简介：Asimulationiscarriedoutforthepressurefluctuationdrivenbythewaterhammer,basedonajointuseoftheonedimensionalmethodofcharacteristics(MOC)andthethree-dimensionalfinitevolumemethod(FVM).Thethree-dimensionalvisualizationofthecavitationinducedbythewaterhammerisimplemented,andthetemporalandspatialanalysesofextremeregionsaremade.Apracticalcaseofthewaterhammer,withtheminimumboundarypressurehigherthanthesaturatedvaporpressurecondition,issimulated.Thesimulationpredictionthatthecavitationwouldoccurinthefrontofthegasketcouldservesomeguidelinefortheoptimizationofindustrialdesigns.

简介：Theinceptionoftipvortexcavitationisverysensitivetowaterquality.Inordertoquantifytheeffectofwaterqualityontheinceptionoftipvortexcavitation,wedevelopamotionmodeltodescribethemigrationandgrowthofnucleiinwater.Ananalyticalsolutionofmigrationofnucleiinavortexflowisobtainedsothatthecapturetimesofvariousnucleicanbegivenoutdirectly.Acriterionisbuilttodeterminethecriticalnucleusinacertainnucleispectradistribution.Tensilestrengthofthecriticalnucleusisusedtoquantifytheeffectofwaterqualityandcorrectthetipvortexcavitationinceptionnumber.Finallythischangeofcavitationinceptionnumberiscomparedwithexperimentalresultstovalidateourmodel.

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简介：稳固的墙上的表成穴的开始的预言被认出了很困难，自从它被边界层流动显著地影响特征，免费原子核的人口，原子核控制了墙粗糙，在液体的溶解空气的数量等等。开始怎么被水质量和背景流动的条件影响，足够地没被弄明白特征。在这研究，高从免费原子核加速表洞的开始的观察被进行为一二维会聚--分叉的嘴流动，表洞在此就嘴喉咙下游地形成。表成穴的开始进程上的溶解空气和免费的流速度的数量的效果被检验。另外，水泡原子核密度，众所周知是为成穴开始的重要因素，被在隧道安装的过滤器消极地控制。从观察，原子核数字密度显著地影响表洞而非另外的二个参数的形成，这被证实。在与大原子核数字调节密度，表洞不形成，并且冒泡的成穴相反出现。在有小原子核数字密度的情况中，表洞从一个单个流动原子核形成并且streamwisely并且spanwisely发展。处于有中等原子核数字密度的条件，表洞也形成，但是是shorter/更狭窄的streamwisely/spanwisely，由于流动在形成的表洞附近的另外的原子核的相互作用。

简介：Whentheshockwaveofunderwaterexplosionpropagatestothesurfacesofdifferentboundaries,itgetsreflected.Then,anegativepressureareaisformedbythesuperpositionoftheincidentwaveandreflectedwave.Cavitationoccurswhenthevalueofthenegativepressurefallsbelowthevaporpressureofwater.Animprovednumericalmodelbasedonthespectralelementmethodisappliedtoinvestigatethecavitationeffectofunderwatershockneardifferentboundaries,mainlyincludingthefeatureofcavitationeffectneardifferentboundariesandtheinfluenceofdifferentparametersoncavitationeffect.Intheimplementationoftheimprovednumericalmodel,thebilinearequationofstateisusedtodealwiththefluidfieldsubjectedtocavitation,andthefieldseparationtechniqueisemployedtoavoidthedistortionofincidentwavepropagatingthroughthemeshandthesecond-orderdoublyasymptoticapproximationisappliedtosimulatethenon-reflectingboundary.Themainresultsareasfollows.Asthepeakpressureanddecayconstantofshockwaveincreases,therangeofcavitationdomainincreases,andthedurationofcavitationincreases.Asthedepthofwaterincreases,theinfluenceofcavitationonthedynamicresponseofsphericalshelldecreases.

简介：Usingthesupercavitationphenomenonisnecessarytoreachhighvelocitiesunderwater.Supercavitationcanbeachievedintwoways:naturalandartificial.Inthisarticle,thesimulationofflowsaroundatorpedowasstudiednaturallyandartificially.Thevalidityofsimulationusingtheoreticalandpracticaldatainthenaturalandartificialphaseswasevaluated.Resultsshowedthatthesimulationswereconsistentwiththelaboratoryresults.Theresultsindifferentinjectioncoefficientrates,injectionangles,andcavitationnumberswerestudied.Theobtainedresultsshowedtheimportanceofcavitationnumber,injectionratecoefficient,andinjectionangleincavityshape.Atthefinallevel,determiningtheperformanceconditionsusingtheDesignofExperiment(DOE)methodwasemphasized,andtheperformanceofcavitationnumber,injectionratecoefficient,andinjectionangleindragandliftcoefficientwasstudied.Theincreaseininjectionangleinthelowinjectionratecoefficientresultedinadiminisheddragcoefficientandthatinthehighinjectionratecoefficientresultedinanenhanceddragcoefficient.

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：Thetipvortexcavitation(TVC)noiseofmarinepropellersisofinterestduetotheenvironmentalimpactsfromcommercialshipsaswellasforthesurvivabilityofnavalships.Duetocomplicatedflowandnoisefieldaroundamarinepropeller,atheoreticalapproachtotheestimationofTVCnoiseispracticallyunrealizable.Thus,estimationofprototypeTVCnoiselevelisrealizedthroughextrapolationofthemodelTVCnoiselevelmeasuredinacavitationtunnel.Inthisstudy,forthepredictionofprototypeTVCnoiselevelfromamodeltest,anovelscalinglawreflectingthephysicalbasisofTVCisderivedfromtheRayleigh-Plessetequation,theRankinevortexmodel,theliftingsurfacetheory,andotherphysicalassumptions.ModelandprototypenoisedatawereprovidedbySamsungHeavyIndustries(SHI)forverification.Inapplyingthenovelscalinglaw,similitudeofthespectraofnucleiisappliedtoassumethesamenucleidistributioninthetipvortexlineofthemodelandtheprototype.ItwasfoundthattheprototypeTVCnoiselevelpredictedbythenovelscalinglawhasbetteragreementwiththeprototypeTVCnoisemeasurementthantheprototypeTVCnoiselevelpredictedbythemodifiedITTCnoiseestimationrule.

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

简介：Thispaperdescribesanovelsharpinterfaceapproachformodelingthecavitationphenomenainincompressibleviscousflows.Aone-fieldformulationisadoptedforthevapor-liquidtwo-phaseflowandtheinterfaceistrackedusingavolumeoffluid(VOF)method.PhasechangeattheinterfaceismodeledusingasimplificationoftheRayleigh-Plessetequation.Interfacejumpconditionsinvelocityandpressurefieldaretreatedusingalevelsetbasedghostfluidmethod.Thelevelsetfunctionisconstructedfromthevolumefractionfunction.Amarchingcubesmethodisusedtocomputetheinterfaceareaattheinterfacegridcells.Aparallelfastmarchingmethodisemployedtopropagateinterfaceinformationintothefield.Adescriptionoftheequationsandnumericalmethodsispresented.Resultsforacavitatinghydrofoilarecomparedwithexperimentaldata.