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英文文獻(xiàn)InvestigationintopressurepulsationsinacentrifugalpumpusingnumericalmethodssupportedbyindustrialtestsR.SpenceandJ.Amaral-TeixeiraABSTRACTTheoperationofcentrifugalpumpscangenerateinstabilitiesandpressurepulsationsthatmaybedetrimentaltotheintegrityandperformanceofthepump.Inthepresentstudyanumericalinvestigationofthetimevariationofpressurewithinacompletepumpwasundertaken.Arangeofparametersandthreeflowrateswereinvestigatedandthepulsationswereextractedat15differentlocationscoveringimportantpumplocationsexperiencingthelargestpulsationlevels.Itwasalsonotethatmonitoringpulsationsatthetopdeadcentreofthepumpvolutecasingwouldprovideabetterindicationofinternalpumppulsationsthanmonitoringatthedischarge.1、IntroductionCentrifugalpumpshavebeendevelopedandrefinedovermanyyears.Inpracticethedesignofboththeimpellerandvolutearecomplex,withnumerousgeometricalparametersbeingrequiredtoidentifyadesignthatwillformahydraulicallyefficientpump.Evenwithtrieddesignsitiswellknownthattheoperationofrotodynamicpumpcanresultinthegenerationofthedesignprocessused；thefinaldecisionregardingthesuitabilityofanysignificantlynewpumpdesignisusuallymadefollowingphysicaltesting.Thesetestsareoftenexpensiveintermoftimeandresources,forexampleduetothemanufacturingofpatternequipment,theprototypepumpitselfaswellastheassemblyandtheuseoftestfacilities.Gradually,pumpmanufacturersareturningtocomputationaltechniquestostudydesignfeatures.Typicallytheseinvestigationsareconductedwithaviewtoreducing,oreliminatingthenumberoftestsconductedandtohighlightanyundesirabledesigncharacteristicsatanearlystage.AlthoughcommercialCFDpackageshavebeenusedtopredicttimedependentpressurepulsations,computationalfacilitiesseemtohavelimitedmostofthatworktosimulatingthevoluteandimpellerinteractionsonly,withoutthesuctioninletbranchandleakageflowpathsbeingconsidered.Thecurrentworkaimstoimprovethequalityandscopeofpreviousworkrelatedtopressurepulsationsbyperformingsimulationsinvolvingthecompletehydraulicpumpgeometry.Thenumericalmodelincorporatesallofthemajorflowpathsinapumpencompassingthesuctioninlet,impeller,leakagepathwaysandthevolutecasing.Theworkfocusesonareducedscaleversionofahighenergyimpellerinadoubleentry,singlestagepumparrangement.Theunderstandingofpressurepulsationsbypumpmanufacturersseemssurprisinglylimited.Noofficialstandardsexistforsafelevelsofpressurepulsationsinpumps；theonlyindustryadoptedguidelineisaguaranteeoflessthan3%variationinthepumpoutletpressure.Yet,itisnotknownwhetheralimitationof3%variationinthedischargecorrespondstoasafelimitatotherlocationswithinapump.Thereforeadetailedassessmentofpreesurepulsationsinboththeimpellerandvolutehasbeenperformedtoguaranteeforothercriticalpartsofthepump.Theanalysiscoversthreeflowratesoveraflowrangeextendingfromthepumpdutycondition(1.00oQn)toacommonpumpminimumoperatingpointof25%ofthedutycondition(0.25oQn)Theanalysespresentedherearepartofalargeparametricstudyinvestigatingtheeffectofinternalgeometryonpressurepulsationswithinthepump.Duetotheconstrainsinvolvedinsuchalargestudy,oneadditionalaimofthisworkwastoshowthatareasonableestimateofpressurepulsationsandtrendsinpressurepulsationscanbeachieved,fordifferingpumpgeometries,inareasonabletimeframebynumericalmeans.2、ExperimentalInvestigationSomeexperimentalresultswereavailabletooneoftheauthorsfromindustrialtestsperformedtoexaminepressurepulsationsinareducedscalecontractpump.Thisexperimentalworkperformedanumberofyearsbeforethenumericalanalyses.Thepumpreceivedfluidfromaclosedsystem,suchthatthepumpwassituatedwithabend3.5diametersupstreamandasecondbend4diametersdownstream.Directlyfollowingtheupstreambend,flowstraightenerswerefitteninordertoreducethefloweffectscausedbythebendontheinflowtothepump.TenZtypeKistlerpressuretappingsweremountedonthepump.Pressuretappingswereusedtocollectdataatvariousstationarylocationsaroundthepump.Holesweredrilledatspecificlocationsaroundthepumpandtubeswereusedtoconnectthepressuretransducerstoeachlocation.Thepathdistancefromthetappingpointtothetransducerwaskeptasshortaspossible(10-15omm)toensurethatanyresonantfrequenciescausedbythepathdistanceareabovethemeasuredrange.OneZtypeEntranpressuretransducerwasutilizedintheexperimentaltests.Thistransducerwasmountedintheimpellershroud15ommbehindthesuctionfaceofanimpellerblade.Theelectricalsignalsfromthetransducersweretransferredfromtherotatingelementthestationarydatarecorderviaaslipringarrangementatthenon-driveendofthepump.Thetestringwasrunataninitialspeedof1400RPMovertheflowrange25-125%ofdutywith5-mintaperecordingsofthetransducersbeingtakenateach25%flowincrement.The1.00oQndutyconditionequatedtoaflowrateof500om3/handanominalheadof33.8omfortheinlineimpellerwhenthepumpwasrunat1400RPM.Theflowchangewasachievedbyadjustingaflowvalveasslowlyandassmoothlyaspossible.Arangeoftestswasperformedforanumberofpumpgeometricalarrangements,howeveronlytwoareofparticularinteresthere(termedAandBasdetailedabove).Atimehistoryofthepressurevariationateachoftheabovelocationsisrecorded.Aspectralanalysiswasthenconductedonthisdatawiththepressurepulsationsbeingoutputastheroot-mean-square(RMS)pressurepulsation.Duetothetimeconstraintsinvolvedintheexperimentaltests,detailedperformancedatawasnottaken.Thetestworkwasconductedinaccordancewithnormalindustrialpracticesanditisconsideredthatthepressureswereaccuratewithin1.5%.3、NumericalInvestigationCFX-TASCflowisacommercial3D-CFDcodethatafinite-elementbasedfinite-volumemethodtothetransportequations.Thismethodprovidesthebenefitofretainingthegeometricflexibilityoffinite-elementmethodswhileretainingtheconservationpropertiesofthefinite-volumemethod,I,elownumericalerroronnon-smoothgirds.Thecodeemploysco-locatedstructuredgridsandacoupiedalgebraicmultigridschemetosolvethesystemofequations.Itisafully-implicitsolver,thusitcreatesnotimesteplimitationandisconsideredeasytoimplement.Thisdoesnothaveanybearingonthesteady-statesolution.Butdoeslimittransientcalculationstobeingonlyfirst-orderaccurateintime.TheCFX-TASCflowsolverisalsoacoupledsolvermeaningthatthemomentumandcontinuityequationsaresolvedsimultaneously.Thisapproachreducesthenumberofiterationsrequiredtoobtainconvergenceandnopressurecorrectionstermisrequiredtoretainmassconservation,leadingtoamorerobustandaccuratesolver.Theprogramalsoincludessomepre-andpost-processingcapabilitiesthatarespecificallygearedtowardsturbomachinerycomponents,thesefacilitatethesetupofthemodelandtheexaminationoftheresultsCFX-TASCflowhasaproventrackrecordinturbomachineryapplications,withnumerousitemsofliteraturebeingpublished.3、1ModelgenerationTheimpellergeometrywascreatedusingCFX-Bladehenastwomirroredhalves,usingthemaximumdiameterof366omm.Thebull-noseaspectoftheinlineimpellerdesignproveddifficulttocapturewithinCFX-Bladegen,astheprogramisnotdesignedtomodeldoubleentryimpelleranddoesnotallowforhubprofilesthatterminateinthebullnosearrangement.Toavoidthisproblem,althoughthetruehubeffectivelyfinishedatthepointofsymmetry,afictitioushubwasextendedfromthemidpointofthebullnosetotheimpelleroutletalongtheimpellerlineofsymmetry.Thereforewithonlyslightmodificationstothemeridionalhubprofileasatisfactorymodelwasproducedfortheinlineimpeller.Thestaggeredimpellercouldbeusedwithoutanymodification,asthemeridionalflowpathsforeithersideoftheimpellerdonotconnect.CFX-Turbogridwasusedtogenerategridaroundthebladesoneithersideoftheimpeller,withthegridonbothsidesoftheimpellersbeingidentical.Fortheinlineimpeller,carewastakentoensurethatthegridwasradialatthepositionofthebullnose.ThisisessentialtoaidthecreationofaninterfacebetweentheimpellersinCFX-TASCflow,howeveritalsolimitedthequalityofthegrid.Withaninitialimpellergridestimateofaround500,000modes,itisimmediatelyapparentthatsplittingthisgridbetween12impellerpassagewaysandtheleakageflowwillresultinimpellerpassagewaygridsoflessthanidealsize.Someefforthasbeenmadetofocusonthelessergridsizes,whileincludinggridsaslargeas86,499nodes.AdecisionwastakentoconductthegridindependencecheckusingsteadystateanalysesincorporatingamodelconsistingofhalfapumpIesiximpellerpassagesandhalfpumpvolute(usingsymmetry),astheimpellerinteractionwiththevoluteisextremelyimportant.Thevolutemodelwasidenticalineachofthegridindependenceanalyses,withadistributionsimilartothatusedinthefinalpumpmodel.Itisexpectedthatthisinteractionwillcauselargerdifferencestobeevidentbetweenthegirdsthanisusuallydisplayedingridindependenceforimpelleronlycomparisonsduetotheincreasedcomplexityoftheflowpatterns.Theanalyseswererunatthedutyflowcondition(1.00oQn),boundaryconditionsbeingmassflowatinletandaveragestaticpressureatoutlet,withthemaximumresidualconvergencecriteriabeingsetto1e-4(max).thepressuredatareportedbelowrelatestothevariationinasingleimpellerpassageway(frommidpassagetomidpassage)atasinglepositionwithinthevolute.4、2SolutionparametersAsthemotionoftheimpellerbladesrelativetothestationaryvoluteiscentraltotheinvestigation,theanalysismustinvolvemultipleframesofreference.Inordertopreventtworotor/statorinterfacesbeingperpendiculartoeachotherattheompelleroutlet,theleakageflowpathsandtheimpellergridsweresetintherotationalframeofreference.Thesuctioninletandvolutegridswereinthestationaryframeofreference.Thegridinterfacesusedinthestudycanbesummarizedasfollows:Internalcomponentconnection:generalgridinterface(GGI)Betweentwostationarycomponents:generalgridinterfaceBetweentworotationalcomponents:generalgridinterfaceBetweenrotationalandstationarycomponents:Frozenrotorinterface(steadystateanalysis)Rotor/statorinterface(transientanalysis)Thefrozenrotorinterfaceachievesframechangewithoutrelativepositionchangeovertimeandwithoutinterfacialaveraging.Localflowfeaturesareallowedtopropagate.Aphysicalanalogyistoimagineobservingtheflowbetweenastationaryandrotatingcomponentunderstroboscopiclighting.Therotor/statorinterf