Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More Information
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Cambridge University Press 978-0-521-13289-3 - Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More information UNDERSTANDING FLUID FLOW © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-13289-3 - Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More information © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-13289-3 - Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More information African Institute of Mathematics Library Series The African Institute of Mathematical Sciences (AIMS), founded in 2003 in Muizenberg, South Africa, provides a one-year postgraduate course in mathematical sciences for students throughout the continent of Africa. The AIMS LIBRARY SERIES is a series of short innovative texts, suitable for self-study, on the mathematical sciences and their applications in the broadest sense. Editorial Board Professor J. Banasiak (University of KwaZulu-Natal) Professor A.F. Beardon (University of Cambridge) Professor P. Deift (Courant Institute of Mathematical Sciences) Professor P.E. Dorey (Durham University) Professor B.W. Green (University of Stellenbosch) Professor F.W. Hahne (The Director, AIMS) Professor A. Iserles (University of Cambridge) Professor P.E. Kopp (University of Hull) Professor P. Sarnak (Institute for Advanced Study Princeton) Dr. T. Tokieda (University of Cambridge) Professor N.G. Turok (University of Cambridge and Perimeter Institute, Ontario) © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-13289-3 - Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More information © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-13289-3 - Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More information AIMS Library Series UNDERSTANDING FLUID FLOW GRAE WORSTER Institute of Theoretical Geophysics Department of Applied Mathematics and Theoretical Physics University of Cambridge © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-13289-3 - Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More information The Water Club, Beach Road, Granger Bay, Cape Town 8005, South Africa Cambridge University Press is part of the University of Cambridge. It furthers the University’s mission by disseminating knowledge in the pursuit of education, learning and research at the highest international levels of excellence. www.cambridge.org Information on this title: www.cambridge.org/ 9780521132893 © Cambridge University Press 2009 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2009 A catalogue record for this publication is available from the British Library isbn 978-0-521-13289-3 Paperback Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-13289-3 - Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More information Contents Preface page xi 1 Building intuition 1 Viscous fluids 1 Normal stress 3 The no-slip condition 3 A viscous gravity current 4 Dynamic viscosity 5 Tangential shear stress 6 Assignment 1 7 2 Parallel viscous flow 9 Momentum equation 9 Boundary conditions 10 Parallel flow in a channel 11 Poiseuille flow in a pipe 13 Film flow on a vertical surface 15 Couette versus Poiseuille 16 Unsteady parallel viscous flows 18 Kinematic viscosity 22 Viscous boundary layers 23 3 Viscous gravity currents 25 Scaling analysis 27 Velocity profile and volume flux 27 Conservation of mass 28 © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-13289-3 - Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More information Contents Similarity solution 29 Assignment 2 31 4 Equations of flow 37 The Navier–Stokes momentum equation 37 Hydrostatic and dynamic pressure 39 Mass conservation 40 Stream functions 42 Scaling the Navier–Stokes equations 45 Stagnation-point flow 49 Viscous boundary layer 50 Bernoulli’s theorem 54 The momentum integral 57 5 Interactions between linear flows 63 Linear flow 63 Pure straining flow 64 Vorticity 65 The vorticity equation 65 Vortex stretching 66 Dissipation and generation of vorticity 68 6 Flows around rigid objects 71 Irrotational incompressible potential flow 71 Potential flow past a sphere 71 The force in potential flow 73 Flow separation and drag 74 The origin of separation 75 Circulation around a rigid body 77 Irrotational flow with circulation – causing lift 79 7 Waves and instability 83 Energy conservation in potential flow 83 Waves on deep water 84 Properties of deep-water waves 86 Ship wakes 88 Group velocity 90 © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-13289-3 - Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More information Contents Hydrodynamic instability 92 Turbulence 98 Epilogue 100 Bibliography 101 Index 103 © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-13289-3 - Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More information © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-13289-3 - Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More information xi Preface This book is an account of lectures that I gave at AIMS (the African Institute of Mathematical Sciences) in 2008, which were developed from two earlier courses I had given there in 2004 and 2006. I did not set out to write a textbook but rather to present a diary, summarising and reviewing what I had tried to convey to the students in the hour or two immediately preceding writing. This reflects the fact that lectures at AIMS are dynamic, interactive sessions and I had prepared little by way of formal lecture notes in advance. To be sure, there was some didactic delivery of ideas, but that lecturing activity was interspersed with problem-solving activities and many, many questions from stu- dents so that the educational process was much more of a conversation than is typical of most university courses I have given. Having now put this material in writing, I hope that it might interest and inspire students and teachers alike but will not constrain or encourage future lecturers at AIMS or elsewhere to teach rigidly from the book. Where, in the course of writing, I discovered some small point that I had omitted to mention or some additional clarification or illustration that I felt would be helpful, I allowed myself to include it. Other than that, I have made no attempt to expand upon what I taught or to provide a comprehensive introduction to fluid dynamics. A student interested in pursuing the ideas further should consult any of the many excellent texts that exist in this subject, a few of which are described in the Bibliography. In my view, fluid dynamics as a discipline sits squarely between physics and mathematics. It is important to understand the physical interactions involved well enough to codify them within mathematical © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-13289-3 - Understanding Fluid Flow: AIMS Library Series Grae Worster Frontmatter More information xii Preface equations, and to have sufficient mathematical insight to know whether the equations are likely to be manageable. The equations must then be solved, often by making approximations with enough physical insight to know whether the important interactions have been retained, and with enough mathematical rigour to have confidence in the resulting predictions. And finally, the mathematical solution must be interpreted in a way that sheds light on the physical problem being studied. I tried to convey that balance in the course, with the result that this is neither a physics text nor a mathematics text but a text aimed at understanding fluid flow from fundamental physical ideas explained and developed by mathematical studies. I anticipate that readers will have a basic understanding of Newto- nian dynamics, and be familiar with ordinary differential equations and vector calculus to the level usually taught in introductory undergraduate courses. The first two times that I lectured at AIMS, I shared the three-week course with another lecturer: Daya Reddy from the University of Cape Town in 2004 and Keith Moffatt from Cambridge University in 2006. I nevertheless wanted my half course to be complete in itself and to convey something meaningful about fluid dynamics as an important topic of current research to students who had never met the subject before. I felt it important that the students learn about real, viscous fluids, to have a taste of analytical, numerical and experimental approaches to understanding and quantifying the flow of fluids, and to experience the satisfaction and some of the limitations