CFDandDNSmethodologiesdevelopmentforfuelbundlesimulationsOriginalResearchArticle

Developmentandapplicationofcomputationalfluiddynamics(CFD)anddirectnumericalsimulation(DNS)approachestothereproductionofcoolantflowinsidenuclearfuelbundlesarediscussed,focusingontheadvantagesandlimitationsofthedifferentmethodologiesandontheirsynergeticpotential.HighReynoldsnumberflowcasesareanalyzedwiththeadoptionofanimprovedanisotropicturbulencemodel,whichincludesanon-linearstressstraincorrelationandanenhancednearwalltreatment.ThecapabilityofthemodeltopredictthecoolantflowdistributioninsiderodbundlesisshownanddiscussedonthebaseofcomparisonwithexperimentaldataforavarietyofgeometricalandReynoldsnumberconditions.Inparticularpredictionsforwallshearstresses,velocity,andsecondaryflowdistributionsareshown.Moreover,DNScomputationsareperformedadoptinganalgorithmbasedonthefinitedifferencemethod,extendedtoboundaryfittedcoordinatesystemsinordertoefficientlyconcentrategridsnearthedistortedwallboundaries.Thevalidityandsignificanceoftheresultsisdiscussedunderlyingtheimportanceoftheinsightsintotheturbulencestructure.ThecalculationsarefurtherextendedtohigherReynoldsnumbers,whichcannotingeneralbetreatedwithDNSapproach,renouncingtotheestimationofthehigher-ordermoments,butlimitedtotheevaluationoftheaveragedvelocityprofiles,turbulenceintensitiesandReynoldsstresses.