6 compressible high speed gas flow外语英文电子书

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1、Compressiblehigh-speedgasflow6.1IntroductionProblemsposedbyhigh-speedgasflowareofobviouspracticalimportance.Applica-tionsrangefromtheexteriorflowsassociatedwithflighttointeriorflowstypicalofturbomachinery.Asthecostofphysicalexperimentsishigh,thepossibiliti

2、esofcomputationswereexploredearlyandthedevelopmentconcentratedontheuseoffinitedifferenceandassociatedfinitevolumemethods.Itwasonlyinthe1980sthatthepotentialofferedbythefiniteelementformswererealizedandthefieldisexpandingrapidly.Oneofthemainadvantagesintheu

3、seofthefiniteelementapproximationhereisitscapabilityoffittingcomplexformsandpermittinglocalrefinementwhererequired.However,theimprovedapproximationisalsoofsubstantialimportanceaspracticalproblemswillofteninvolvethree-dimensionaldiscretizationwiththenumbero

4、fdegreesoffreedommuchlargerthanthoseencounteredintypicalstructuralproblems(105-107DOFareherequitetypical).Forsuchlargeproblemsdirectsolutionmethodsareobviouslynotpracticableanditerativemethodsbasedgenerallyontransientcomputationformsareinvariablyused.Hereo

5、fcoursewefollowandacceptmuchthathasbeenestablishedbythefinitedifferenceapplicationsbutgenerallywilllosesomecomputationalefficiencyassociatedwithstructuredmeshestypicallyusedhere.However,thereductionoftheproblemsizewhich,asweshallsee,canbeobtainedbylocalref

6、inementandadaptivitywillmorethancompensateforthisloss(thoughofcoursestructuredmeshesareincludedinthefiniteelementforms).InChapters1and3wehaveintroducedthebasicequationsgoverningtheflowofcompressiblegasesaswellasofincompressiblefluids.Indeedinthelatter,asin

7、Chapter4,wecanintroducesmallamountsofcompressibilityintotheproceduresdevelopedtherespecificallyforincompressibleflow.Hereweshalldealwithhigh-speedflowswithMachnumbersgenerallyinexcessof0.5.Suchflowswillusuallyinvolvetheformationofshockswithcharacteristicdi

8、scontinuities.Forthisreasonweshallconcentrateontheuseoflow-orderelementsandofexplicitmethods,suchasthoseintroducedinChapters2and3.Herethepioneeringworkofthefirstauthor'scolleaguesMorgan,LohnerandPerairemustbe