简介：Thispaperreviewsnumericalandexperimentalinvestigationsofsheet/cloudcavitationcarriedoutattheSt.AnthonyFallsLaboratoryandattwocollaboratingfacilities(VersuchsanstaltFürWasserbau,Obernach,GermanyandOsakaUniversity,Japan)formorethanadecade.Althoughsignificantadvanceshavebeenmadeintheanalysisofthisflowseveralissuesarestillunresolved.Thepurposeofthispaperistoexaminetheoverallfeaturesoftheproblem,reviewtheprogressmadetodateandsuggestavenuesfornewinvestigation.

简介：Inthispaper,recentmeasurementsoftipvortexflowwithandwithoutcavitationcarriedoutinCavitationMechanismTunnelofChinaShipScientificResearchCenter(CSSRC)arepresented.TheelliptichydrofoilwithsectionNACA662-415wasadoptedastestmodel.High-speedvideo(HSV)camerawasusedtovisualizethetrajectoryoftipvortexcoreandtheformoftipvortexcavitation(TVC)indifferentcavitationsituations.LaserDopplervelocimetry(LDV)wasemployedtomeasurethetipvortexflowfieldinsometypicalsectionsalongthevortextrajectorywiththecaseofcavitationfree.Stereoparticleimagevelocimetry(SPIV)systemwasusedtomeasurethevelocityandvorticitydistributionswithandwithoutcavitation.Seriesmeasurementresultssuchasvelocityandvorticitydistributions,thetrajectoryoftipvortexcore,thevortexcoreradius,cavitysizeandcavitationinceptionnumberwereobtained.Theresultsdemonstratedthattheminimumpressurecoefficientinthevortexcoreobtainedbyflowfieldmeasurementwasquitecoincidentwiththetipvortexcavitationinceptionnumberobtainedundertheconditionofhighincomingvelocityandlowaircontent.AndTVCwoulddecreasethevortexstrengthcomparingwiththecasewithoutcavitation.

简介：Thesheet/cloudcavitationisofagreatpracticalinterestsincethehighlyunsteadyfeatureinvolvessignificantfluctuationsaroundthebodywherethecavitationoccurs.Moreover,thecavitatingflowsarecomplicatedduetothethermaleffects.ThepresentpapernumericallystudiestheunsteadycavitatingflowsaroundaNACA0015hydrofoilinthefluoreketoneandtheliquidnitrogenwithparticularemphasisonthethermaleffectsandthedynamicevolution.Thenumericalresultsandtheexperimentalmeasurementsaregenerallyinagreement.Itisshownthatthetemperaturedistributionsarecloselyrelatedtothecavityevolution.Meanwhile,thetemperaturedropismoreevidentintheliquidnitrogenforthesamecavitationnumber,andthethermaleffectsuppressestheoccurrenceandthedevelopmentofthecavitatingflow,especiallyatalowtemperatureinthefluoroketone.Furthermore,thecavitatingflowsarecloselyrelatedtothecomplicatedvortexstructures.Thedistributionsofthepressurearoundthehydrofoilisamajorfactoroftriggeringtheunsteadysheet/cloudcavitation.Atlast,itisinterestingtofindthatoneseesasignificantthermaleffectonthecavitationtransition,asmallvalueofσ/2ɑisrequiredinthethermo-sensitivefluidstoachievethesimilarcavitationtransitionthatoccursinthewater.

简介：TheunsteadycavitationevolutionaroundtheClark-Yhydrofoilisinvestigatedinthispaper,byusinganimprovedfilter-basemodel(FBM)withthedensitycorrectionmethod(DCM).Toimprovethepredictionaccuracy,thefilterscaleisadjustedbasedonthegridsize.Thenumericalresultsshowthatasmallfilterscaleiscrucialfortheunsteadysimulationsofthecavitysheddingflow.ThehybridmethodthatcombinestheFBMandtheDCMcouldhelptolimittheoverpredictionoftheturbulentviscosityinthecavitationregiononthewallofthehydrofoilandinthewake.Thelargevalueofthemaximumdensityratio?l/?v,clippromotesthemasstransferratebetweentheliquidphaseandthevaporphase,whichresultsinalargesheetcavitylengthandthevaporfractionriseinsidethecavity.Thecavitypatternspredictedbytheimprovedmethodareverifiedbytheexperimentalvisualizations.Thetime-averagelift,thedragcoefficientandtheprimaryoscillatingfrequencyStforthecavitationnumber?=0.8,theangleofattack,?=8o,ataReynoldsnumberRe=7?105are0.735,0.115and0.183,respectively,andthepredictederrorsare3.29%,3.36%and8.93%.Thetypicalthreestagesinonerevolutionarewell-captured,includingtheinitiationofthesheet/attachedcavity,thegrowthtowardthetrailingedge(TE)withthedevelopmentofthere-entrantjetflow,andthelargescalecloudcavityshedding.ItisobservedthatthecloudcavitysheddingflowinducesthevortexpairsoftheTEvorticesinthewakeandthesheddingvortices.Thepositivevorticityvortexofthere-entrantjetandtheTEvorticesinteractsandmergeswiththenegativevorticityvortexoftheleadingedge(LE)cavitytoproducethesheddingflow.

简介：Amethodispresentedtodeterminesignificantfrequenciesofoscillationsofcavitationstructuresfromhigh-speedcamerarecordingsofaflowarounda2-Dhydrofoil.ThetopviewofthesuctionsideofanNACA2412hydrofoilisstudiedinatransparenttestsectionofacavitationtunnelforselectedcloudcavitationregimeswithstrongoscillationsinducedbytheleading-edgecavityshedding.Theabilityofthemethodtoaccuratelydeterminethedominantoscillationfrequenciesisconfirmedbypressuremeasurements.Themethodcanresolvesubtleflowcharacteristicsthatarenotvisibletothenakedeye.Themethodcanbeusedfornoninvasiveexperimentalstudiesofoscillationsincavitatingflowswithadequatevisualaccesswhenpressuremeasurementsarenotavailableorwhensuchmeasurementswoulddisturbtheflow.