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1、ExperimentsinFluids12,2940(1991)ExperimentshFluids9Springer-Verlag1991Visualizationandimageprocessingofanacousticallyexcitedjetflow*Y.C.Chao**,M.S.JengandJ.M.HanInstituteofAeronauticsandAstronautics,NationalChengKungUniversity,Tainan,Taiwan,70101,R.O.C.Ab
2、stract.Recentworkinvestigatingexcitationeffectsonanacousti-tionlevelisraisedhighenough,specificforced-flowstruc-callyexcitedjetflowisreported.Emphasisisplacedonintegratedturesotherthanthewell-knownnaturalcharacteristics,be-visualizationandhigh-resolutionan
3、ddigitalimageprocessing,se-comedominant.Thesestructuresandtheirvorticalevolu-quentialplanargasconcentrationsandsomecharacteristicsofthelarge-scalevorticalstructuresofacousticallyexcitedjetflow,suchastionalcharacteristicsarelessknownandareofcurrentim-multip
4、le-eddymerging,vortex-braidsformation,eddyevolutionandportancetoresearchonmanipulatingturbulentflow.entrainmentprocesses,jet-boundaryexpansion,etc.Thedigitalim-Conventionally,probemeasurementssupplementedbyageprocessingtechniqueemployedhereextendsourprevio
5、usworkflow-visualizationtechniqueshavebeenusedtoanalyzetur-(Chaoetal.1990)tooptimalthresholdfilteringofthebackgroundnoiseandinsitucalibrationofcameraandilluminationdistortions.bulent-flowcharacteristics.FlowvisualizationisusedtoAcompact,low-cost,automaticf
6、rameacquisitionandanalysissys-makethecrucialconnectionofthecoherentstructurestothetemisdevelopedformeanandr.m.s,planargasconcentrationsandFourierspectralresultsoftheprobemeasurements.Inaddi-automaticjet-boundaryidentification.Also,stroboscopicimagestiontot
7、heaveragepropertiesacquiredwithpointwiseprobearecreatedfordetailedsequentialstudyofaquick-changingprocessdataandthequalitativeglobal-flowvisualizationimpres-usingalowframing-ratecamerabysuitablycontrollingtheacousticexcitationfrequencyandthejetflow.sion,Mi
8、escatteringanddigitalimage-processingtechniqueshaveproveduseful(e.g.Rosensweigetal.,1961;Becker,1977;Longetal.,1979,1981a,1981b,1983;Balintetal.,1985;VranosandLiscinsky,1986;Winteretal.,1987;Chao1Introduction
