Theory of Aerospace Propulsion PDF
Preview Theory of Aerospace Propulsion
Theory of Aerospace Propulsion Theory of Aerospace Propulsion Second Edition Pasquale M. Sforza University ofFlorida AMSTERDAM (cid:129) BOSTON (cid:129) HEIDELBERG (cid:129) LONDON NEW YORK (cid:129) OXFORD (cid:129) PARIS (cid:129) SAN DIEGO SAN FRANCISCO (cid:129) SINGAPORE (cid:129) SYDNEY (cid:129) TOKYO Butterworth-Heinemann is an imprint of Elsevier Butterworth-HeinemannisanimprintofElsevier TheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UnitedKingdom 50HampshireStreet,5thFloor,Cambridge,MA02139,UnitedStates Copyright#2017,2012ElsevierInc.Allrightsreserved. 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LibraryofCongressCataloging-in-PublicationData AcatalogrecordforthisbookisavailablefromtheLibraryofCongress BritishLibraryCataloguing-in-PublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary ISBN:978-0-12-809326-9 ForinformationonallButterworth-Heinemannpublications visitourwebsiteathttps://www.elsevier.com/ Publisher:ToddGreen AcquisitionEditor:SteveMerken EditorialProjectManager:NathanielMcFadden ProductionProjectManager:PunithavathyGovindaradjane CoverDesigner:MariaIn^esCruz TypesetbySPiGlobal,India Preface to the Second Edition This edition reflects updates of and emendations to the first edition, which originally derived from notes developed and assembled over many years of teaching propulsion and high-speed airplane andspacecraftdesigncoursesatthePolytechnicInstituteofBrooklyn(nowpartofNewYorkUniver- sity),aswellascoursesinpropulsionandaerospacevehicledesignattheUniversityofFlorida.The book remains aimed at presenting the theory and concepts of propulsion through a fundamental approachsuitableforcoursesattheseniorundergraduateandfirstyearmaster’slevel.Theexercises areintendedtopromoteanappreciationforapplicationsofthetheorytoproblemsofpracticalinterest. Generalchangestothefirsteditionincludetheadditionofanintroductorysectionatthestartofeach chapteraswellasasummarysectionconcludingeachchapter.Manyofthefiguresandgraphshave beenimproved,additionalexampleproblemshavebeenadded,andthenumberofexercisesincreased. Errors appearing inthe first edition have been tracked down and corrected. Chapter1,nowtitled“PropulsionPrinciplesandEngineClassification,”isaimedatintroducingthe readertothedifferenttypesofjetpropulsionenginesandprovidesaquantitativefoundationbasedon quasi-one-dimensional conservation equations. Airbreathing propulsion systems treated include pro- pellers, turbojets, turbofans, pulsejets, ramjets, and scramjets. The section on the turbofan has been rewrittenandsectionsonaerospacepropulsionfuelsandspacepropulsionengineshavebeenadded. Thesectiondealingwiththeconditionsforachievingmaximumthrusthasbeenexpandedandmovedto Chapter5, which deals withnozzles. Chapter2developsthequasi-one-dimensionalequationsthatenjoywideuseinthedesignandanal- ysisofvariouspropulsionsystems.Thesectionontheconservationofchemicalspeciesequationwas rewrittenandthesectionontheequationsofmotioninstandardformwasexpandedtoincludeclassical Fanno and Rayleigh flows. Chapter 3 carries out an extensive set of analyses of the operation of a variety of airbreathing enginesunderconditionsofidealoperationtomaintainafocusonunderlyingconcepts.Eightseparate casesarestudied:maximumpowertakeoffofturbojetsandturbofans,highsubsoniccruiseofturbojets andturbofans,supersoniccruiseofturbojets,turbofans,andramjets,andhypersoniccruiseofscram- jets. These detailed analyses offer the equivalent of a set of sample exercises to aid the reader in understanding the ideal workings of the various engines and flight regimes. A section on the effect of the efficiencies of the various components of real engines is presented in a manner that should facilitate repeating the calculation of all the cases with reasonable concern for the losses common topractical operation. Chapters4,5,and6eachconcentrateononeofthethreeenginecomponentsbasictojetpropulsion principles:combustors,nozzles,andinlets.Fundamentalsarediscussedinsomedetailandapplication toactualhardwareisshown.Chapter4dealswithcombustionchambersforairbreathingenginesand treatsconstantareaandconstantpressurecombustorsandincludesanewsectiononsupersoniccom- bustion.Thecalculationofchemicalequilibriumcompositionandadiabaticflametemperatureisde- scribed and a more comprehensive example problem for adiabatic flame temperature replaces the simpleroneinthepreviousedition.Chapter5isnowtitled“NozzlesforAirbreathingEngines”denot- ingitsparticularemphasis.Asectiononconditionsformaximumthrusthasbeenaddedandincludes theeffectsofstagnationtemperatureandbackpressureonthrust.Chapter6isnowcalled“Inletsfor xviii PREFACE TO THE SECOND EDITION xix Airbreathing Engines” and includes a section on inlets in subsonic flight which discusses inlet lip design,inletductfrictionlosses,andinletboundarylayerdiverters.Asectionontotalpressurerecovery with friction and shock wavelosseshas been added. ThenChapters7and8aredevotedtothefundamentalsoftheturbomachineryrequiredforoperating airbreathingjetenginesthroughouttheflightrangeuptoandincludingsupersonicspeeds.Chapter7 developsthegasdynamicsandthermodynamicsofturbomachineryneededforanalyzingcentrifugal flowcompressorsandaxialflowcompressorsandturbines,includingvelocitydiagramsandthedevel- opmentofperformancemapsfrombasicaerodynamicprinciples.Chapter8delvesdeeperintothede- tailsofflowswithinbladepassagesanddiscussestheimportantfactorsofboundarylayerseparationfor compressorsandheattransferforturbines.AnewsectiononcalculatingtheoptimumMachnumberat the compressor face hasbeen added. Integratingthevariouscomponentsdiscussedinthepreviousfivechaptersintoaworkingengineis the subject of Chapter 9. The description of different types of turbojet and turbofan engines now includesadiscussiononthegearedturbofanengine.Thesimilarityvariablesimportantinthematching process are derived and detailed matching analyses for two basic design approaches are presented. Issues concerning inlet-engine matching, thrust monitoring and control in flight, and fuel delivery systems are discussed. ThelastchapterconcernedwithaircraftflightoperationsisChapter10,whichcoverstheoperation ofpropellersandtheapplicationofthegasturbineenginetothem.Asectiondevotedtoasimpleanal- ysisfordeterminingstaticthrustandasectionongearedturbofansandopenrotorengineshavebeen added along with an extensiveexample problem on turboprop performance. Chapters 11 and 12 are concerned with liquid and solid propellant rocket engines, respectively, whileChapter13isdevotedtospacepropulsionsystems.Chapter11hasbeenexpandedandlargely rewrittenandasectiononpropellantdensityandspecificimpulsehasbeenadded.Thesectiononliquid propellantsnowincludesdetailedassessmentsoftheLH -LOX,RP1-LOX,andtheLCH /LOXpro- 2 4 pellantcombinations.Thesectiononliquidpropellanttankandfeedsystemdesignhasbeenupdated andrewrittenandnowincludesdiscussionofliquidpropellanttankcharacteristics,analysis,andstruc- tural design, as well as liquid propellant feed systems and turbopump analysis and sizing consider- ations. Chapter 12 deals with solid propellant rocket motors and includes a new section on solid propellant rocketmotor sizingand anassociated worked example. Chapter 13 covers the area of space propulsion with attention given to electric propulsion tech- niquesthatareofimportanceinsatelliteoperationsandspaceexplorationandnowincorporatesnuclear propulsion andits possiblerolein interplanetary missions. Theeightappendicesdealwithimportantauxiliaryinformationforthemaintext:AppendixApre- sents equations for the calculation of shock waves and expansions and includes tables and charts. Appendix B gives tables for the properties of hydrocarbon fuel combustion products and includes a narrative explaining the tables and their use. Appendix C gives a brief discussion of the physics of theearth’satmospherewithexpandedtablesofatmosphericpropertiesforgreaterutility.Thematerial inAppendicesDandEcoversboostphaseandstagingofrocketsandsafety,reliability,andriskas- sessmentusingmaterialfromtheauthor’sbookMannedSpacecraftDesignPrinciples(Elsevier,2015). AppendixFdealswithaircraftperformanceintakeoffandcruiseusingmaterialfromtheauthor’sbook CommercialAirplaneDesignPrinciples(Elsevier,2014).Tablesofthermodynamicpropertiesofse- lectedchemical speciesappropriatetopropulsionapplications arepresentedinAppendixGwhileH providesa listing of useful constants andconversion factors. xx PREFACE TO THE SECOND EDITION IwouldliketoagainacknowledgetheinspirationprovidedbyProfessorAntonioFerri,pioneerand championofscramjetdevelopment,whotaughtpropulsioncoursesItookasagraduatestudentatthe PolytechnicInstituteofBrooklynmanyyearsago.AppreciationisalsoduemyclosecolleaguesPro- fessorHerbertFoxoftheNewYorkInstituteofTechnologyandthelateProfessorMarianVisichofthe StateUniversityofNewYorkatStonyBrookfortheirlong-termcooperationin,criticismof,andsup- port for this book. Thanks are also due to a number of reviewers who have offered well-considered criticismofthefirsteditionandprovidedusefulsuggestionsandrecommendationswhichIhopeIhave used wisely inpreparingthis edition. Finally,and most importantly, Ithankmywife, Anne, who continues toencourage, support,and assist me in these writing projectsinspite ofthe time ittakesme awayfrom her company. Pasquale M.Sforza Professor of AerospaceEngineering, Emeritus [email protected] CHAPTER 1 PROPULSION PRINCIPLES AND ENGINE CLASSIFICATION CHAPTER OUTLINE 1.1 IntroductiontoAerospacePropulsionEngines ..................................................................................2 1.2 ConservationEquations ...................................................................................................................3 1.2.1 ConservationofMass ..................................................................................................4 1.2.2 ConservationofMomentum .........................................................................................4 1.2.3 ConservationofEnergy ................................................................................................5 1.3 FlowMachineswithNoHeatAddition:Propellers,Fans,Compressors,andTurbines ..........................5 1.3.1 ZeroHeatAdditionwithVe>V0 ...................................................................................7 1.3.2 ZeroHeatAdditionwithVe<V0 ...................................................................................7 1.3.3 ZeroHeatAdditionwithP¼Constant>0 ....................................................................7 1.3.4 PropulsiveEfficiency ..................................................................................................8 1.3.5 Example:PropellerSpeedandThrust ...........................................................................8 1.4 FlowMachineswithNoNetPowerAddition:Turbojets,Ramjets,Scramjets,andPulsejets ..............10 1.4.1 HeatAddition,Q>0 .................................................................................................10 1.4.2 ThrustVariationwithFlightSpeed..............................................................................13 1.4.3 OverallEfficiency .....................................................................................................13 1.4.4 FuelEfficiency .........................................................................................................14 1.4.5 Example:TurbojetSpecificFuelConsumption.............................................................18 1.5 FlowMachineswithP50,Q5ConstantandA 50:TheRocket ....................................................20 0 1.5.1 ThrustVariationwithFlightSpeed..............................................................................20 1.5.2 PropulsiveEfficiency ................................................................................................21 1.5.3 FuelEfficiencyandSpecificImpulse .........................................................................21 1.6 TheSpecialCaseofCombinedHeatandPower:TheTurbofan .......................................................23 1.6.1 VerySmallBypassRatio,β≪1,theTurbojet ..............................................................24 1.6.2 SmalltoLargeBypassRatio,β(cid:2)10,theTurbofan ......................................................25 1.6.3 Example:TurbofanSpecificFuelConsumption ............................................................26 1.6.4 VeryLargeBypassRatio,β≫1,theTurbopropandtheOpenRotor ...............................27 1.7 AerospacePropulsionFuels .........................................................................................................28 1.7.1 JetEngineFuels .......................................................................................................29 1.7.2 RocketEngineFuels .................................................................................................30 1.7.3 FuelEnergyContent..................................................................................................30 1 TheoryofAerospacePropulsion.http://dx.doi.org/10.1016/B978-0-12-809326-9.00001-4 Copyright#2017ElsevierInc.Allrightsreserved. 2 CHAPTER 1 PROPULSION PRINCIPLES AND ENGINE CLASSIFICATION 1.8 SpacePropulsionEngines ............................................................................................................31 1.8.1 HeatAdditionUsingNuclearorElectricPower ............................................................31 1.8.2 ElectrostaticAcceleration ..........................................................................................32 1.8.3 ElectromagneticAcceleration.....................................................................................32 1.9 TheForceFieldforAirbreathingEngines.......................................................................................33 1.9.1 Example:JetEnginePerformance ..............................................................................39 1.9.2 Example:RocketEnginePerformance ........................................................................41 1.10 Summary ....................................................................................................................................42 1.11 UsefulConstantsandConversionFactors ......................................................................................43 1.12 Nomenclature .............................................................................................................................43 1.12.1 Subscripts ............................................................................................................44 1.13 Exercises ....................................................................................................................................45 Reference ............................................................................................................................................52 1.1 INTRODUCTION TO AEROSPACE PROPULSION ENGINES The operation of aerospace propulsion engines rests on the foundation of Newton’s laws of motion. Thesecondoftheselawsexplainsthatthechangeinmomentumofthefluidpassingthroughanengine isequaltotheforceactingonthefluid.Thethirdlawstatesthattheforceactingonthefluidexertsa reaction, an equal andopposite force, on the boundaries separating the fluidand the engine. Indeed, such engines are oftenreferred toasreactionmotors. Ingeneral,aerospacepropulsionenginesmaybethoughtofasidealizedflowmachinesinwhich fluidwithin the machine haswork and/orheat added toitpriortoitsexitfrom themachine asajet, therebyproducingthrustaccordingtothereactionprincipledescribedabove.Thefluidmayenterthe machinefromthesurroundingsormaybecarriedentirelywithinthemachinepriortobeingprocessed. Theformerenginesareusuallycalledairbreathingenginesandthelatter,rockets.Ofprimaryinterestis themagnitudeofthethrustproducedandtheefficiencywithwhichtheheatandpowerisusedingen- eratingthrust.Inthischapterwewillclassifythedifferenttypesofaerospacepropulsionenginesand quantitativelydescribetheperformanceofeachbyapplyingthebasicintegralformsoftheconserva- tion equationsof gasdynamics. Themostefficientflowmachineisthepropeller,inwhichworkisdoneonthefluidpassingthrough it,butnoheatisadded.Thesourceofpowerisexternaltothepropelleritselfandmaybeaninternal combustion engine, a gas turbine, or even an electric motor. In this chapter we show that though efficient,thepropellerisspeed-limitedinthesensethatforagivenpowerinputthethrustdeveloped falls off with increasing speed. Conversely,theturbojet,ramjet,scramjet,andpulsejetareflowmachinesinwhichheatisaddedto the airstream taken aboard, but no net work is done on it. The heat is added by burning fuel in that airstream.Thethrusttheydevelophasarelativelyweakdependenceonflightspeedmakingthemca- pableofgoodperformanceatmuchhigherspeedsthanareachievablewithpropellers.However,they are less efficient than propellers and their ability to travel at higher, even supersonic, speeds is thus gainedatthecostofgreaterfuelconsumption.Therocket,avariantofthiscase,takesinnoambient 1.2 CONSERVATION EQUATIONS 3 fluidbut instead carries onboard all the fluidto which heat isadded, again by combustion,and sub- sequentlyejectedasajet.Thethrustoftherocketisindependentoftheflightspeedbutthisadvantage ispaidforbyevenlowerefficiencythantheotherjetengines.Ontheotherhand,becauseallthenec- essarypropellant iscarriedonboard the rocket isable tooperate inthe vacuum of space. Ratherthanaddpoweraloneorheatalonetotheworkingfluidweshowthatbyaddingacombi- nationofpowerandheatwecanderivesomeofthespecialbenefitsofboththepropellerandthetur- bojet.Thisistheturbofanenginewhichisthecommonjetpowerplantforbothcommercialandmilitary aircrafts. Forspaceapplicationsweexaminemeansotherthanchemicalcombustiontoenergizeanonboard propellant. Nuclear thermal propulsion (NTP) involves heating the onboard propellant by passing it through a nuclear fission reactor. Such rockets can provide high thrust with higher efficiency than a chemical rocket but pose radiation safety issues. Simple electrical resistance heating of a propellant isthebasisoftheresistojetwhilethearcjetusesanelectricdischargetoheatpropellant.Wealsoex- aminethehighlyefficientbutlowthrustionrocketwhichgeneratesthrustbyelectrostaticacceleration ofionsandthemagnetoplasmadynamic(MPD)rocketwhichuseselectromagneticaccelerationtoac- celerateelectricdischarge-producedplasma.TheionandMPDrocketsexhibitveryhighefficiencybut are limited torelativelylow thrust levels. After illustrating the different engine types which use the principle of jet propulsion, attentionis focusedondetailsoftheforcefieldgeneratedbysuchenginesandthefactorsinfluencingtheproduc- tion of thrust. 1.2 CONSERVATION EQUATIONS Aflowmachineisonewhichingestsastreamoffluid,processesitinternallyinsomefashion,andthen ejects the processed fluid back into the ambient surroundings. An idealization of such a generalized flowmachineisschematically depictedin Fig.1.1. r r 0 e p p 0 e V V 0 e A A 0 e 0 e FIG.1.1 Schematicdiagramofidealizedflowmachineandassociatedstreamtubecontrolvolume. Inordertodevelopthebasicfeaturesofoperationoftheidealizedflowmachinewithoutintroducing unnecessary algebraic complexity, we make the following assumptions: (cid:129) The flow through the streamtube entering and leaving the machine issteady and quasi-one- dimensional. Mass cannot cross the streamtubesurfaces. 4 CHAPTER 1 PROPULSION PRINCIPLES AND ENGINE CLASSIFICATION (cid:129) Theentranceandexitstationsshownarechosensufficientlyfarfromtheflowmachineentranceandexit suchthatthepressuresatthosestationsareinequilibriumwiththeirsurroundings,thatis,p ¼p . e 0 (cid:129) There isno heat transfer across the boundariesof the streamtube orthe flow machine into the ambient surroundings. (cid:129) Frictional forces on the entering and leaving streamtube surfacesare negligible. (cid:129) Massinjectedintoorextractedfromthefluidstreamwithintheflowmachine,ifany,isnegligible compared tothe massflowentering the flowmachine. With these restrictions in mind we may assess the consequences of applying the basic conservation principlestothestreamtubecontrolvolume.Amoredetaileddiscussionanddevelopmentofthecon- servation laws and associated thermodynamic principles is presented in Chapter 2. At this point we wishtousethesimplestformoftheselawstoclassifythewidevarietyofaerospacepropulsiondevices. However,therearesomeimplicationsoftheassumptionsusedwhichareimportanttokeepinmind. TheassumptionofsteadyflowimpliesthatV isconstant,thatis,theidealizedflowmachinemay 0 beconsideredtobeflyingatthespeedV throughastationaryatmospherewiththeambientenviron- 0 mentalvaluesofpressure,density,andtemperaturedenotedinFig.1.1byp ,ρ ,andT ,respectively. 0 0 0 Alternatively,wemayconsiderourcoordinatesystem tobefixedontheflowmachinesuch thatthe atmosphereconstitutesafreestreamflowapproachingatspeedV withstaticconditionsofpressure, 0 density,andtemperaturedenotedinFig.1.1byp ,ρ ,andT ,respectively.This(Galilean)transfor- 0 0 0 mation of coordinates ispossiblebecausethe motion issteady. Anotherimplicationarisingfromtheassumptionthattheflowmachineismovingthroughtheat- mosphereatconstantspeedisthattheremustbenounbalancedforceonthemachine.Sincetherewill be resistance to the motion arising from the aerodynamic drag D there must be another force acting which can balance it and so maintain the constant motion and that is the thrust F. The rate at which work must be done to maintain the motion is DV and because D¼F the required power may also 0 be written asFV . 0 1.2.1 CONSERVATION OF MASS Because mass can neither be created nor destroyed and any mass addition or subtraction within the flowmachineisassumednegligible,thenetchangeinthemassflowpassingthroughtheflowmachine is zero. The assumption of quasi-one-dimensional flow and assigning a negative sign to flow into the control volume and a positive sign to flow leaving the control volume permits us to write this balance as (cid:3)ρ A V +ρ A V ¼0 (1.1) 0 0 0 e e e Thisisequivalenttostatingthatthemassflowm_¼ρAV¼ constantthroughoutthesystem.Fordensity inkg/s,area in m2, and velocity inm/s the mass flow has the unitsof kg/s. 1.2.2 CONSERVATION OF MOMENTUM Newton’ssecondlawofmotionrequiresthatthenetchangeinmomentumofthefluidpassingthrough thestreamtubeisequaltotheforceactingonthefluid.Usingthesignconventionformassflowgiven by Eq. (1.1) the change inthe momentumofthe fluidisgiven by ð(cid:3)ρ A V ÞV +ðρ A V ÞV ¼F 0 0 0 0 e e e e
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