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外文翻译--关于二级液压节流锥阀的低汽蚀研究.doc

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外文翻译--关于二级液压节流锥阀的低汽蚀研究.doc

徐州工程学院毕业设计外文翻译学生姓名左林冬学院名称机电工程学院专业名称机械设计制造及其自动化指导教师陈凤腾2011年05月27日ResearchonlowcavitationinwaterhydraulictwostagethrottlepoppetvalveAbstractCavitationhasimportanteffectsontheperformancesandlifespanofwaterhydrauliccontrolvalve,suchasdegradingefficiency,intensenoise,andseverevibration.Twostagethrottlevalveisapracticableconfigurationtomitigatecavitation,whichisextensivelyusedinwaterhydraulicpressurereliefvalvesandthrottlevalves.Thepressuredistributioninsideamediumchamberlocatedbetweentwothrottlesofatwostagethrottlevalveisinvestigatedthroughnumericalsimulations.Theeffectsofthepassagearearatioofthetwothrottlesandtheinletandoutletpressuresonthepressureinsidethemediumchamberareexamined.Thesimulationresultsindicatethatathepressureinsidethemediumchamberisnotconstant,bthelocationsofmaximumandminimumpressuresinsidethemediumchamberarebothfixed,whichwillnotvarywiththepassagearearatioortheinletandoutletpressures,andctheratioofthepressuredropacrossthefrontthrottletothetotalpressuredropacrossthetwostagethrottlevalveisnearlyconstant.Thecriticalcavitationindexofthetwostagethrottlevalveisthenestablished.Asemiempiricaldesigncriterionisobtainedforthewaterhydraulictwostagethrottlevalve.Thecorrelationbetweenthecriticalcavitationindexandthepassagearearatioofthetwothrottlesisinvestigated.Relevantvalidationexperimentsareconductedatacustommanufacturedtestingapparatus.Theexperimentalresultsareconsistentwiththesimulatedones.Furtheranalysesindicatethatathelargebackpressurecanimprovenotonlytheanticavitationcapabilitybutalsothetotalloadrigidityofthewaterhydraulictwostagethrottlevalve,banappropriatepassagearearatiowillbebeneficialforimprovingtheanticavitationcapabilityofthewaterhydraulictwostagethrottlevalve,andcthewaterhydraulictwostagethrottlevalvewithapassagearearatioof0.6wouldhavethebestanticavitationperformancewiththelowestriskofcavitation.Keywordscomputationalfluiddynamicssimulationcavitationloadrigiditypassagearearatiotwostagethrottlevalvewaterhydraulics1INTRODUCTIONWaterhydraulicsystemsareoperatedwithrawwaterpuretapwatersubstitutingformineraloil.Theyhaveadvantagesintermsofdurability,reliability,safety,andcleanness.Suchsystemsarebecomingmoreandmorepopular,especiallyinfieldsofsteelandglassproduction,coalandgoldmining,foodandmedicineprocessing,nuclearpowergeneration,oceanexploration,andunderwaterrobotics1–5.Becausetheopeningofawaterhydrauliccontrolvalveisverysmallcomparedwiththatofoilvalve,thewaterflowvelocitythroughthewaterhydrauliccontrolvalveislargerunderthesamepressureconditionthuscavitationerosionmayoccurduetothehighvapourpressureofwater.Cavitationhasanimportanteffectontheperformanceandlifespanofwaterhydrauliccontrolvalve,suchasdegradingefficiency,intensenoise,andseverevibration.Previously,anumberofstudiesontherelationshipsbetweencavitationanddischargecoefficient,thrustforceandpressuredistributionsinthevalves,andmitigationofcavitationdamagewerecarriedoutthroughincreasingoutletpressureofvalves,modifyingshapesofthrottles,addingstagesofvalves,selectinganticorrosionmaterialsforparts,andcontrollingmaximumfluidtemperatureandflowvelocity.Tsukijietal.6investigatedcavitationbyflowvisualizationinhydraulicpoppettypeholdingvalvestoreducecavitation.Somemeasureswereemployedtodiminishnoiseandcavitationthroughcontrollingflowrate,upstreampressure,downstreampressure,andvalveliftincaseofconvergingflow.Aoyamaetal.7studiedexperimentallytheunsteadycavitationperformanceinanoilhydraulicpoppetvalve.Itwasfoundthat,asabsolutevaluesofthevariationratesofinletandoutletpressureincreased,theincipientcavitationindexexhibitedatendencytodecrease,whereasthefinalcavitationindexatendencytoincreaseunderallgeometricalparameters.Astheabsolutevaluesofthevariationratesofinletandoutletpressurefurtherincreased,thehysteresisbetweentheincipientandfinalcavitationindiceswouldbecomelargerthaneverforeachcombinationofthevalveandvalveseat.Ishiharaetal.8studiedoilflowunsteadinesseffectoncavitationphenomenaatsharpedgedorifices.Therateofpressuredropacrosstheorificewaskeptconstant,andcavitationincipienceandfinalewererecordedbyusingscatteredlaserbeamsshowingthatathereexistedtwotypesofcavitation,namely,gaseouscavitationandvapourouscavitation,andbcavitationincipienceandfinalevariedwiththeinitialcondition,thetemperatureofhydraulicoil,andtherateofpressuredrop.Johnstonetal.9carriedoutanexperimentalinvestigationofflowandforcecharacteristicsofhydraulicpoppetanddiscvalvesusingwaterastheworkingfluid.Theaxisymmetricvalvehousingwasconstructedfromclearperspextofacilitateflowvisualizationtestswereperformedonarangeofdifferentpoppetanddiscvalvesoperatingundersteadyandnoncavitatingconditions,forReynoldsnumbersgreaterthan2500.Measuredflowcoefficientsandforcecharacteristicsshowedobviousdifferencesdependingonvalvegeometryandopening.Vaughanetal.10conductedcomputationalfluiddynamicsCFDanalysisonflowthroughpoppetvalves.Simulationswerecomparedwithexperimentalmeasurementsandvisualizedflowpatterns.Aqualitativeagreementbetweensimulatedandvisualizedflowpatternswasidentified.However,errorsinthepredictionofjetseparationandreattachmentresultedinquantitativeinaccuracies.Theseerrorswereduetothelimitationsoftheupwinddifferencingschemeemployedandtherepresentationofturbulencebythek–1model,whichwasknowntobeinaccuratewhenappliedtorecirculatingflow.Uenoetal.11investigatedexperimentallyandnumericallytheoilflowinapressurecontrolvalveunderanassumptionofnoncavitatingconditionsforvariousconfigurationsofthevalvesonthebasicsofafinitedifferencemethod.Theyconcludedthatthemainnoiseofthetestingvalveswasgeneratedfromcavitation,andthenoisewasaffectedbythevalveconfiguration.Pressuremeasurementsandflowvisualizationattwolocationsinavalvechamberwerealsoperformedonthebasisoftwodimensionalmodels.Throughcomparisonsofthemeasuredandcalculatedresults,severaldesigncriteriaweresetupforlownoisevalves.Martinetal.12investigatedcavitationinspoolvalvesinordertoidentifydamagemechanismsoftherelatedcomponents.Testswereconductedinarepresentativemetalspoolvalveaswellasamodelbeingthreetimeslarger.DatatakenundernoncavitatingconditionswithbothofthesevalvesshowedthattheorientationofhighvelocityangularjetswouldbeshiftedduetovariationsinvalveopeningandReynoldsnumber.Bymeansofhighfrequencyresponsepressuretransducersstrategicallyplacedinthevalvechamber,thecavitationcouldbesensedthroughthecorrelationofnoisewithacavitationindex.Theonsetofcavitationcouldbedetectedbycomparingenergyspectraforafixedvalveopeningwithaconstantdischarge.Theincipientcavitationindex,asdefinedinthisinvestigation,wascorrelatedwiththeReynoldsnumberforbothvalves.Gaoetal.13performedasimulationofcavitatingflowsinhydraulicpoppetvalvesbymeansofanrenormalizationgroupRNGk–1turbulencemodel,whichwasderivedfromthenstantaneousNavier–StokesequationsbasedontheRNGtheory.Experimentswereconductedtocatchcavitationimagesaroundtheseatofapoppetvalvefromperpendiculardirections,usingapairofindustrialfibrescopesandahighspeedvisualizationsystem.Thebinarycavitatingflowfielddistributionsobtainedthroughdigitalprocessingoftheoriginalcavitationimageshowedsatisfactoryagreementwithnumericalresultsthevibrationsofvalvebodyandpoppetinducedbythecavitatingflowweredetectedusingavortexdisplacementtransducer,alaserdisplacementmetreandadigitalstraindevice.Itwasconcludedthattheopeningandconeofaconicalvalvehadsignificanteffectsontheintensityofcavitation.However,inthisstudy,onlydownstreamcavitationinceptionvolumewasanalysedinestimatingtheanticavitationcapability,whereastheeffectsofoutletpressurewerenotconsidered.Oshimaetal.14experimentallyinvestigatedtheinfluencesofachamferlengthinthevalveseat,bthepoppetangle,andctheoiltemperatureontheflowcharacteristicsandthecavitationphenomena,usingwaterinsteadofoilastheworkingmediuminwaterpoppetthrottles.Thecavitationphenomenaweredirectlyobservedandthepressuredistributionbetweenthevalveseatandpoppetsurfacewasmeasuredinwaterpoppetthrottles.Comparisonanalysesontheconditionofcriticalcavitationwereconductedbetweenoilandwater.Itwasfoundthatthedischargecoefficientandthecriticalcavitationnumberforwaterpoppetthrottleswereconsiderablydifferentfromthoseofoilones,duetothehighdensityandlowviscosityofwater.Recently,Liuetal.15,16investigatedexperimentallytheflowandcavitationcharacteristicsofatwostagethrottlein

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