5 thermodynamics of aircraft jet engines

768 Pages·2014·12.35 MB·English

SECOND EDITION
MECHANICS AND
THERMODYNAMICS
OF PROPULSION
PHILIP G. HILL
University of British Columbia
CARL R. PETERSON
Massachusetts Institute of Technology
Edition entitled lVlechanics And ru,0m1.,,11m. Second Edition,
Peterson, Carl, as Prentice Hall,
© 1992,
lmli:m edition published by Dorling Kindersley Ind.ia Pvt. Ltd. Copyright© 20HJ
AH reserved. This book is sold
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1SBN 978-81-3 17-295 l-9
First
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This edition is in lndia and is authorized sale in lndia, Bangladesh,
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REFACE
The basic premise of this book is that a few fundamental physical
rightly applied, can provide students of mechanical and aeronautical engineering
with a deep understanding of all modes of aircraft and spacecraft propulsion.
More-that they can lead directly to usefully assessments of perfor
mance; and still more-that they can illuminate possibilities for improvement.
Doubtless, it is only at a fundamental level that one can properly address not only
the of how and things work but also the more challenging questions
of and how they can be
It would not do, of course, to stress fundamental principles exclusively;
in application do the basic ideas really come alive to stimulate both analysis and
invention. It is sometimes astonishing to see how a few basic ideas can reduce
what would otherwise be an overwhelming mass of information into under
stood and manageabie categories. Application of basic principles to specific engi
neering objectives can reward the student not only with a valuable appreciation of
their practical significance but also with a much deeper understanding of the
principles themselves.
The first edition of this book has been used hy thousands of engineering stu
dents over the last twenty-five years, but it is now time for a new edition. Not
that the basic principles of propulsion have changed, but over this period the
practical development of aircraft and propulsion has been truly spec-
tacular. The subject is now more interesting than it ever was before. It
therefore seems appropriate to offer a new edition that can not reflect on the
great achievements of the recent but also assess the reasons why we may yet
great developments.
In preparing the second edition, one has been to provide a wide
range of new illustrative material on modern aircraft and rocket engines. A sec-
ond has been to present clearer of physical A
a much greater range of statements at the end of each
to introduce
iii
iv PREFACE
Today students have marvelous computers and graphics with which to cal
culate and display the implications of ideas that should control new designs. Real
istic treatment of physical properties and mechanisms is quite easily possible
within an appropriate time allotment. Hence this new edition encourages stu
dents, through design examples and problem statements, to consider the possibil
ities of preliminary design so as to identify physical possibilities and limitations
as clearly as possible and to determine the consequences of uncertainty. This is
not to say that in an introductory propulsion course one can use the complete
Navier-Stokes equations to design turbomachinery, for example. But it does mean
that the fluid mechanics of turbomachinery can be treated in realistic, albeit
more approximate, simple ways that provide insight into how turbomachines work
and how they can be designed.
Among the resources now available to students of propulsion are computer
codes that they can use .knowledgeably and critically to display the characteristics
of specific important phenomena. One of these is the STANJAN code developed
by W. C. Reynolds of Stanford University, for fast, versatile determination of the
high-temperature equilibrium composition of cbmbustion products. Treatment of
boundary layer separation (which places such an important limitation on turbo
machine behavior) is now quite easy, in the two-dimensional approximation, with
the aid of a personal computer and the equatior,s presented in the text. One can
also readily use elementary computer procedures to take into account the effects
of high-temperature variations on the specific heat of gases. Thus the power of
the student to explore physical phenomena and design possibilities has in recent .
years been greatly enhanced.
The essentially difficult problem is that within a given course there is only so
much time to take up new ideas. The book contains more than any one course
can contain, so a choice must be made.
Part 1 of this text consists mainly of a review of those topics in thermo
dynamics, combustion, and fluid mechanics that are of vital importance to
propulsion engines. One chapter reviews the thermodynamics of flow through
control volumes with or without chemical reaction. Because of the prime signifi
cance of high-speed flows, a brief chapter is devoted entirely Jo review of com
pressible flows, Mach number, and shock waves. Because of the extremely
important design limitation due to boundary layers, one chapter is concerned
with boundary layer growth, separation, and heat transfer.
Part 2 of .the teif focuses on air-breathing turbine engines exclusively. First"
come analyses of propulsion efficiency, cycle performance, and the rationale for
various types of turbine engines. Tlm is followed by description and analysis of
the ways in which successful flow behavior can be obtained in inlets, burners, and
nozzles, then by detailed examination of the aerodynamics and performance of
compressors and turbines. The development of high-flow-rate, high-efficiency
compressors has for long been one of the most important challenges in turbine
engine development, so these chapters present the topics of axial and centrifugal
compressor (as well as turbine) aerodynamics in some depth. In each case the
first section of the chapter deals mainly with the questions of why and how this
PREFACE V
turbomachine works; the with the physical factors that limit its perfor-
mance and with how these may be quantified; and the with a
preliminary design procedure. The first section of each chapter would make
a complete unit if there is no time to take up the second and third
sections. (If one wishes to include both rockets and air-breathing engines in a
one-term course, this kind of selection might be essential.)
Part 3 of the text is devoted to rocket propulsion. Chapter 10 presents an
elementary treatment of rocket vehicle dynamics to demonstrate the s;ignificance
of specific impulse and other variables and also to show how to decide on propul
sion requirements for space missions. The latter requires some attention to the
trajectories of space vehicles and the conditions under which the propulsion
system may be optimized. Chemical rockets are the subject of Chapters 11,
and 13. Chapter 11 takes up those fundamental matters that govern the design
and optimization of rocket nozzles; aerodynamics and heat transfer are two
of the most important concerns. The next chapter analyzes the important
features of liquid- and solid-propellant combustion. Key topics here include
product mixture dissociation and equilibrium or nonequilibrium ( or even two
phase) expansion processes. Chapter 13 focuses on the turbomachinery for a
rocket vehicle and shows how one can make preliminary design decisions
about system configuration, size, and speed for specified propellant flow rates
and pressure rises.
Chapter 14 is devoted to the special feature of electrical propulsion, taking
up fundamental considerations of why and how electrostatic, electrothermal, and
electromagnetic propulsion can be used to best advantage.
A one-term course on rockets might consist of appropriate review of material
in Chapters 2, 3, and 4 and a treatment of selected topics from Chapters 10
through 14.
A substantiai effort has been made to improve the number and quality of
problem statements at the end of each chapter. Objectives have been that each
problem statement should refer to a substantial exercise that will illuminate an
important question; that each problem should be doable (and that the average
student shouid not be left baffled on how to start); that certain problem state
ments should, with guidance, take the student beyond what is clearly spelled out
in the text; and that certain of them should be directed to preliminary design cal
culations feasible on a personal computer. However, no student should feel
obliged to solve all the problems in a given chapter.
The mathematical portions of the text assume a knowledge of calculus, but
mathematical complication has been minimized so that the reader can clearly dis
cern physical principles. So much can be learned from steady-flow control volume
analyses that these have been used again and again in the study of one- and two
dimensional compressible and incompressible viscous and inviscid flows.
To make the text as readable as possible, the equation sets derived pre-
liminary design have been relegated to the appendixes. The equations provided
should be sufficient to allow exploration of many more design options than are
specifically discussed in the text.
vi PREFACE
Referring back to the preparation of the first edition, the authors again
would like to record our indebtedness to the late Edward S. Taylor, who was our
teacher, critic, and friend during our years of association in the M.I.T. Gas Tur
bine Laboratory. We originally wrote the text largely as a result of his encourage
ment, and his influence will still be recognizable in some of the sections.
Throughout the text are several references to the work of J. H. Keenan
and A.H. Shapiro. Their expositions of thermodynamics and fluid mechanics
were so enlightening to us as students that they have heavily influenced our whole
approach.
In the preparation of this second edition, the following people gave very
helpful advice and encouragement: Alexander Bryans, Nicolas Cumpsty, John
Denton, Edward Greitz~r, Sir William Hawthorne, William Horne, Herbert
Saravanamuttoo, George Serovy, and David Wilson, as well as the anonymous re
viewers who pointed strongly and helpfully .in the direction of needed improve
ments. I thank them all very much.
Cl<1ire Eatock, Bernie Gregoire, David Kenny, Joyce Lincoln, David Long,
J. A. J. Rees, and Joe Stangeland helped greatly with provision of engine illustra
tions and data. They too deserve special thanks.
Marguerite, my wife, did the word processing and text assembly in such a
skillful way that she transformed the whole task from difficulty to pleasure. But
no acknowledgment could possibly state all that I owe to her.
Churchill College, Cambridge, P.G.H.
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PART 1 l
The Jet 3
u Introductio1'1 3
1.2 Fluid Momentum and Reaction Force 4
1.3 Rockets 8
1.4
1.5 and 16
References 22
2 Mechanics and of Fluid Flow 23
2J 23
2.2
L3
2.4
Chemical Reactions
Problems 56
References 62
3 Steady One-Dimensiom:i! Flow of a Perfect Gas 65
3.1 Introduction 65
3.2 General One-Dimensional Flow of a Perfect Gas 66
3.3 Fiow 69
3.4 Flow 72
3.5 Frictionless Constant-Area Flow with ~"-·~··-·
74
3.6 Constant-Area Flow with Friction 77
Shocks
Problems 88
References 92
viii CONTENTS
Chapter 4 Boundary Layer Mechanics and Heat Transfer 93
4.1 Introduction 93
4.2 The Boundary Layer Equations 101
4.3 Laminar Boundary Layer Calculations 107
4.4 The Turbulent Boundary Layer 111
4.5 Boundary Layer Heat Transfer 124
Problems 130
References 137
PART 2 Air-Breathing Engines 139
Chapter 5 Thermodynamics of Aircraft Jet Engines 141
5.1 Introduction 141
5.2 Thrust and Efficiency 146
5.3 The Ramjet 155
5.4 Turbojet Engines 164
5.5 Turbofan Engines 177
5.6 Turboprop and Turboshaft Engines 189
5.7 Typical Engine Performance 196
5.8 Engine-Aircraft Matching 202
Problems 208
References 216
Chapter 6 Aerothermodynamics of Inlets, Combustors, and Nozzles 217
6.1 Introduction 217
6.2 Subsonic Inlets 218
6.3 Supersonic Inlets 226
6.4 Gas Turbine Combustors 242
6.5 Afterburners and Ramjet Combustors 257
6.6 Supersonic Combustion 262
6.7 Exhaust Nozzles 264
Problems 269
References 273
Chapter 7 Axial Compressors 275
7.1 Introduction 275
7.2 Angular Momentum 277
7.3 Work and Compression 282
7.4 Characteristic Performance of a Single Compressor Stage 288
7.5 Characteristic Performance of a Multistage
Axial Compressor 294
7.6 Boundary Layer Limitations 303
7.7 Compressor Efficiency 319
7.8 Degree of Reaction 330
7.9 Radial Equilibrium 332
CONTENTS ix
7.10 Design of a Subsonic Axial Compressor 336
7.11 Transonic Fan Stage 345
Problems 355
References 364
8 Axial Turbines 367
8.1 Introduction 367
8.2 The Axial Turbine Stage 370
8.3 Stage Efficiency 377
8.4 Rotor Blade and Disc Stresses 384
8.5 Blade Cooling 393
8.6 Turbine Performance 400
8.7 Turbine and Compressor Matching 402
8.8 Turbine Stage Design 406
Problems 414
References 423
Chapter 9 The Centrifugal Compressor 425
9.1 Introduction 425
9.2 Centrifugal Compressor Stage Dynamics 427
9.3 The Inducer and Impeller 435
9.4 The Diffuser 445
9.5 Performance Characteristics 451
9.6 Centrifugal Compressor Stage Design 453
Problems 460
References 465
PART 3 Rocket Engines 467
Chapter 10 Performance of Rocket Vehicles 469
10.1 Introduction 469
10.2 Static Performance 4 70
10.3 Vehicle Acceleration 472
10.4 Chemical Rockets 4 78
10.5 Electrical Rocket Vehicles 490
10.6 Space Missions 495
Problems 508
References 512
Chapter 11 Chemical Rocket Thrust Chambers 513
11.1 Introduction 513
11.2 Performance Characteristics 515
11.3 Nozzles 520
11.4 Rocket Heat Transfer ·5 41