageous on the performance and producibility of the radial impeller. Increasing the

efficiency and changing the pressure ratio may be difficult when the angles, thickness and the

other parameters are changed at Span 0 and Span 1. That is, one may not have high opportunity

to reach the desired values. Even if it seems to be bad idea to change the angles and thickness

just at span locations %0 and %100, producibility of this product will be much more easier.

The figures (below) shows the span where the Angle and Thickness curve can be

changed. In our design, we prefer to have two span location to change these curves. Even if it

took so much time to reach the desired efficiency and pressure ratio, it is easy to manufacture.

Figure 7.1. Angle and Thickness Layer Control

The figures (below) show the difficulty of the radial impeller when the angles and thickness

can be changed at Span 0, 0.25, 0.5, 0.75, 1.

62

Figure 7.2. Blade geometry

Note : Angles were exaggerated to show the difficulty of the radial impeller

manufacturing when the angles and thickness can be changed at Span 0, 0.25, 0.5,

0.75, 1.

63

8. CAD MODEL AND GEOMETRY

This section covers the used programs and their functions, geometric properties of the CAD

model which characterize the impeller geometry and mass properties of the impeller.

8.1. Modeling of Impeller

Vista CCD

ANSYS Vista CCD software program was used to create the model of the impeller. The Vista

software includes 1D design and off-design performance programs for many turbomachines

such as axial turbines, radial turbines, axial compressors, axial fans, centrifugal compressors,

and centrifugal pumps.

Vista CCD is a program for the preliminary design of centrifugal compressors. It can be used

to create a 1D design. The resulting geometry can be transferred to BladeGen or BladeEditor.

Vista CCD is also integrated into ANSYS Workbench, therefore it may be used to generate

an optimized 1D compressor design before the 3D geometry model and CFD analysis.

BladeGen

Input of the Vista CCD (hub and tip diameter, backsweep, rake angle etc.) is transferred to the

BladeGen to create the 3D CAD model. Blade thickness, blade angles, backsweep etc. can

be arranged by using the BladeGen. We defined the compressor tip profile points which are

given to us and all the geometric restrictions applied to the CAD model by using BladeGen.

After all the arrangements, geometry is exported in *.stp format and rearranged in

SolidWorks.

Blade Number

Blade number is important parameter which affects the weight, efficiency, pressure ratio etc.

7 blades were determined to use to minimize the mass of the impeller. The number of impeller

blades are arranged not to be multiples of 6 and 8. Also, 7 bladed design has advantageous

about the producibility when compared to others.

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Hub Diameter, Shroud Diameter, Tip Clearance

Tip clearance and shroud diameter are given to us as 0.25 mm and 70.6 mm, respectively. It

can be easily seen in the Figure 6.1 [2] that shroud diameter equals to 70.6. Point 10 has 35.30

vertical distance from the origin. Diameter of the shroud is the 2×35.30 = 70.6 mm. Hub

diameter value is determined with the help of written code and Ansys software program. We

decided to assign hub diameter equals to 20 mm.

Figure 8.1 Compressor Tip Profile Sizes [2]

Backsweep Angle

Back-sweep angle is determined using MATLAB code. Back-sweep angle range is defined

between 6° and 45°. The best option which provides the conditions (Pressure ratio, isentropic

efficiency etc.) is the 30° back-sweep. After the selection of the back-sweep angle, some

analyzes were made to compare the analytical and CFD results. 2% deflection was observed

which is acceptable between the analytic and CFD results. In short, 30° back-sweep Angle

(𝜷𝟐𝒃) is the best option for our geometry.

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Rake Angle

Figure 8.2 Rake angle (Vista CCD Help)

Rake angle =λ the angle between the trailing edge and the back face of the disc, typically

between zero and 45°, often around 30°. Also, rake angle is important parameter for the

stresses and structural design.

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8.2. Geometric Properties

Geometric properties which characterize the impeller were listed in Table 6.1. These

parameters can be used as an input in Vista CCD software.

Table 8.1 Impeller Geometric Properties (Vista CCD)

Parameters Value Units

Main vanes 7 -

Inter vanes 7 -

Backsweep 30 deg

Rake angle 30 deg

Hub Diameter 20 mm

Vane normal thickness (hub) 1,8 mm

Shroud Diameter 70,6 mm

Vane normal thickness (shroud) 0,9 mm

Tip Clearence 0,25 mm

Vane roughness Machined Finish

Isometric, left and front view of the impeller are as shown in Figure 6.3.

(a) (b) (c)

Figure 8.3 Isometric (a), left (b) and front (c) views of the impeller.

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8.3. Technical Drawing

Technical drawing is prepared in SolidWorks and exported to pdf format. Front view, left

view and AA section are shown in the technical drawing. Also, necessary dimensions,

tolerances and surface roughness are illustrated in the drawing. Facilitating the production of

the impeller is an important factor during tolerance-adding process. High rotational speed and

small dimensions are also considered in the tolerance-adding process. Concentricity is an

important factor for rotating parts due to vibrations. Tolerance of parallelism between the back

and front faces is added for compatibility of the impeller itself and casing. One of the most

important tolerance is between the hole and shaft. Press fitting method was chosen as an option

for the assembly of the impeller and shaft. Considering the high rotational speed, h6/R5

tolerance was given. Surface roughness is a key factor for the losses and determined as 1.6

micron for the regions shown in the drawing, then the other regions should be 0.8 micron, as

shown in the top-right of the technical drawing.

8.4. Mass of the impeller

Mass of the impeller is an important subject of the impeller design. After the creation of the

CAD model, we add Aluminum 2124 alloy as a material of the impeller. Mass of the impeller

is affected by the blade numbers, blade thickness, back-sweep etc. Much effort exerted to

reduce the mass and mass of the impeller equals to 250.96 g. Mass, volume and surface area

of the impeller were listed in Table 6.2.

Table 8.2 Impeller Properties

Parameters Value Units

Mass of the Impeller 247.02 grams g

Volume 88855.85 mm3

Surface Area 44272.95 mm2

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9. CONCLUSION

• There are some basic parameters which affect the performance of the impeller and the

most important ones are blade angle, blade thickness, mass of the impeller and blade

number.

• In the design process, blade angles were changed to have higher efficiency and it is

easy to get the conclusion that blade angle is one of the most important parameters that

affects the pressure ratio and impeller efficiency.

• Blade number is also important for the efficiency and pressure ratio and one should

notice that increasing the blade number will also increase the weight. This can cause

efficiency drop and problem about the producibility.

• In this study, splitter blades were used to achive high pressure ratios and avoid

chocking of the flow at the inlet. This method is used by the compressor designers

mostly due to the same reason.

• Efficiency may decrease with low blade number primarily due to low momentum

exchange. Also, blade thickness should be arranged properly to withstand the pressure

in the radial compressor.

• Mass of the impeller is another key parameter because when mass of the impeller is

increased, the energy required to rotate compressor will also increase.

• Even if a high-efficient radial impeller is designed, some problems may be

encountered while manufacturing process due to the limitations depending on the

manufacturing method.

• Every part or machine must have tolerances because there are no certain measures in

the real world. One should attain these tolerances with properly not to have penetration

of the parts.

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REFERENCES

[1] TEKNOFEST, Mini Jet Radial Compressor Design, Competition Specifications

[2] TS ISO 1940, Mechanical Vibration, Balance quality requirements for rotors in a

constant (rigid) state, part 1: Specification and verification of balance tolerances

[3] http://www.businessdictionary.com/definition/producibility.html

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APPENDIX A : TECHNICAL DRAWING OF THE CAD MODEL

Documents

AVIATION, AEROSPACE AND TECHNOLOGY FESTIVAL ...Figure 3.16 Equivalent Stress Distribution at 115200 RPM (isometric view) ..... 46 Figure 3.17 Equivalent Stress Distribution at 115200