1IntroductionIn1931SirFrankWhittlepatentedtheselfsustainingGasTurbineEngine.Itconsistsofasinglerotatingspoolcomprisingacompressorandturbine（Fig.7.1）.Theengineisstartedbyspinningthecompressor.Thisestablishesarearwardflowofairintothecombustionzonewherefuelisaddedandignited.Thegassesincreaseintemperatureandthereforeexpandrearwards.Beforethegasesreachtheexhaustnozzle,someoftheirenergyisextractedbyrotatingtheturbine,whichinturndrivesthecompressor.Toincreasethethrustofthegasturbineengine,morefuelisaddedwhichraisestheenergylevelofthegasstream.下一頁返回1IntroductionTheturbinewillthereforebeturnedatagreaterspeedwhichwillturncompressoratagreaterspeed.Thecompressorwillthereforedeliveragreatermassofair,andthethrustforceofthegasturbineengineisthereforeincreasedaccordingtoNewton’s2ndLaw.Thethrustproducedbytheturbojetisproportionaltothechangeinmomentumofthegasstream.Toincreasethethrust,morefuelisintroducedwhichraisestheenergylevelofthegasstreamandtheturbineandcompressorrotateatahigherspeed.上一頁下一頁返回1IntroductionThecompressordeliversalargermassofairtothecombustionzoneandthereisacorrespondingincreaseinthethrustproducedbytheengine.Thegasturbinecanalsobecomparedwiththepistonenginewherefuelandairareburnedinsideacylindertocauseapistontomoveandturnacrankshaft.Theworkingcycleofthegasturbineengineisindeedsimilartothatofthe4-strokepistonengineasineachgasturbineenginethereisinduction,compression,combustionandexhaust.Inthepistonenginecyclethecombustioncycleisintermittentwhereasinthegasturbineengineitiscontinuous.上一頁下一頁返回1IntroductionThegasturbineenginehasaseparatecompressor,combustionchamber,turbinewheel,andexhaustsystemwitheachpartconcernedonlywithitsfunction.Thusthecombustioninagasturbineenginetakesplaceasacontinuousprocessataconstantpressure.This,combinedwiththeabsenceofreciprocatingparts,providesamuchsmootherrunningenginethatcanbeofalighterstructure,enablingmoreenergytobereleasedforusefulpropulsivework.Themoderngasturbineengineisbasicallycylindricalinshapebecauseitisessentiallyaductinwhichamassairflowisthesamefromtheintaketotheexhaustnozzle.Intothisductthenecessarypartsarefitted.上一頁下一頁返回1IntroductionThepartsfromfronttorearareanaircompressor,acombustionchamber,aturbinewheel,andanexhaustduct.Ashaftconnectstheturbinewheeltothecompressor,sothatturningtheturbinewillalsoturnthecompressor.Insidethecombustionchambersarefuelburnersandthemeansofignitingthefuel.Becausethejetengineisbasicallyanopenendedduct,itisnotsatisfactorytoignitethefuelinstaticair,becausethiswouldallowthegastoexpandequallyforwardsandbackwardswithoutdoinganyusefulwork;whentheairwasusedup,theflamewoulddieout.上一頁下一頁返回1IntroductionBeforelightingthefuelitis,therefore,essentialthattheairbemoving,andthemovingcolumnsofairmustbemovingthroughtheenginefromthefronttowardstherear.Thismovementisbroughtaboutbyusingastartermotortospinthecompressorandtheturbinewheelinexcessof1,500rpm;thisdrivesalargevolumeofairthroughthecombustionchamber.Whentheairflowissufficient,fuelisinjectedintothechambersthroughspraynozzles,andisignitedbymeansofigniterplugs（Notethatthegasturbineengineisnotanalternatefiringengine.上一頁下一頁返回1IntroductionThesparkignitersareonlyusedfortheinitialfiringandthefuelinallthecombustionchambersburnscontinuouslylikeablowtorch).Thisburningwillcausetheairflowtowardsthereartoincreaseinvelocityanddrivetheturbinewheelasitflowsovertheturbinebladesinitsheadlongrushthroughtheexhaustsystemouttoatmosphere.Thespinningturbinewheelturnsthecompressorthroughthedriveshaft,andthecompressorfeedsmoreairintothecombustionchambertocompleteacycleofoperationsthatcontinuesaslongasfuelisfedtotheburners.上一頁下一頁返回1IntroductionTheturbinewheelalsooriginatesadrivetoagearboxthatprovidesexternaldrivesforitemssuchasfuelpumps,hydraulicpumps,electricalgenerators,andotherengineaccessories.上一頁返回2ConstructionalArrangementsThebasicdesignofWhittlesgasturbineengineexistsinallgasturbineengines.Howevervariousapplicationshavebeenderivedoverthepast60yearstosuittheairframeandindustrialrequirements.2.1SingleSpoolAxialFlowEnginesAmodernsinglespoolaxialflowturbojetengine（Fig.7.2）producesitsthrustfromtheaccelerationoftheflowofthehotgases.Airenterstheengineinletandflowsintothecompressorwhereitspressureisincreased.Fuelisaddedinthecombustorwhereitisignitedandburns.下一頁返回2ConstructionalArrangementsExpandingthegasesastheyleavethetailpipeproducesthereactionweknowasthrust.Thesinglespoolturbojethasverylowpropulsiveefficiency,highspecificfuelconsumption（SFC）andanundesirablenoiselevel.Theuseofamultistageaxialflowcompressorenabledhighercompressionratiostobeobtainedandhencemorethrust.2.2Multi-spoolDesign上一頁下一頁返回2ConstructionalArrangementsDualandtriplespoolaxialcompressorsweredevelopedfortheoperationalflexibilitytheyprovidetotheengineintheformofhighcompressionratios,quickacceleration,andbettercontrolofstallcharacteristics.Thisoperationalflexibilityisnotpossiblewithsinglespoolaxialflowengines.Foranygivenpowerleversetting,thehighpressure（HP）compressorspeedisheldfairlyconstantbyafuelcontrolgovernor.Assumingthatafairlyconstantenergylevelisavailableattheturbine,thelowpressure（LP）compressorwillspeedupandslowdownwithchangesinaircraftinletconditionsresultinginchangesinatmosphericchangesormaneuversinflight.上一頁下一頁返回2ConstructionalArrangementsThevaryingLPcompressoroutputtherefore,providestheHPcompressorwiththebestinletconditionwithinthelimitsofthedesign.Thatis,theLPcompressortriestosupplytheHPcompressorwithafairlyconstantairpressureforaparticularairpressureforaparticularpowersetting.Tobetterunderstandwhenthelowpressurecompressorspeedsupandslowsdown,considerthatwhenambienttemperatureincreases,theair’smolecularmotionincreases.Inordertocollectairmoleculesatthesamerateastemperatureincreases,thecompressorwouldhavetochangeeitheritsbladeangles,whichitcannotdo,oritsspeed,whichitinfactdoes.上一頁下一頁返回2ConstructionalArrangementsAtwinspoolaxialflowengineisshowninFig.7.3.2.3BypassEngines2.3.1TwinSpoolLowBypassTurboFansThistypeofengine（Fig.7.4）hasatwinspoollayoutwiththeadditionthattheL.P.compressorisoflargerdiameterthanbeforeandthushandlesagreatermassofairthanisrequiredbytheH.P.compressor.TheairflowwhichisnotrequiredbytheH.P.compressorisfedintothebypassductanditrejoinsthenormalgasflowbehindtheturbines.上一頁下一頁返回2ConstructionalArrangementsTheairflowissplitapproximately50%eachway.Themixingofthe“hot”and“cold”gasstreamspromotesveryrapidexpansionofthegasses,whichgivesgoodpoweroutputwithalowfuelconsumption.Lowbypassenginesaredefinedashavingabypassratioof3∶1orless.2.3.2HighByPassTurboFansThedifferenceinoperationbetweenapropellerandapurejetenginecanbesummarizedasfollows：Apropelleracceleratesalargequantityofairrearwardsatalowrate.上一頁下一頁返回2ConstructionalArrangementsApurejetengineacceleratesasmallquantityofairrearwardsatahighrate.Thenetresultisthesame,buttheefficiencyofeachdependsontherequiredspeedoftheaircraft.Formediumspeedaircraft,acombinationofthetwohasbeendeveloped.Onthefollowingpagesaretwoexamplesofhighbypassmulti-spoolengines.Highbypassisdefinedasabypassratioof4∶1upto8∶1.Ultrahighbypassenginesarebeingresearchedwithabypassratioof10∶1andabove.上一頁下一頁返回2ConstructionalArrangementsAhighbypassengineismoreefficientthanapureturbojetbecauseitsprincipleofoperationismoreakintothatofapropeller,inthatitacceleratesarelativelylargemassofairatalowrate.2.3.3TwinSpoolHighBypasses（Fig.7.5,Fig.7.6）Theamountofairgoingthroughtheby-passsection（or“fan”）istypically5or6timesthatgoingthroughthecombustionsection.Approximately80%ofthethrustproducedisfromtheby-passairducting.上一頁下一頁返回2ConstructionalArrangements2.4TurboPropEnginesTheadventofthetwinspoolengineenabledeasierstarting（onlythesmallHPcompressorneedstoberotatedbythestarter）andbettersurgeresistanceasthetwospoolsrunattheirownoptimumspeeds.Thistypewasusedasapurethrustengine,buttheexampleshown（

Fig.7.7）droveapropellerontheendoftheLPcompressorshaftviaareductiongear.Alltypesinvariablyuseamulti-stageturbineandanepicyclicalreductiongear.上一頁下一頁返回2ConstructionalArrangementsThemultistageturbineswithsmalldiameterdiscscanrunatahigherrev/minandthusabsorbmoreenergyfromthegasstreamthanasinglelargediscthatmustnecessarilyberestrictedinrev/minbecauseofhighcentrifugalloading.Epicyclicalgearingisselectedforthereductiongearbecause：①Ahighdegreeofspeedreductioncanbeobtained.②Thepropellershaftandthrustlinesremainonthesamecenterlineasthecompressorandturbineshafts,thuscausinglittleinterferencewiththeentryofairintotheairintake.Streamliningofthewholeunitis,therefore,aneasiertask.上一頁下一頁返回2ConstructionalArrangementsThistypeofgasturbineengineisusedwhereverthedirectthrustfromtheengineisnotrequired.AlltheenergyinthegassesisabsorbedbytheturbinesandtransformedintoarotationalforceorTORQUE.Thereisusuallylittleornothrustproducedintheexhaust.ThereductiongearboxisrequiredbecausethegasturbineengineismostefficientathighRPM,butthedevicewhichitdrives（thepropeller,helicopterrotor,etc.）becomesinefficientatsuchahighspeed.上一頁下一頁返回2ConstructionalArrangementsThisexampleofaturbopropengine（Fig.7.8）usestwocentrifugalcompressorsintandem.Theyaredriven,alongwiththereductiongearbyathree-stageturbine,allononeshaft.Comparedwiththeaxialflowtwinspoolturbopropshownabovethisengineproducesmuchlesspowerandisveryinefficient.2.5TurboshaftEnginesAturboshaftengineisusedtodriveanyindustrialapplicationthatrequireshightorqueoutput.Forexample：上一頁下一頁返回2ConstructionalArrangements●Helicopterrotors●ShipDriveshafts●Hovercraftengines●Oilpumps●GeneratorsetsThisexampleusesafreeorpowerturbine(Fig.7.9).Alltheenergynotrequiredtodrivethegasgeneratorcompressorisusedtodrivethefreeturbinewhichdrivestheoutputshaft.上一頁下一頁返回2ConstructionalArrangementsTheoutputshaftisshownabovecomingoutofthefrontoftheenginebutitcanbegearedtocomeoutatanyangle,eventhroughtheexhaustdirectlyconnectedtotherearoftheturbine,takingthehelicopterturboshaftengineshowninFig.7.10asanexample.2.6TheCFM56-5TURBINGeneralIntroductiontotheengine：TheCFM56-5turbine—theannularcombustionchamberengine—isahighbypassratioturbofan.上一頁下一頁返回2ConstructionalArrangementsThisengineconsistsoffourparts：thelowpressurecompressor,high-pressurecompressor,combustionchamberandaccessorygearbox.Thelow-speedrotorconsistsofafrontfanandafour-stageLPconnectedtoafour-stageLPturbine.Thehighspeedrotorconsistsofanine-stageHPcompressorconnectedtoasingle-stageHPturbine.Theannularcombustionchamberisfittedwith20fuelnozzlesand2igniters.Theaccessorygearbox,locatedatthebottomofthefancase,receivestorquefromhorizontalHProtordriveshaftanddrivesgearboxmountedaccessories.上一頁下一頁返回2ConstructionalArrangementsEachpowerplanthasanFADEC（fullauthoritydigitalenginecontrol）system.FADECisadigitalcontrolsystemthatperformscompleteenginemanagement.FADEChastwo-channelredundancy,withonechannelactiveandtheotherinstandby.Ifonechannelfails,theotherautomaticallytakescontrol.2.7GeneralDescriptionofENGINECFM56-7TheCFM56-7isahighbypass,dualrotor,axialflowturbofanengine.Theenginefandiameteris61inches.上一頁下一頁返回2ConstructionalArrangementsThebareengineweightis5,257pounds.Theenginehasthesesections：thefanandbooster,high-pressurecompressor（HPC）;combustor;high-pressureturbine（HPT）;low-pressureturbine（LPT）;accessorydrive.Thefanandboosterisafour-stagecompressor.Thefanincreasesthespeedoftheair.Asplitterfairingdividestheairintothesetwoairflows：primaryandsecondary.Theprimaryairflowgoesintothecoreoftheengine.TheboosterincreasesthepressureofthisairandsendsittotheHPC.Thesecondaryairflowgoesinthefanduct.Itsuppliesapproximately80percentofthethrustduringtake-off.上一頁下一頁返回2ConstructionalArrangementsTheHPCisanine-stagecompressor.ItincreasesthepressureoftheairfromtheLPCandsendsittothecombustor.TheHPCalsosuppliesbleedairfortheaircraftpneumaticsystemandtheengineairsystem.Thecombustormixesairfromthecompressorsandfuelfromthefuelnozzles.Themixtureofairandfuelburnsinthecombustionchambertomakehotgases.ThehotgasesgototheHPT.TheHPTisasingle-stageturbine.Itchangestheenergyofthehotgasesintoamechanicalenergy.上一頁下一頁返回2ConstructionalArrangementsTheHPTusesthismechanicalenergytoturnontheHPCrotorandtheaccessorydrive.TheLPTisafour-stageturbine.Itchangestheenergyofthehotgasesintomechanicalenergy.TheLPTusesthismechanicalenergytoturnthefanandboosterrotor.2.8EngineOilSystemTheengineoilsystemhasthesesubsystem,storage,distribution,indicatingandstorage.上一頁下一頁返回2ConstructionalArrangementsTheactuatorsaslightmist-riggingintheflaptransmissionhadbeeninduced.Thiswasfoundasacontributingfactorinthereportedflaplocks.Flaprotaryactuatorsfilledwithgreasepre-mod28898orpre-mod28899needremovalforregreasingapproximatelyevery5years（refertoMPDtask275449-05-1）.Anewtypeofactuatorpostmod28898or28899（postSB27-1138）embodiedsinceMSN1256isfilledwithsemifluidandisserviceableonthewing.Thiseasesmaintenanceandavoidstheremoval/installationoftheactuators.上一頁下一頁返回2ConstructionalArrangementsTheoilstoragesystemkeepssufficientoilforacontinuoussupplytotheoildistributioncircuit.Theoilstoragesystemletsyoudoanoillevelcheckandtofilltheoilsystem.Theoilstoragesystemholdsoilintheoiltank.Theoildistributionsystemhasthesecircuits,supply,scavengeandvent.Thesupplycircuitsendsoiltolubricatetheenginebearingsandgears.Theoilfromthetankgoestothelubricationunitthroughananti-leakagevalve.Thelubricationunitpressurizesandfilterstheoil.Theoilthengoestotheengine.上一頁下一頁返回2ConstructionalArrangementsThescavengecircuittakestheoilfromtheengine.Oilfirstflowsthroughthelubricationunit.Thelubricationunitalsoscavengestheoil.Theoilgoestothescavengeoilfilterandthentotheservofuelheater.Theoilgoesfromtheservofuelheatertothemainfuelheatexchangerandtotheoiltank.Theventcir