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1、VortexsoundduetoaflexibleboundarybackedbyacavityinalowMachnumbermeanflowaS.K.TangDepartmentofBuildingServicesEngineering,TheHongKongPolytechnicUniversity,HongKong,ChinaR.C.K.LeungandR.M.C.SoDepartmentofMechanicalEngineering,TheHongKongPolytechnicUniversity,HongKong,ChinaReceived26Apr
2、il2006;revised5November2006;accepted15December2006Lowfrequencysoundradiatedduetotheunsteadymotionofaninviscidvortexintheproximityofaßexiblemembranebackedbyanairtightcavityonanotherwiserigidplaneisinvestigatedtheoretically.Resultsshowthatbothmonopoleanddipolearecreatedbutthelatterisi
3、mportantonlywhenthevortexistraversingoverthemembrane.Themonopoleresultsfromthemembranevibrationandthedipolefromthetransversemotionofthevortex.ItisalsofoundthatthesesoundÞeldstendtocounteracteachother.Theincreaseinthemeanßowspeedingeneralresultsinastrongeracousticpowerradiation,butsou
4、ndattenuationmaybepossibleifthemembrane-cavitysystemisweakcomparedwiththemeanßowmomentum.©2007AcousticalSocietyofAmerica.DOI:10.1121/1.2434240PACSnumbers:43.28.Ra,43.40.Rj,43.50.NmGCLPages:1345Ð1352I.INTRODUCTIONcomputationoftheacousticÞeld,theßowÞeld,andtheßow-inducedvibration
5、oftheßexibleboundary.TherehaveItiswellknownthattheunsteadymotionofturbulencebeenstudiesconcerningthenoiseradiatedfromplatevibra-isanimportantsourceofaerodynamicsound,especiallyintiondrivenbyaturbulentßowbyassumingacertainturbu-thepresenceofnonrigidsolidsurfaces.1,2Theregeneration1112
6、lencespectrumforinstance,Davies,WuandMaestrello,noiseinsideandthebreakoutnoisefromanairductina13andDowell.However,suchassumptiontendstoignorethebuildingconveyinglowMachnumberturbulentßowareimportantcouplingamongtheßow,theacousticÞeld,and3typicalexamplesofsuchsound.Silencingdevices,
7、suchastheplate.Also,theunderlyingsoundgenerationmechanisms4thedissipativesilencerandexpansionchamber,whicharehavenotbeendiscussed.adoptedtoattenuatefannoiseintheventilationsystemwillRealturbulenceisalsodifÞculttohandletheoretically,alsointeractwiththeturbulentßowtoproducenoise.Thisma
8、kingthestudy
