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1、PROCESSINGTIMESERIESDATA(VELOCITY,SHEARSTRESS)FROMTHEPULSEWIDTHMODULATED-CONSTANTTEMPERATUREANEMOMETER(PWM-CTA)J.F.Foss,ProfessorMichiganStateUniversityMechanicalEngineeringDepartmentEastLansing,MI48824T.J.Hicks,ChiefEngineerDigitalFlowTechnologies,Inc.4731NakomaDriveOkemos,MI48864ABSTRAC
2、TThedigitaloutputfromthePWM-CTArepresentstheshortduration(e.g.,20msec)truetimeaverageoftheanalogvelocity(addressedherein)orshearstress.Thedevelopedtechniquestoextractthemomentsofthevelocity(orshearstress)distributionandtocreatearegulartimeseriesarepresentedinthispaper.INTRODUCTIONTheconst
3、anttemperatureanemometer(CTA)hasbeenanimportantinstrumentforfluidmechanicsresearchsinceitswidespreadavailabilityinthe1960s.TheuseoftheWheatstonebridgeandthefeedbackamplifier–whosedifferentialinputsignalsanincrease/decreaseincurrenttocompensateforamomentaryincrease/decreaseinthecoolingvelo
4、cityattheprobe–providesaservosystemthatiscapableoffollowingrapidfluctuationsofthevelocity.TheCTAhasbeenthesubjectofnumeroustechnicaldescriptions.RecommendedonesincludePerry1,Comte-Bellot2,FingersonandFreymuth3.ThePulseWidthModulated-ConstantTemperatureAnemometer(PWM-CTA)providesadistinctl
5、ydifferentelectronicarchitecture(incomparisonwiththeconventional(C)-CTA)withwhichtotrackhighfrequencyvelocityfluctuations.ThePWM-CTAwasintroducedinthepublicationbyFoss,etal.4andprotectedbythesubsequentlyissuedpatent:Hicks,etal.5.ThePWM-CTAhasbeenundercontinuousdevelopmentsincetheseearlydi
6、sclosureswiththemostrecentdescriptionprovidedbyFoss,etal.6inwhichcomparativemeasurements–withaDisa55Msystem–inaslit-jetflowfieldwerereported.Strongagreement,intermsofthefirstfourmomentsofthevelocitydistributionaswellasspectra,wereshowninthesecomparativemeasurements.Thepresentpaperisto:i)f
7、urtherclarifytheextractionofmomentsofthevelocity(orshearstress)distributionfromthePWM-CTAoutput,andii)toreportontheregularizingstrategythatisemployedtodevelopaperiodicoutputforsingleandmultiplesensormeasurements.Asshownbelow,thistransformationofthedataisrequiredsinc
