Axial Flow Fans and Ducts

456 Pages·1983·43.691 MB·English

by  R Allan Wallis

Axial Flow
Fans and Ducts

AXIAL FLOW
FANS AND DUCTS
R. ALLAN WALLIS
M.E., A.S.T.C., F.I.E. Aust., M.R.Ae.S.
formerly of
Aeronautical Research Laboratories (Melbourne)
and
CSIRO Division of Mechanical Engineering (Melbourne)
A Wiley-Interscience Publication
JOHN WILEY & SONS
New York «+ Chichester + Brisbane ¢* Toronto °* Singapore
Copyright © 1983 by John Wiley & Sons, Inc.
All rights reserved. Published simultaneously in Canada.
Reproduction or translation of any part of this work
beyond that permitted by Section 107 or 10% of the
1976 United States Copyright Act without the permission
of the copyright owner is unlawful. Requests for
permission or further information should be addressed to
the Permissions Department, John Wiley & Sons, Inc.
Library of Congress Cataloging in Publication Data
Wallis, R. Allan
Axial flow fans and ducts.
“A Wiley-Interscience publication."*
Bibliography: p.
Includes index.
1. Fans (Machinery) 2. Air ducts. I. Title.
TJ960.W34 1983 621.61 83-3540
ISBN 0-471-87086-2
Printed in the United States of America
10987654321
Foreword
With the publication of ‘‘Axial Flow Fans and Ducts’”’ Mr. Wallis has
made a significant contribution to axial flow fan design and to the proper
application of axial flow fans. This book, which is a modern replacement for
an earlier book by the author, will be of importance to fan designers, engi-
neers who are applying axial flow fans to air handling systems, and engineers
responsible for the operation of these systems.
The fan designer will find design procedures presented in a logical se-
quence and the background of the design equations carefully developed.
This book will serve as one of the important elements in planning an axial
flow fan design development program. Mr. Wallis is careful to point out the
limitations of the design method and to call attention to the importance of
laboratory testing for new fan designs. However, an understanding and ap-
plication of this design procedure will allow the designer to arrive at a theo-
retical design that will be an optimum starting point for the test program. In
this way, much of the ‘‘cut and try’’ part of the test program can be elimi-
nated and a new design can be developed more efficiently. The results of the
test program can be incorporated into the design procedure and the effect of
changes in the design variables can be evaluated in an orderly and logical
manner.
A knowledge of the design principles of axial flow fans is of importance to
the engineer applying these fans to air moving systems since many of the
shortcomings of faulty air handling systems can be traced to a lack of under-
standing of what makes a fan work efficiently. Mr. Wallis explains the princi-
ples of axial flow fan design in a way that is quite understandable to engi-
neers engaged in the design and operation of air moving systems. An
understanding of these principles is necessary for the engineer to avoid those
duct configurations that will be detrimental to the fan operation. The empha-
sis on energy conservation requires that fans be operated efficiently. Mr.
Wallis does an excellent job of combining fan design principles with duct
design principles so that a unified picture is presented to the application
engineer.
This book will also be of value to engineers charged with the operation of
air moving systems. Many of their operating problems can be more easily
vi FOREWORD
solved if they have an understanding of the principles of fan design, the
principles of duct design, and the interrelationship between the two.
Although Mr. Wallis has based his design procedures on a solid theoreti-
cal basis, his presentation is a very practical one and shows the results of his
own extensive practical engineering experience. He has written this book for
qualified engineers who want to use current, valid engineering design proce-
dures to improve their work.
For those engineers who wish to investigate any particular phase of the
material, there are extensive references cited which will be most helpful.
J. BARRIE GRAHAM
Santa Fe, New Mexico
July 1983
Preface
It is my belief that uncertainty is a major factor inhibiting the problem-
solving capability of many engineers; lack of confidence is usually associated
with an inadequate physical understanding of basic airflow phenomena.
The necessary background for engineers handling problems in these areas
is presented herein. An understanding of the boundary layer and its charac-
teristics provides the key to design progress. Likewise, a familiarity with
aerofoil design theory, particularly the interrelationship between shape
changes and the boundary layer, is important.
The formulation and proof of many of the basic theorems and concepts on
which aerodynamics is based have been omitted as they are adequately dealt
with in the text book literature. In particular, the reader is required to accept
the non-dimensional concept as essential to progress in relation to all design,
analysis, and test exercises.
The standards adopted in this book promote the attainment of proficiency
in respect to all theoretical and practical aspects of fan and duct technology.
This book would not be complete without some mention of computer
programs. The uncomplicated expressions used in ‘‘free vortex flow’’ de-
signs are, in my opinion, more suited to the hand-held calculator. However,
the tedium of repetitative calculations such as those involved in deriving
blade section coordinates, analyzing probable fan performance, or reducing
fan test data will be reduced by computerization.
A unique program cannot be written for fan design since the spanwise
distribution of lift is not a fixed entity. A series of alternative, plausible
assumptions should therefore be made for insertion into the computer pro-
gram at the appropriate juncture. A fully computerized design method must
be programmed to include additional criteria relating to wall stall, blade load
and swirl limitations, blade aspect ratio, and other fan properties.
Mechanical features, strength, materials, noise, and dust and water ero-
sion are matters which require consideration before completing the aerody-
namic design; their interactions with the latter are outlined in the text.
I am particularly indebted to Mount Isa Mines Ltd. for the opportunity to
work closely with their engineers in putting theory into practice on a large
and satisfying scale. Much of the stimulus for the applied research studies
vii
viii PREFACE
undertaken owes its origin to equipment problems encountered by the com-
pany. Research contracts funded by the Australian Mineral Industries Re-
search Association Ltd. were an important factor in widening the activity
spectrum.
It would be very remiss of me if I failed to record my thanks and apprecia-
tion for the support and encouragement received from the managements of
both the Aeronautical Research Laboratories and the CSIRO Division of
Energy Technology (formerly the Division of Mechanical Engineering) dur-
ing my time of duty. I am especially indebted to the secretarial staff of the
latter for the manuscript typing, an arrangement approved by the Divisional
Chiefs, Dr. B. Rawlings and Dr. D. C. Gibson.
I am grateful to the University of New South Wales for allowing me to use
material from a Master of Engineering thesis submitted in 1954. The Institu-
tion of Engineers in Australia has kindly given permission for the use of
selected data from seven research papers published on my behalf in their
Transactions; these are referenced within.
Acknowledgment is also made to Dr. G. N. Patterson who initiated the
fan design approach developed herein. Messrs. M. C. Welsh, I. C. Shep-
herd, V. J. Smith, and Dr. R. Parker all contributed some input to the
finished work. My special thanks are extended to the above and to Mr. G. W.
Kipp for assistance in proofreading the galleys.
Finally the typing assistance, support, and tolerance displayed by my wife
during the manuscript preparation and publication periods is applauded.
R. ALLAN WALLIS
Melbourne, Australia
June 1983
Contents
Introduction 1
=
D Introduction to the Fluid Dynamics of Fans and Ducts 8
W
Boundary Layer and Skin Friction Relations 30
w
Duct Component Design and Losses 61
A
T Duct System Design and Development 137
O Airfoil Data for Blade Design 143
N
Introduction to Fan Design Methods 177
V
D Rotor: Momentum Considerations, Free Vortex Flow 184
O Rotor Blade Design 197
10 Rotor Losses 217
11 Stators: Design Considerations 230
12 Stator and Strut Support Losses 241
13 Ancillary Component Design 248
14 Overall Efficiency, Torque, Thrust, and Power 260
15 Design Optimization 264
16 Fan Materials, Mechanics, and Noise 277
17 Fan Applications 302
18 Design Examples 312
19 Rotor and Stator Analysis 324
20 Examples of Fan Analysis 336
21 Fan Testing—Commercial 344
22 Fan Testing—Developmental Research 361
23 Review of Design Assumptions and Limitations 390
Appendix A Approximate Design Procedures 396
Appendix B Diaphragm Mounted and Shrouded Fans 406
Appendix C Air Circulating Fans 409
Appendix D Airfoil Section Data 425
Notation 433
Index 439