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1、NASA/CR-2001-211021ICASEReportNo.2001-19SeedlessLaserVelocimetryUsingHeterodyneLaser-inducedThermalAcousticsRogerC.HartICASE,Hampton,VirginiaR.JeffreyBalla,G.C.Herring,andLutherN.JenkinsNASALangleyResearchCenter,Hampton,VirginiaICASENASALangleyResearchCenterHampton,Vi
2、rginiaOperatedbyUniversitiesSpaceResearchAssociationNationalAeronauticsandSpaceAdministrationLangleyResearchCenterPreparedforLangleyResearchCenterHampton,Virginia23681-2199underContractNAS1-97046August2001SEEDLESSLASERVELOCIMETRYUSINGHETERODYNELASER-INDUCEDTHERMALACOU
3、STICS*†‡§ROGERC.HART,R.JEFFREYBALLA,G.C.HERRING,ANDLUTHERN.JENKINSAbstract.AneedexistsforaseedlessequivalentoflaserDopplervelocimetry(LDV)foruseinlow-turbulenceorsupersonicflowsorelsewherewhereseedingisundesirableorimpractical.Acompactlaservelocimeterusingheterodyneno
4、n-resonantlaser-inducedthermalacoustics(LITA)tomeasureasinglecomponentofvelocityisdescribed.Neithermolecular(e.g.NO2)norparticulateseedisaddedtotheflow.Innon-resonantLITAtwobeamssplitfromashort-pulsepumplaserarecrossed;interferenceproducestwocounterpropagatingsoundwav
5、esbyelectrostriction.ACWprobelaserincidentonthesoundwavesattheproperangleisdiffractedtowardsadetector.MeasurementofthebeatingbetweentheDoppler-shiftedlightandahighlyattenuatedportionoftheprobebeamallowsdeterminationofonecomponentofflowvelocity,speedofsound,andtemperat
6、ure.ThesoundwavesessentiallytaketheplaceoftheparticulateseedusedinLDV.Thevelocimeterwasusedtostudytheflowbehindarearward-facingstepinNASALangleyResearchCenter’sBasicAerodynamicsResearchTunnel.Comparisonismadewithpitot-staticprobedatainthefreestreamovertherange0m/s–55m
7、/s.ComparisonwithLDVismadeintherecirculationregionbehindthestepandinawell-developedboundarylayerinfrontofthestep.Goodagreementisfoundinallcases.Keywords.LITA,laservelocimetry,laseranemometry,laser-inducedthermalacousticsSubjectclassification.ExperimentalFluidDynamics1
8、.Introduction.LaserDopplerVelocimetryisthe‘goldstandard’forsingle-pointopticalvelocimetrymethods.Itisroutinelyappliedtoagrea
