SECOND EDITION
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`MECHANICS AND
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`THERMODY NAMICS
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`OF PROPULSION
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`PHILEP G. HELL
`University of British Columbia
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`CARL R. PETERSON
`Massachusetts Institute of Technology
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`UTC-2024.001
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`GEVV. UTC
`Trial IPR2016-00952
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`UTC-2024.001
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`GE v. UTC
`Trial IPR2016-00952
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`Original Edition entitled Mechanics /.1/m’ T/iemiodynaiiiics OfPr0/)1/l.s'i0n, Second Edition, by Hill,
`Philip; Peterson, Carl, published by Pearson Education, Inc, publishing as Prentice Hall, Copyright
`© 1992.
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`Indian edition published by Dorling Kindersley India Pvt. Ltd. Copyright © 2610
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`All rights reserved. This book is sold subject to the condition that it shall not, by way of trade or
`otherwise, be lent, resold, hired out, or otherwise circulated. without the publisher’s prior written
`consent in any form of binding or cover other than that~in which it is published and without a similar
`condition including this condition being imposed on the subsequent purchaser and without limiting
`the rights under copyright reserved above. no part of this publication may be reproduced, stored in or
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`introduced into a retrieval system, or
`transmitted in any form or by any means (electronic,
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`mechanical, photocopying, recording or otherwise), without the prior written permission of both the
`copyright owner and the above—m entioned publisher ofthis book.
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`lSBN 978-SI-317-2951-9
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`First Impression, 2010
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`Nineteenth Impression, 2013
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`Twentieth Impression, 2014
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`This edition is mtImiftictzu‘ei] in imlizi am! is ziz1tl10rizett' for sale onh; in Imliri, Baiigitiricsii,
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`Blinmn, Pakistan, Nepal, Sri Ltinkiz am] the Maldives. Circzilritiaii aftiiis edition outside oft/iesc
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`territories is UNA UTHORIZED.
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`Published‘ by Dorling Kindersley (India) Pvt. Ltd. licensees of Pearson Education in South Asia.
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`Head Ottice: 7”‘ Floor. knowledge Boulevard, A-8(A) Sector—62, Noida (U.P) 201309, India
`Registered Otlicez I
`1 Community Centre. Panchsheel Park. New Delhi 1 I0 017, India.
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`Printed in India at Shree Maitrey Printech Pvt. Ltd.. Noida
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`UTC-2024.002
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`UTC-2024.002
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`6.2 SUBSONIC INLETS
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`area to inlet area. The internal pressure rise depends on the reduction of velocity
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`between entry to the inlet diffuser and entry to the compressor (or burner, for
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`a ramjet). Nacelle size required for low drag can be quite strongly dependent on
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`the degree of external deceleration. In realistic analyses one must consider com-
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`pressibility effects.
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`Inlet Performance Criterion
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`As Chapter 5 showed, one may characterize the differences between actual
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`and ideal performance of aircraft engine inlets by a “diffuser efficiency” or by a
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`stagnation pressure ratio. We define these as follows:
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`a. Isentropic efficiency. Referring to Fig. 6.5, we can define the isentropic
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`efficiency of a diffuser in this form:
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`71:1:
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`h(J2s _ ha ~ T02: _ Tu
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`hfla _ ha
`T0a _ Ta .
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`State
`is defined as the state that would be reached by isentropic compression
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`to the actual outlet stagnation pressure. Since
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`T025 = I2 (771)/7
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`pa
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`and T2 =1 + y — 1M2,
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`Ta
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`the diffuser efficiency 71,; is also given by
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`(P02/pa)(7‘1)/7 _ 1
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`[(7 ~ 1)/21M2
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`b. Stagnation pressure ratio, rd. The stagnation pressure ratio,
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`rd = P02/p0aa
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`6.4
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`(6-5)
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`UTC-2024.003
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`225
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`CHAPTER 6 AEROTHERMODYNAMICS OF INLETS, COMBUSTORS, AND NOZZLES
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`1.00 0.95 0.90
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`0.850
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`0.6
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`FIGURE 6.6 Typical subsonic diffuser performance; 7 = 1.4.
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`is widely used as a measure of diffuser performance. Diffuser efficiency and stag-
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`nation pressure ratio are, of course, related. In general,
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`P041
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`P041
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`2
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`(66)
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`pa
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`and, with Eqs. (6.4) and (6.5),
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`pa
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`& = 22 . P_o« = _m(1+ 7 -1M2)”"“’,
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`(1 + ‘Y ‘ 1M2)(rd)(-y'1)/7 _ 1
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`2
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`[(7 — 1)/2lM2
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`Because 1),, will be primarily affected by the internal deceleration (“diffusion”),
`it is unfortunate that these criteria are based on overall deceleration rather than
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`on internal deceleration. The relationship between internal and external decel-
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`eration depends on engine mass flow rate as well as flight Mach number M. But
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`for illustrative purposes Fig. 6.6 gives typical values of stagnation pressure ratio
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`rd. The diffuser efficiency 1),, was calculated from rd, with the use of Eq. (6.6).
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`6.3 SUPERSONIC INLETS
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`Even for supersonic flight it remains necessary, at least for present designs,
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`that the flow leaving the inlet system be subsonic. Compressors capable of ingest-
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`ing a supersonic airstream could provide very high mass flow per unit area and,
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`theoretically at least, very high pressure ratio per stage. However, the difficulty of
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`passing a fully supersonic stream through the compressor without excessive shock
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`losses (especially at off-design conditions) has so far made the development of
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`fully supersonic compressors a possibility that is somewhat remote. As we will
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`see in Chapter 8, the Mach number of the axial flow approaching a subsonic
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