JET PROPULSION

JET PROPULSION A Simple Guide to the Aerodynamic and Thermodynamic Design and Performance of Jet Engines This is the second edition of Cumpsty’s excellent self-contained introduction to the aerodynamic and thermodynamic design of modern civil and military jet engines. Through two engine design projects, first for a new large passenger air- craft, and second for a new fighter aircraft, the text introduces, illustrates and explains the important facets of modern engine design. Individual sections cover aircraft requirements and aerodynamics, principles of gas turbines and jet engines, elementary compressible fluid mechanics, bypass ratio selection, scal- ing and dimensional analysis, turbine and compressor design and characteristics, design optimisation, and off-design performance. The book emphasises prin- ciples and ideas, with simplification and approximation used where this helps understanding. This edition has been thoroughly updated and revised, and includes a new appendix on noise control and an expanded treatment of com- bustion emissions. It is suitable for student courses in aircraft propulsion, but also an invaluable reference for engineers in the engine and airframe industry. 无水印完整版本下载：www.n-ebook.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com BLANK PAGE 无水印完整版本下载：www.n-ebook.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com JET PROPULSION A Simple Guide to the Aerodynamic and Thermodynamic Design and Performance of Jet Engines NICHOLAS CUMPSTY University of Cambridge 无水印完整版本下载：www.n-ebook.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com © Cambridge University Press 2003 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 2003 Printed in the United Kingdom at the University Press, Cambridge Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, Sa~ Cambridge University Press The Edinburgh Building, Cambridge CB2 8RU, UK Published in the United States of America by Cambridge University Press, NewYork www.cambridge.org Information on this title:www.cambridge.org/9780521541442 This publication is in copyright. Subject to statutory exception A catalogue record for this ppublication is available from the British Library ISBN 978-0 -521-54144-2 paperback o Paulo, Delhi CAMBRIDGE UNIVERSITY PRESS Seventh printing 2009 Cambridge University Press has no responsibility for the persistence or accuracy factual information given in this work are correct at the time of first printing but Cambridge Universtiy Press does not guarantee the accuracy of such information thereafter. accurate or appropriate. Information regarding prices, travel timetables and other and does not guarantee that any content on such websites is, or will remain, of URLs for external or third-party internet websites referred to in this publication, 无水印完整版本下载：www.n-ebook.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com CONTENTS Preface vii Glossary xi Nomenclature xiv Part 1 Design of Engines for a New 600-seat Aircraft 1 The New Large Aircraft – Requirements and Background 3 2 The Aerodynamics of the Aircraft 15 3 The Creation of Thrust in a Jet Engine 25 4 The Gas Turbine Cycle 30 5 The Principle and Layout of Jet Engines 47 6 Elementary Fluid Mechanics of Compressible Gases 60 7 Selection of Bypass Ratio 69 8 Dynamic Scaling and Dimensional Analysis 80 9 Turbomachinery: Compressors and Turbines 94 10 Overview of the Civil Engine Design 108 Part 2 Engine Component Characteristics and Engine Matching 11 Component Characteristics 113 12 Engine Matching Off-design 143 Part 3 Design of Engines for a New Fighter Aircraft 13 A New Fighter Aircraft 179 14 Lift, Drag and the Effects of Manoeuvring 189 15 Engines for Combat Aircraft 201 16 Design Point for a Combat Engine 221 17 Combat Engines Off-design 242 18 Turbomachinery for Combat Engines 262 Part 4 Return to the Civil Transport Engine 19 A Return to the Civil Transport Engine 269 20 To Conclude 283 Appendix: Noise and its Regulation 289 Bibliography 297 References 300 Index 301 Design sheets for New Large Civil Aircraft and New Fighter Aircraft 304 无水印完整版本下载：www.n-ebook.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com Blank Page 无水印完整版本下载：www.n-ebook.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com PREFACE TO SECOND EDITION The book has been well received and Cambridge University Press approached me with the invitation to bring out a second edition. This was attractive because of the big events in aerospace, most significantly the decision by Airbus Industrie at the end of 2000 to launch their new large aircraft, the A380. This meant that some changes in the first ten chapters were needed. Another major development is the decision to develop an American Joint Strike Fighter, the F-35. Another more personal change took place when I left academia to become Chief Technologist of Rolls-Royce from the beginning of 2000. It should be noted, however, that the character and ideas of this second edition remain those of the university professor who wrote the first edition and do not reflect my change of role. The aim and style of the book is unchanged. The primary goal of creating understanding and the emphasis remains on simplicity, so far as this is possible, with the extensive use of relevant numerical exercises. In a second edition I have taken the opportunity to update a number of sections and to include some explanatory background on noise; noise has become a far more pressing issue over the last four or five years. The book remains, however, very similar to the first edition and, in particular, numerical values have been kept the same and the exercises have not been changed. Fortunately I do not think that the changes are not large enough to mislead the reader. In writing the first edition I was grateful for the help of many people. Mention should be made here of help from Professor Mike Owen of the University of Bath and from the students who took courses given at Rensselaer Polytechnic in Hartford Connecticut, leading to changes to the 2000 revision of the first edition. For the second edition I would like to acknowledge the additional help received in preparing the second edition from colleagues in Rolls-Royce, notably Nigel Birch, Andrew Bradley, Chris Courtney, Jason Darbyshire, Peter Hopkins, Andrew Kempton, Paul Madden, Steve Morgan, Mike Provost, Joe Walsh and Eddie Williams. From outside the Company the suggestions of George Aigret were gratefully received. Comments and corrections from readers will continue to be welcomed. PREFACE TO FIRST EDITION This book arose from an elementary course taught to undergraduates, which forms the first ten chapters concerned with the design of the engines for a new 600-seat long range airliner. Introductory undergraduate courses in thermodynamics and fluid mechanics would provide the reader with the required background, but the material is also presented in a way to be accessible to any graduate in engineering or physical sciences with a little background reading. The coverage is deliberately restricted almost entirely to the thermodynamic and aerodynamic aspects of jet propulsion, a large topic in itself. The still larger area associated with mechanical aspects of 无水印完整版本下载：www.n-ebook.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com viii Preface engines is not covered, except that empirical information for such quantities as maximum tip speed are used, based on experience. To cover the mechanical design of engines would have required a much bigger book than this and would have required a mass of knowledge which I do not possess. In preparing the course it was necessary for me to learn new material and for this I obtained help from many friends and colleagues in industry, in particular in Rolls-Royce. This brought me to realise how specialised the knowledge has become, with relatively few people having a firm grasp outside their own speciality. Furthermore, a high proportion of those with the wide grasp are nearing retirement age and a body of knowledge and experience is being lost. The idea therefore took hold that there is scope for a book which will have wider appeal than a book for students – it is intended to appeal to people in the aircraft engine industry who would like to understand more about the overall design of engines than they might normally have had the opportunity to master. My ambition is that many people in the industry will find it useful to have this book for reference, even if not displayed on bookshelves. The original course, Chapters 1–10, was closely focused on an elementary design of an engine for a possible (even likely) new large civil aircraft. Because the intention was to get the important ideas across with the least complication, a number of simplifications were adopted, such as taking equal and constant specific heat capacity for air and for the gas leaving the combustor as well as neglecting the effect of cooling air to the turbines. Having decided that a book could be produced, the scope was widened to cover component performance in Chapter 11 and off-design matching of the civil engine in Chapter 12. Chapters 13 – 18 look at various aspects of military engines; this is modelled on the treatment in Chapters 1–10 of the civil engine, postulating the design requirement for a possible new fighter aircraft. In dealing with the military engine some of the simplifications deliberately adopted in the early chapters are removed; Chapter 19 therefore takes some of these improvements from Chapters 13 – 18 to look again at the civil engine. Throughout the book the emphasis is on being as simple as possible, consistent with a realistic description of what is going on. This allows the treatment to move quickly, and the book to be brief. But more important it means that someone who has mastered the simple formulation can make reasonably accurate estimates for performance of an engine and can estimate changes in performance with alteration in operating condition or component behaviour. Earlier books become complicated because of the use of algebra; furthermore to make the algebra tractable frequently forces approximations which are unsatisfactory. The present book uses arithmetic much more – by taking advantage of the computer and the calculator the numerical operations are almost trivial. The book contains a substantial number of exercises which are directed towards the design of the civil engine in the early chapters and the military engine in the later chapters. The exercises form an integral part of the book and follow, as far as possible, logical steps in the design of first the civil engine and then later the military combat engine. Many of the insights are 无水印完整版本下载：www.n-ebook.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com Preface ix drawn from the exercises and a bound set of solutions to the exercises may be obtained from the author. Because Chapters 1–10 were directed at undergraduates there are elementary treatments of some topics (most conspicuously, the thermodynamics of gas turbines, compressible fluid mechanics and turbomachinery) but only that amount needed for understanding the remainder of the treatment. I decided to leave this elementary material in, having in mind that some readers might be specialists in areas sufficiently far from aerodynamics and thermodynamics that a brief but relevant treatment would be helpful. ACKNOWLEDGEMENTS It is my pleasure to acknowledge the help I have had with this book from my friends and colleagues. The largest number are employed by Rolls-Royce (or were until their retirement) and include: Alec Collins, Derek Cook, Chris Freeman, Keith Garwood, Simon Gallimore, John Hawkins, Geoffery Hodges, Dave Hope, Tony Jackson, Brian Lowrie, Sandy Mitchell, James Place, Paul Simkin, Terry Thake and Darrell Williams. Amongst this group I would like to record my special gratitude to Tim Camp who worked through all the exercises and made many suggestions for improving the text. I would also like to acknowledge the late Mike Paramour of the Ministry of Defence. In the Whittle Laboratory I would like to record my particular debt to John Young and also to my students Peter Seitz and Rajesh Khan. I am also grateful for the help from other students in checking late drafts of the text. In North America I would like to mention Ed Greitzer and Jack Kerrebrock (of the Gas Turbine Laboratory of MIT), Bill Heiser (of the Air Force Academy), Phil Hill (of the University of British Columbia), Bill Steenken and Dave Wisler (of GE Aircraft Engines) and Robert Shaw. Above all I would like to express my gratitude to Ian Waitz of the Gas Turbine Laboratory of MIT who did a very thorough job of assessing and weighing the ideas and presentation – the book would have been very much the worse without him. In addition to all these people I must also acknowledge the help and stimulus from the students who took the course and the people who have added to my knowledge and interest in the field over many years. 无水印完整版本下载：www.n-ebook.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com x Preface THE EXERCISES An important part of the book are exercises related to the engine design. To make these possible it is necessary to assume numerical values for many of the parameters, and appropriate values are therefore assumed to make the exercises realistic. These values are necessarily approximate, and in some cases so too is the model in which they are used. The answers to the exercises, however, are given to a higher level of precision than the approximations deserve. This is done to assist the reader in checking solutions to the exercises and to ensure some measure of consistency. The wise reader will keep in mind that the solutions are in reality less accurate than the number of significant figures seems to imply. The usefulness of the book will be greatly increased if the exercises are undertaken. In some cases one exercise leads to another and a few simple calculations on a hand-held calculator suffice. In others it is desirable to carry out several calculations with altered parameters, and such cases call out of a computer and spread sheet. SOLUTIONS TO THE EXERCISES Solutions to all the exercises may be obtained from the publisher by e-mailing solutions@cambridge.org 无水印完整版本下载：www.n-ebook.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com GLOSSARY afterburner a device common in military engines where fuel is burned downstream of the turbine and upstream of the final propelling nozzle. Also known as an augmentor or as reheat. aspect ratio the ratio of one length to another to define shape, usually the ratio of span to chord blades the name normally given to the aerofoils in a turbomachine (compressor or turbine). Sometimes stationary blades are called stator vanes (or just vanes) and rotor blades are called buckets. booster a name given to compressor stages on the LP shaft in two-shaft engines. The booster stages only affect the core flow. bypass engine an engine in which some of the air (the bypass stream) passes around the core of the engine. The bypass stream is compressed by the fan and then accelerated in the bypass stream nozzle. These are sometimes called turbofan engines or fan engines. bypass ratio the ratio of the mass flow rate in the bypass stream to the mass flow rate through the core of the engine. chord the length of a wing or a turbomachine blade in the direction of flow. combustor also known as a combustion chamber. The component where the fuel is mixed with the air and burned. compressor the part of the engine which compresses the air, a turbomachine consisting of stages, each with a stator and rotor row. core the compressor, combustion chamber and turbine at the centre of the engine. The core turbine drives only the core compressor. A given core can be put to many different applications, with only minor modifications, so it could form part of a high bypass ratio engine, a turbojet (with zero bypass ratio) or part of a land-based power generation system. The core is sometimes called the gas generator. drag the force D created by the wings, fuselage etc. in the direction opposite to the direction of travel. fan the compressor operating on the bypass stream; normally the pressure ratio of the fan is small, not more than about 1.8 for a modern high bypass civil engine (in one stage with no inlet guide vanes) and not more than about 4.5 in a military engine in two or more stages. gross thrust the thrust FG created by the exhaust stream without allowing for the drag created by the engine inlet flow; for a stationary engine the gross thrust is equal to the net thrust. HP the high-pressure compressor or turbine are part of the engine core. They are mounted on either end of the HP shaft. In a two-shaft engine they form the core spool. incidence sometimes called angle of attack, is the angle at which the wing is inclined to the direction of travel or the angle at which the inlet of a compressor or turbine blade is inclined to the inlet flow direction. 无水印完整版本下载：www.n-ebook.com Doc uCo m P DF Tria l ww w.pd fwiz ard. com xii Glossary IP the intermediate-pressure compressor or turbine, mounted on the IP shaft. There is only an IP shaft in a three-shaft engine. jetpipe the duct or pipe downstream of the LP turbine and upstream of the final propelling nozzle. LCV the lower calorific value of the fuel; the energy released per unit mass of fuel in complete combustion when the products are cooled down to the inlet temperature but none of the water vapour is allowed to condense. lift the force L created, mainly by the wings, perpendicular to the direction of travel. LP the low-pressure compressor and turbine are mounted on either end of the LP shaft. Combined they form the LP spool. nacelle the surfaces enclosing the engine, including the intake and the nozzle. net thrust the thrust FN created by the engine available to propel the aircraft after allowing for the drag created by the inlet flow to the engine. (Net thrust is equal to gross thrust minus the ram drag.) ngv the nozzle guide vane, another name for the stator row in a turbine. nozzle a contracting duct used to accelerate the stream to produce a jet. In some cases for high performance military engines a convergent-divergent nozzle may be used. payload the part of the aircraft weight which is capable of earning revenue to the operator (can be freight or passengers). pylon the strut which connects the engine to the wing. ram drag the momentum of the relative flow entering an engine. sfc specific fuel consumption (actually the thrust specific fuel consumption) equal to the mass flow rate of fuel divided by net thrust. The units should be in the form (kg/s)/kN, but are often given as lb/h/lb or kg/h/kg. specific thrust the net thrust per unit mass flow through the engine, units m/s. spool used to refer to the compressor and turbine mounted on a single shaft, so a two-spool engine is synonymous with a two-shaft engine stagnation stagnation temperature is the temperature which a fluid would have if brought to rest adiabatically. The stagnation pressure is the pressure if the fluid were brought isentropically to rest. Stagnation quantities depend on the frame of reference and are discussed in Chapter 6. static static temperature and pressure are the actual temperature and pressure of the fluid, in contrast to the stagnation qua