Table Of ContentAXIAL FLOW FANS AND COMPRESSORS
To my grandson, Neil, without whose interest this book
might never have been completed
Cranfield Series on Turbomachinery Technology
Series Editor: Robin L. Elder
Axial Flow Fans and
Compressors
Aerodynamic Design and Performance
a. b. McKenzie
Visiting Professor
School of Mechanical Engineering
Cranfield University
Bedford
Ashgate
Aldershot • Brookfield USA • Singapore • Sydney
O A. B. McKenzie 1997
All rights reserved. No pan of this publication may be reproduced, stored in a retrieval
system, or transmitted in any form or by any means, electronic, mechanical, photocopying,
recording or otherwise without the prior permission of the publisher.
Published by
Ashgate Publishing Limited
Gower House
Croft Road
Aldershot
Hants GU11 3HR
England
Ashgate Publishing Company
Old Post Road
Brookfield
Vermont 05036
USA
British Library Cataloguing in Publication Data
McKenzie, A. B.
Axial flow fans and compressors : aerodynamic design and
performance. - (Cranfield series in turbomachinery)
1. Axial flow compressors 2. Axial flow compressors - Design
3. Aerodynamics
I. Title
621.5' 1
Library of Congress Cataloging-in-Publkation Data
McKenzie, A. B., 1926-
Axial flow fans and compressors : aerodynamic design and
performance / A. B. McKenzie,
p. cm.
Includes bibliographical references.
ISBN 0-291-39850-2
1. Fans (Machinery)*-Aerodynamics. 2. Axial flow compressors-
- Aerodynamics. I. Title
TJ960.M35 1997 97-1249
621.6’ l-dc21 CIP
ISBN 0 29139 850 2
Printed in Great Britain by The Ipswich Book Company, Suffolk
Contents
Preface xi
1 The axial fan
Introduction 1
The domestic ventilator 2
Work done 3
The diffusing blade passage 4
Mass flow variation 7
The fan characteristic 9
2 Reaction
Introduction 12
Definition 13
Choice of reaction 15
Variation of reaction with radius 16
3 The work and flow coefficient diagram
Introduction 17
Additions to the diagram 18
Reactions other than 50% 22
The IGV/rotor fan 24
The rotor/stator fan 24
4 Blade loading parameters
Introduction 27
Cascade data 27
Total pressure losses 29
Deviation 29
Axial velocity ratio 30
Compressor data 30
Blade geometry selection 32
vi Axial flow fans and compressors
5 Blade geometry
Introduction 35
The C series of aerofoils 35
American practice 36
Cascade geometry 36
The double circular arc blade 37
Modem trends 38
6 Aspect ratio
Introduction 41
Surge margin improvement 41
Other benefits 42
Technical considerations 43
Equivalent cone angle 45
End wall loss parameter 45
Design criteria 47
7 Relative motion effects
Introduction 49
Blade design with secondary losses 50
Wakes in relative motion 52
Work and flow coefficient effects 53
Radial flow shift through the rotor 54
8 Vortex flow
Introduction 56
Free vortex designs 56
Constant reaction 57
Arbitrary vortex 60
Simple equilibrium 60
Examples of simple equilibrium 61
Constant ‘reaction* design 63
Throughflow computations 65
9 Mach number effects
Introduction 66
High subsonic Mach number • 66
Passage throat width 67
Supersonic Mach number 69
Blade forms for supersonic operation 70
Passage shock waves 70
S/C requirement 71
Laser anemometry 72
Effect of Mach number on overall pressure ratio 73
Contents
10 Reynolds number effects
Introduction
Performance variation
WasselTs correlation
Surface finish effects
11 Compressible flow relationships
Introduction
Notation
Fundamental relationships
Applications
12 The stage characteristic
Introduction
The work coefficient characteristic
The efficiency characteristic
The pressure rise coefficient
Experimental stage characteristics
13 The repeating stage concept
Introduction
The linear repeating stage
Stage of unity work coefficient
14 Spanwise matching of high diameter ratio stages
Introduction
Variable axial profile
Variable work done design
An alternative approach
15 Spanwise matching of low diameter ratio stages
Introduction
Example
Increased diameter ratio
Conclusions from the approximate method
Alternative methods
16 Stall
Introduction
Criteria for progressive or abrupt stall
Surge initiation
Rotating stall
Hysteresis
viii Axial flow fans and compressors
Vibration 119
Passive stall control 120
17 Surge
Introduction 124
An alternative criterion for surge 126
More complex approaches 129
Surge margin 129
18 Performance presentation
Introduction 132
Performance graphs 133
Isentropic and polytropic efficiency 136
Polytropic efficiency 138
Efficiency assessment 140
Efficiency with interstage bleed flows 142
19 Stage matching and surge control
Introduction 144
The stage matching problem 144
Bleed off-take 147
Variable stagger stator blades 149
Industrial axial compressors 150
Twin spool gas turbines 151
Off-design operation of twin spool gas turbines 153
Active surge control 156
20 Inlet flow maldistribution
Introduction 157
Compressors in parallel 158
Distortion parameter 161
Inlet Temperature distortion 162
21 Compressor rig testing
Introduction 164
Power requirements 164
Facility layout 168
Test procedure 171
22 Stage performance prediction
Introduction 174
A preferred method 174
Other methods 179
Off design efficiency 180
Contents ix
23 Overall performance prediction
Introduction 181
Stage stacking 181
Overall performance correlation 183
High speed corrections 188
Test comparison with prediction 190
24 Performance with altered gas properties
Introduction 191
The significance of density ratio 192
Gases other than air 193
Compression of helium 194
Viscosity and Reynolds number 195
25 Design for a domestic ventilator
Specification 196
Overall parameters 196
Blade speed and dimensions 197
Blade selection 198
Half speed operation 200
26 Design for an industrial fan
Specification 201
Preliminary considerations 201
Choice of diameter ratio 202
Rotor blade geometry 203
The outlet stator 206
The outlet diffuser 208
27 Design for a transonic wind tunnel fan
Specification 209
Preliminary considerations 209
Selection of vector geometry 210
The rotor blade 212
The stator 216
Annulus dimensions 218
Design speed 220
Fan efficiency 220
Outlet diffuser 223
Power requirement 224
Operation at higher tunnel Mach numbers 224
28 Design for an industrial compressor
Introduction 226
Design specification 226
Axial flow fans and compressors
X
General considerations 227
Design parameter selection 227
Rotor blade geometry 230
Stator blade geometry 234
Annulus diagram 236
Variation of stage numbers 237
Additional front stages 238
Scaled versions 240
Volume flow 240
29 Outline design for a jet engine compressor
Introduction 241
Specification 241
Overall parameters 242
First stage 243
Last stage 245
Blading 247
30 HP compressor mid-stage
Introduction 248
Datum stage 248
Blade end modifications 249
Rotor design 251
Stator blade 253
Design method 255
31 The high bypass fan
Introduction 256
General arrangement 256
Aerodynamic parameters 257
Rotor blade geometry 260
Fan blade integrity 260
Bibliography 262
