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1、PARTIEngineCycleDesign1TheDesignProcess1,1IntroductionThisisatextbookondesign.Wehaveattemptedtocapturetheessenceofthedesignprocessbymeansofarealisticandcompletedesignexperience.Indoingthis,wehavehadtobridgethegapbetweentraditionalacademictextbooks,whichemphasizeindividualconceptsandprincip
2、les,anddesignhandbooks,whichpro-videcollectionsofknownsolutions.Themostchallengingandproductiveactivitiesofthenormalengineeringcareerareatneitherendofthespectrum,but,instead,re-quirethesimultaneousapplicationofmanyprinciplesforthesolutionofaltogethernewproblems.Thevehicleemployedinordertoa
3、ccomplishourteachinggoalsistheairbreath-inggasturbineengine.Thismarvelousmachineisapillarofourmoderntechno-logicalsocietyandcomesinmanyfamiliarforms,suchastheturbojet,turbofan,turboprop,andafterburningturbojet.Withsuchavarietyofengineconfigurations,themostappropriateforagivenapplicationcan
4、notbedeterminedwithoutgoingthroughthedesignprocess.1.2DesigningIsDifferentItshouldbemadeclearattheoutsetwhatisspecialaboutthedesignprocess,forthatiswhatthistextbookwillattempttoemphasize.Everydesignerhasanimageofwhatelementsconstitutethedesignprocess,andsoourversionisnotlikelytobeexhaustiv
5、e.Nevertheless,thefollowinglistcontainscriticalelementswithwhichfewwoulddisagree:1)Thedesignprocessisbothstartedbyandconstrainedbyanidentifiedneed.2)Inthecaseofthedesignofsystems,suchasaircraftandengines,manylegitimatesolutionsoftenexist,andnonecanbeidentifiedasuniqueoroptimum.Systematicme
6、thodsmustbefoundtoidentifythemostpreferredor"best"solu-tions.Thefinalselectionalwaysinvolvesjudgmentandcompromise.3)Theprocessisinherentlyiterative,oftenrequiringthereturntoanearlierstepwhenpriorassumptionsarefoundtobeinvalid.4)Manytechnicalspecialtiesareinterwoven.Forexample,gasturbineeng
7、inedesigninvolvesatleastthermodynamics,aerodynamics,heattransfer,combustion,structures,materials,manufacturingprocesses,instrumentation,andcontrols.5)Aboveall,thedesignofacomplexsystemrequiresactiveparticipationanddisciplinedcommunicationbyeveryoneinvolved.Bec
