ModellingandcomputationofcavitationandboilingbubblyflowswiththeNEPTUNE_CFDcodeOriginalResearchArticle

ThispaperfocusesonthemodellingandthenumericalsimulationwiththeNEPTUNE_CFDcodeofcavitationphenomenaandboilingbubblyflows. Compressible,unsteady,turbulent3Dtwo-phaseflowiscomputedbytheNEPTUNE_CFDsolver,developedjointlybyEDFR&DandCEA.Thenumericalapproachisbasedonafinite-volumeco-locatedcell-centredapproachandmakesuseofanoriginalpressure-basedmulti-fieldcouplingalgorithm[Mechitoua,N.,etal.,2003.Anunstructuredfinitevolumesolverfortwo-phasewater/vapourflowsmodellingbasedonanellipticorientedfractionalstepmethod.In:Proceedingsofthe10thInternationalTopicalMeetingonNuclearReactorThermal-Hydraulics(NURETH10),Seoul,Korea]. Thecavitationnucleicomefromwallnucleationorarepre-existingintheflow.Generatedvaporbubblesareadvectedbytheflowandexpandintheregionswherethelocalpressureisbelowthesaturationwithatendencytoagglomerateintoslugbubbles. Themodelpredictionscomparedwithexperimentaldataonenoughselectivelocalvariablesshowedthatsatisfactoryagreementcouldbeobtainedwithoutanyfloatingparametertofitthedata. Thesecondpartofthepaperdealswithboilingbubblyflowthroughamixingdevicerepresentingtheeffectofafuelassemblyspacergridequippedwithmixingblades(DEBORA-mixingexperiment,CEA,Grenoble).Localmeasurementsofthevoidfractionareprovideddownstreamthemixingenhancer.Thecomputationscomparefavourablywiththeexperimentalresults;inparticular,theglobaleffectofthemixingbladeswasobserved.Amodificationoftheclassicalnucleateboilingmodelisproposedtoovercomethestrongmodelsensitivitywithrespecttonearwallgridrefinement.