D. J. TRITTON
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SECOND EDITION
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P O R D SCIENCE PUBLICATIONS
PHYSICAL FLUID DYNAMICS
PHYSICAL
FLUID DYNAMICS
Second Edition
D. J. Tritton
Formerly, Department of Physics, University of Newcastle upon Tyne
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British Library Cataloguing in Publication Data
Tritton, D. J.
Physical fluid dynamics-2nd
ed.
1. Fluid dynamics
I. Title
5329.05 QC151
Tritton, D. J.
Library of Congress Cataloging in Publication Data
Physical fluid dynamicsID. J. Tritton-2nd
Includes index.
Bibliography: p.
ed.
1. Fluid dynamics. I. Title
QC15 1 .T74 1988 5329.05-dc19
87-34162
ISBN 978-0- 19-854493-7 (Pbk)
Printed in Great Britain
on acid-free paper by
Biddles Ltd., King's Lynn, Norfolk
PREFACE TO THE SECOND EDITION
I have been gratified by the comment, received from many people, that
the first edition was a valuable addition to the range of textbooks on fluid
dynamics-mainly
its distinctive approach. This second
edition endeavours to retain that approach, whilst introducing topics that
have assumed greater importance since the first edition was prepared.
because of
The principal changes and additions are as follows. The discussion of
separation is extended-and given a chapter of its own (Chapter 13)-to
include a fuller explanation and to cover all cases, not just boundary
layer separation. The treatment of instabilities has been substantially
reorganized; the phenomenological description and the explanation of
linear stability theory are now more intermingled in a single chapter
(Chapter 17). BCnard convection is no longer used as an example in the
main discussion of instabilities, but is given a brief introduction in
Chapter 4 and a full treatment in Chapter 22; the treatment in the first
edition was rather fragmented, and there have been substantial advances
in our understanding since that material was written. The discussion is
extended in Chapter 23 to cover double diffusive convection. Partly as a
consequence of these changes, the material on other convection topics in
Chapters 4 and 14 is rearranged-but
covers much the same ground as
before. In the discussion of the structure of turbulent motion (Chapter
21) the parts concerned with large-scale motions (coherent structures)
have been completely rewritten. Chapter 24 discusses modern ideas
about 'chaos'-not,
strictly speaking a fluid dynamical topic, but certainly
one that students of fluid dynamics need to know about.
Outside the main text, the principal change is the addition of hints and
answers for the problems. I have mixed feelings about the value of these.
The temptation for a student to look at the hint too soon can be
irresistable. However, this addition has been urged on me by a number of
readers and on balance I now think that they are right.
There are quite a lot of minor changes. I have gone through the whole
text, considering whether clarification or updating was needed-and
bearing in mind the many helpful comments received from readers.
Illustrations have been replaced where more appropriate ones have
become available. But much remains unchanged; I hope that the right
balance has been struck between the dynamics of a new edition and
continuity with the old.
So many people have helped in one way or another that to list them all
vi
PREFACE TO THE SECOND SDITION
is impossible and to list some may be arbitrary. However, I have been
particularly helped by expert advice on some of the sections in Chapter
26 from: Professor D. Etling of the University of Hannover (Section
26.2); Dr H. Tsoar of the Ben Gurion University of the Negev (26.4); Dr
P. A. Davies of the University of Dundee (26.7); Mr R. G. Gawthorpe
of the Railway Technical Centre, Derby (26.10); Dr A. D. W. Jones of
B.P. Research Centre, Sunbury (26.11); Dr M. E. J. Holwill of King's
College London (26.12); and Dr R. P. Clark of the M.R.C. Clinical
Research Centre, Harrow (26.13).
I hope that the people who have helped with other parts of the book
will accept a blanket, but very sincere, thank you. Many people have
provided originals of photographs and diagrams, for which I am most
grateful. The originators of all photographs and sets of data are indicated
in the captions or by the references. Acknowledgements to bodies who
have given permission for the reproduction of copyright material are
listed separately.
In the preparation of the book I have been much helped by the
technical skills of Mrs D. Cooper, who draughted the new diagrams, Mr
J. Hunter and Mr G. Robb and the secretarial skills of Mrs L. Whiteford.
Finally, my thanks go to the staff of the Oxford University Press for
their friendly and efficient collaboration.
Newcastle upon Tyne
August 1987
FROM T H E PREFACE TO T H E FIRST
EDITION?
To classify a book as 'experimental' rather than 'theoretical' or as 'pure'
rather than 'applied' is liable to imply unreal distinctions. Nevertheless,
some classification is necessary to tell potential readers whether the book
is for them. In this spirit, this book mapbe said to treat fluid dynamics as
a branch of physics, rather than as a branch of applied mathematics or of
engineering. I have often heard expressions of the need for such a book,
and certainly I have felt it in my own teaching.
I have written it primarily for students of physics and of physics-based
applied science, although I hope others may find it useful. The book
differs from existing 'fundamental' books in placing much greater
emphasis on what we know through laboratory experiments and their
physical interpretation and less on the mathematical formalism. It differs
from existing 'applied' books in that the choice of topics has been made
for the insight they give into the behaviour of fluids in motion rather than
for their practical importance. There are differences also from many
existing books on fluid dynamics in the branches treated, reflecting to
some extent shifts of interest in recent years. In particular, geophysical
and astrophysical applications have prompted important fundamental
developments in topics such as convection, stratified flow, and the
dynamics of rotating fluids. These developments have hitherto been
reflected in the contents of textbooks only to a limited extent.
Much of the book is based on lectures I have given to final year
physics students at the University of Newcastle upon Tyne, though I have
substantially expanded parts of the material. I have also been influenced
by teaching fluid dynamics both at a more elementary level and also to
postgraduate students of geophysics and planetary physics. I have tried to
learn which approaches to various topics students find most informative,
and I hope this experience has led to improvements in what I have
written.
I have had the final year physics students particularly in mind when
deciding what background knowledge to assume of the reader. The
mathematical methods used should all be familiar to such students
(although substantial parts of the book would be intelligible to a reader at
t In this shortened version, the chapter and section numbers refer to the present edition.
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FROM THE PREFACE TO THE FIRST EDITION
an earlier mathematical stage). Also, it is not really paradoxical that a
book aimed at physics students should contain less explanation of basic
physics (such as related thermodynamics) than some other fluid dynamics
texts; knowledge of this can reasonably be assumed.
Nevertheless, I hope that the book will be of value to a variety of
other types of reader and I have tried to extend its usefulness wherever
this has been possible without distorting the primary aim. Workers in
widely various types of applied science need an understanding of the
phenomena of fluid motion. I have in mind particularly, but not solely,
geo- and planetary physicists (meteorologists and oceanographers as well
as students of planetary interiors), of whose needs I probably have the
most immediate appreciation. Where fluid dynamical topics are taught as
part of a geophysics course, I believe that this should be a suitable
textbook. I believe also that postgraduate students and other research
workers, faced with a project involving fluid dynamics, should find this
book of value. It is not uncommon for otherwise interesting geophysical
papers to be marred by the employment of fluid dynamical concepts in a
way that shows serious misunderstanding of their significance. But these
misunderstandings are not surprising in the absence of convenient sources
of information. Such readers should not imagine that there are easy
short-cuts to an understanding of the phenomena of fluid motion, but I
trust that this book may make the long route a little less arduous.
The choice of topics in a book of this sort must be controversial. The
size of the subject necessitates many arbitrary omissions. The reader
wishing to discover just what is included and what is omitted may find it
useful to refer not only to the contents list but also to Section 1.2. The
major limitation is the restriction to incompressible flow. This will, I
know, make the book inadequate for some courses. Compressible flow is,
however, such a large topic that it really requires a book of its own; just a
chapter would perhaps do it more of an injustice than total omission.
Even within the limitation to incompressible flow, I am much aware of
omissions that some readers will regret. What I hope I have achieved is a
text giving students sufficient knowledge of the basic concepts of fluid
dynamics and sufficient insight into the consequences of these concepts
that they will be able to use other (probably more advanced) sources to
obtain information that is omitted here.
The systematic development of the subject occupies Chapters 5 to 24.
After the introduction in Chapter I, Chapters 2 to 4 treat three particular
topics in a descriptive (thought hopefully not too superficial) way. These
topics have been placed ahead of the systematic treatment for two
reasons. Primarily they are intended to give the reader some understand-
ing of the type of phenomena with which one is concerned; it is a long
haul through the basic concepts of Chapters 5 to 8 if one does not know