徐州工程學院畢業(yè)設計外文翻譯學生姓名左林冬學院名稱機電工程學院專業(yè)名稱機械設計制造及其自動化指導教師陳鳳騰2011年05月27日Researchonlowcavitationinwaterhydraulictwo-stagethrottlepoppetvalveAbstract:Cavitationhasimportanteffectsontheperformancesandlifespanofwaterhydrauliccontrolvalve,suchasdegradingefficiency,intensenoise,andseverevibration.Two-stagethrottlevalveisapracticableconfigurationtomitigatecavitation,whichisextensivelyusedinwaterhydraulicpressurereliefvalvesandthrottlevalves.Thepressuredistributioninsideamediumchamberlocatedbetweentwothrottlesofatwo-stagethrottlevalveisinvestigatedthroughnumericalsimulations.Theeffectsofthepassagearearatioofthetwothrottlesandtheinletandoutletpressuresonthepressureinsidethemediumchamberareexamined.Thesimulationresultsindicatethat(a)thepressureinsidethemediumchamberisnotconstant,(b)thelocationsofmaximumandminimumpressuresinsidethemediumchamberarebothfixed,whichwillnotvarywiththepassagearearatioortheinletandoutletpressures,and(c)theratioofthepressuredropacrossthefrontthrottletothetotalpressuredropacrossthetwo-stagethrottlevalveisnearlyconstant.Thecriticalcavitationindexofthetwo-stagethrottlevalveisthenestablished.Asemiempiricaldesigncriterionisobtainedforthewaterhydraulictwo-stagethrottlevalve.Thecorrelationbetweenthecriticalcavitationindexandthepassagearearatioofthetwothrottlesisinvestigated.Relevantvalidationexperimentsareconductedatacustom-manufacturedtestingapparatus.Theexperimentalresultsareconsistentwiththesimulatedones.Furtheranalysesindicatethat(a)thelargebackpressurecanimprovenotonlytheanti-cavitationcapabilitybutalsothetotalloadrigidityofthewaterhydraulictwo-stagethrottlevalve,(b)anappropriatepassagearearatiowillbebeneficialforimprovingtheanti-cavitationcapabilityofthewaterhydraulictwo-stagethrottlevalve,and(c)thewaterhydraulictwo-stagethrottlevalvewithapassagearearatioof0.6wouldhavethebestanti-cavitationperformancewiththelowestriskofcavitation.Keywords:computationalfluiddynamicssimulationcavitationloadrigiditypassagearearatiotwo-stagethrottlevalvewaterhydraulics1INTRODUCTIONWaterhydraulicsystemsareoperatedwithrawwater(puretapwater)substitutingformineraloil.Theyhaveadvantagesintermsofdurability,reliability,safety,andcleanness.Suchsystemsarebecomingmoreandmorepopular,especiallyinfieldsofsteelandglassproduction,coalandgoldmining,foodandmedicineprocessing,nuclearpowergeneration,oceanexploration,andunderwaterrobotics15.Becausetheopeningofawaterhydrauliccontrolvalveisverysmallcomparedwiththatofoilvalve,thewaterflowvelocitythroughthewaterhydrauliccontrolvalveislargerunderthesamepressurecondition；thuscavitationerosionmayoccurduetothehighvapourpressureofwater.Cavitationhasanimportanteffectontheperformanceandlifespanofwaterhydrauliccontrolvalve,suchasdegradingefficiency,intensenoise,andseverevibration.Previously,anumberofstudiesontherelationshipsbetweencavitationanddischargecoefficient,thrustforceandpressuredistributionsinthevalves,andmitigationofcavitationdamagewerecarriedoutthroughincreasingoutletpressureofvalves,modifyingshapesofthrottles,addingstagesofvalves,selectinganti-corrosionmaterialsforparts,andcontrollingmaximumfluidtemperatureandflowvelocity.Tsukijietal.6investigatedcavitationbyflowvisualizationinhydraulicpoppet-typeholdingvalvestoreducecavitation.Somemeasureswereemployedtodiminishnoiseandcavitationthroughcontrollingflowrate,upstreampressure,downstreampressure,andvalveliftincaseofconvergingflow.Aoyamaetal.7studiedexperimentallytheunsteadycavitationperformanceinanoilhydraulicpoppetvalve.Itwasfoundthat,asabsolutevaluesofthevariationratesofinletandoutletpressureincreased,theincipientcavitationindexexhibitedatendencytodecrease,whereasthefinalcavitationindexatendencytoincreaseunderallgeometricalparameters.Astheabsolutevaluesofthevariationratesofinletandoutletpressurefurtherincreased,thehysteresisbetweentheincipientandfinalcavitationindiceswouldbecomelargerthaneverforeachcombinationofthevalveandvalveseat.Ishiharaetal.8studiedoilflowunsteadinesseffectoncavitationphenomenaatsharp-edgedorifices.Therateofpressuredropacrosstheorificewaskeptconstant,andcavitationincipienceandfinalewererecordedbyusingscatteredlaserbeamsshowingthat(a)thereexistedtwotypesofcavitation,namely,gaseouscavitationandvapourouscavitation,and(b)cavitationincipienceandfinalevariedwiththeinitialcondition,thetemperatureofhydraulicoil,andtherateofpressuredrop.Johnstonetal.9carriedoutanexperimentalinvestigationofflowandforcecharacteristicsofhydraulicpoppetanddiscvalvesusingwaterastheworkingfluid.Theaxisymmetricvalvehousingwasconstructedfromclearperspextofacilitateflowvisualization；testswereperformedonarangeofdifferentpoppetanddiscvalvesoperatingundersteadyandnon-cavitatingconditions,forReynoldsnumbersgreaterthan2500.Measuredflowcoefficientsandforcecharacteristicsshowedobviousdifferencesdependingonvalvegeometryandopening.Vaughanetal.10conductedcomputationalfluiddynamics(CFD)analysisonflowthroughpoppetvalves.Simulationswerecomparedwithexperimentalmeasurementsandvisualizedflowpatterns.Aqualitativeagreementbetweensimulatedandvisualizedflowpatternswasidentified.However,errorsinthepredictionofjetseparationandreattachmentresultedinquantitativeinaccuracies.Theseerrorswereduetothelimitationsoftheupwinddifferencingschemeemployedandtherepresentationofturbulencebythek1model,whichwasknowntobeinaccuratewhenappliedtorecirculatingflow.Uenoetal.11investigatedexperimentallyandnumericallytheoilflowinapressurecontrolvalveunderanassumptionofnon-cavitatingconditionsforvariousconfigurationsofthevalvesonthebasicsofafinitedifferencemethod.Theyconcludedthatthemainnoiseofthetestingvalveswasgeneratedfromcavitation,andthenoisewasaffectedbythevalveconfiguration.Pressuremeasurementsandflowvisualizationattwolocationsinavalvechamberwerealsoperformedonthebasisoftwo-dimensionalmodels.Throughcomparisonsofthemeasuredandcalculatedresults,severaldesigncriteriaweresetupforlow-noisevalves.Martinetal.12investigatedcavitationinspoolvalvesinordertoidentifydamagemechanismsoftherelatedcomponents.Testswereconductedinarepresentativemetalspoolvalveaswellasamodelbeingthreetimeslarger.Datatakenundernon-cavitatingconditionswithbothofthesevalvesshowedthattheorientationofhigh-velocityangularjetswouldbeshiftedduetovariationsinvalveopeningandReynoldsnumber.Bymeansofhigh-frequencyresponsepressuretransducersstrategicallyplacedinthevalvechamber,thecavitationcouldbesensedthroughthecorrelationofnoisewithacavitationindex.Theonsetofcavitationcouldbedetectedbycomparingenergyspectraforafixedvalveopeningwithaconstantdischarge.Theincipientcavitationindex,asdefinedinthisinvestigation,wascorrelatedwiththeReynoldsnumberforbothvalves.Gaoetal.13performedasimulationofcavitatingflowsinhydraulicpoppetvalvesbymeansofanrenormalizationgroup(RNG)k1turbulencemodel,whichwasderivedfromthenstantaneousNavierStokesequationsbasedontheRNGtheory.Experimentswereconductedtocatchcavitationimagesaroundtheseatofapoppetvalvefromperpendiculardirections,usingapairofindustrialfibrescopesandahigh-speedvisualizationsystem.Thebinarycavitatingflowfielddistributionsobtainedthroughdigitalprocessingoftheoriginalcavitationimageshowedsatisfactoryagreementwithnumericalresults；thevibrationsofvalvebodyandpoppetinducedbythecavitatingflowweredetectedusingavortexdisplacementtransducer,alaserdisplacementmetreandadigitalstraindevice.Itwasconcludedthattheopeningandconeofaconicalvalvehadsignificanteffectsontheintensityofcavitation.However,inthisstudy,onlydownstreamcavitationinceptionvolumewasanalysedinestimatingt