Investigation-into-pressure-pulsations-in-a-centri

InvestigationintopressurepulsationsinacentrifugalpumpusingnumericalmethodssupportedbyindustrialtestsR.Spencea,*,J.Amaral-TeixeirabaClydePumpsLimited,149NewlandsRoad,Cathcart,GlasgowG444EX,UnitedKingdombSchoolofEngineering,CranfieldUniversity,Cranfield,BedfordshireML430AL,UnitedKingdomReceived16March2007;receivedinrevisedform21September2007;accepted1October2007Availableonline6October2007AbstractTheoperationofcentrifugalpumpscangenerateinstabilitiesandpressurepulsationsthatmaybedetrimentaltotheintegrityandperformanceofthepump.Inthepresentstudyanumericalinvestigationofthetimevariationofpressurewithinacompletecentrifugalpumpwasundertaken.Arangeofparametersandthreeflowrateswereinvestigatedandthepulsationswereextractedat15differentlocationscoveringimportantpumpregions.Thetransientflowresultscomparedreasonablywithexperimentaldataobtainedinalimitedexperimentalsurveyandclearlyindicatedthepumplocationsexperiencingthelargestpulsationlevels.Itwasalsonotedthatmonitoringpulsationsatthetopdeadcentreofthepumpvolutecasingwouldprovideabetterindicationofinternalpumppulsationsthanmoni-toringatthedischarge.2007ElsevierLtd.Allrightsreserved.1.IntroductionCentrifugalpumpshavebeendevelopedandrefinedovermanyyears.Inpracticethedesignofboththeimpellerandvolutearecomplex,withnumerousgeometricalparametersbeingrequiredtoidentifyadesignthatwillformahydraulicallyefficientpump.Evenwithtriedandtesteddesignsitiswellknownthattheoperationofrotody-namicpumpscanresultinthegenerationofinstabilitiesandpressurepulsations,forexample[1,2],whichcanaffectthemechanicalintegrityofthepump,resultingincompo-nentfatigue[3]excessivevibrationand/ornoise[4].Cur-rently,accuratepredictionsofthemagnitudeofpressurepulsationsarenoteasilyachievablebynumericalmeansandexperimental/empiricalresultsareoftenstillusedintheevaluationofnewdesigns[5].Regardlessofthedesignprocessused,thefinaldecisionregardingthesuitabilityofanysignificantlynewpumpdesignisusuallymadefollowingphysicaltesting.Thesetestsareoftenexpensiveintermsoftimeandresources,forexample,duetothemanufacturingofpatternequip-ment,theprototypepumpitselfaswellastheassemblyandtheuseoftestfacilities.Gradually,pumpmanufactur-ersareturningtocomputationaltechniquestostudydesignfeatures.Ingersoll-Randpublishedanumberofpapersintheearlyto-mid1990sstudyingcentrifugalpumpcompo-nents,i.e.[6].Sulzerfollowedanumberofyearslater[7]andWeirPumpsLimitedadoptedCFX-TASCflowtowardstheendofthe1990s[8].Typicallytheseinvestiga-tionsareconductedwithaviewtoreducing,oreliminatingthenumberoftestsconductedandtohighlightanyunde-sirabledesigncharacteristicsatanearlystage.AlthoughcommercialCFDpackageshavebeenusedtopredicttimedependentpressurepulsations,computationalfacilitiesseemtohavelimitedmostofthatworktosimulatingthevoluteandimpellerinteractionsonly,withoutthesuctioninletbranchandleakageflowpathsbeingconsidered,[9].Tamm[10]includedtheimpeller,voluteandleakageflowpath,butonlyconductedasteadystateanalysis.Thecurrentworkaimstoimprovethequalityandscopeofpreviousworkrelatedtopressurepulsationsbyperforming0045-7930/$-seefrontmatter2007ElsevierLtd.Allrightsreserved.doi:10.1016/j.compfluid.2007.10.001*Correspondingauthor.Currentaddress:SgurrEnergyLtd,79CoplawStreet,Glasgow,G427JG,UK.E-mailaddress:[e-mail](R.Spence).fluidAvailableonlineat(2008)690–704simulationsinvolvingthecompletehydraulicpumpgeom-etry.Thenumericalmodelincorporatesallofthemajorflowpathsinapumpencompassingthesuctioninlet,impeller,leakagepathwaysandthevolutecasing.Theworkfocusesonareducedscaleversionofahighenergyimpellerinadoubleentry,singlestagepumparrangement.Theunderstandingofpressurepulsationsbypumpmanu-facturersseemssurprisinglylimited.Noofficialstandardsexistforsafelevelsofpressurepulsationsinpumps;theonlyindustryadoptedguidelineisaguaranteeoflessthan3%variationinthepumpoutletpressure.Yet,itisnotknownwhetheralimitationof3%variationinthedis-chargecorrespondstoasafelimitatotherlocationswithinapump.Thereforeadetailedassessmentofpressurepulsa-tionsinboththeimpellerandvolutehasbeenperformedtogaugewhetherthe3%adoptedlimitatthedischargeactu-allyprovidesanyguaranteeforothercriticalpartsofthepump.Theanalysiscoversthreeflowratesoveraflowrangeextendingfromthepumpdutycondition(1.00Qn)toacommonpumpminimumoperatingpointof25%ofthedutycondition(0.25Qn).Theanalysespresentedherearepartofalargerpara-metricstudyinvestigatingtheeffectofinternalgeometryonpressurepulsationswithinthepump.Duetothecon-straintsinvolvedinsuchalargestudy,oneadditionalaimofthisworkwastoshowthatareasonableestimateofpressurepulsationsandtrendsinpressurepulsationscanbeachieved,fordifferingpumpgeometries,inareason-abletimeframebynumericalmeans.2.PumpgeometryThefocusoftheinvestigationisadoubleentry,doublevolutecentrifugalpump.Thestudycomprisestwopumpgeometricalarrangements.ThesearrangementswillbetermedAandBrespectively.Fig.1providestwocross-sections,Fig.1.Axialandverticalcross-sectionsthroughadoubleentry,doublevolutecentrifugalpump.Table1MaincharacteristicsofpumparrangementsL