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1、J.FluidMech.(1987),vol.177,pp.233-246233PrintedinGreatBritainSteadyentryflowinacurvedpipeByP.H.M.BOVENDEERD,A.A.VANSTEENHOVEN,F.N.VANDEVOSSEANDG.VOSSERSDepartmentsofMechanicalEngineeringandPhysics,EindhovenUniversityofTechnology,TheNetherlands(Received28January19
2、86andinrevisedform12June1986)Laser-Dopplervelocitymeasurementswereperformedontheentryflowina90"bendofcircularcross-sectionwithacurvatureratioa/R=1/6.Thesteadyentryvelocityprofilewasparabolic,havingaReynoldsnumberRe=700,withacorrespondingDeannumberK=286.Bothaxiala
3、ndsecondaryvelocitiesweremeasured,enablingadetaileddescriptionofthecompleteflowfield.Thesecondaryflowattheentranceofthebendwasmeasuredtobedirectedcompletelytowardstheinnerbend.Significantdisturbanceoftheaxialvelocityfieldwasnotmeasureduntiladown-streamdistance(&)
4、$.Maximumsecondaryvelocitiesweremeasuredat1.7(aR)tdownstreamfromtheinlet.Thedevelopmentoftheaxialflowfieldcanbequitewellexplainedfromthesecondaryvelocityfield.1.IntroductionDetailedanalysisofthedevelopingfluidflowinbendshasbeenstronglystimulatedbyimprovednumerica
5、landexperimentalmethods.Moreoverthesubjectisrelevantfortheunderstandingofbloodflowinthehumanarterialsystem.ArecentoverviewoftheresultsofpreviousinvestigationsconcerningthestationaryentryflowinabendhasbeengivenbySohCBerger(1984).Theoreticalstudieshavebeenperformed
6、byHawthorne(1951)andSmith(1976).NumericalinvestigationshavebeencarriedoutbySingh(1974),Yao&Berger(1975),Stewartson,Cebeci&Chang(1980)andSoh&Berger(1984).ExperimentalanalysesweremadebyOlson(1971),Agrawel,Talbot&Gong(1978),Choi,Talbot&Cornet(1979)andOlson&Snyder(19
7、85).Mostoftheseinvestigationsdealwithuniformentryflowwhere,immediatelyaftertheentryintothebend,asecondaryflowissetup,whichisdominatedbythebuild-upofanaxialboundarylayer.Furtherdownstreamtwohelicalvorticesdevelopasaresultoftheinteractionofinertial,centrifugalandvi
8、scousforces.ThecaseofthedevelopmentfromaparabolicentryvelocityprofileinasituationofrelativehighcurvaturehasbeenstudiedbyOlson(1971).Hepresentedonlythedevelopme
