Adimpleappearsonafreesurfacewhilerotatingacylindertankfilledwithliquid.Thedimplestartstoconcentricallydeepertoadrainportatthebottomcenterofthetank.Overtime,thedimplepenetratesthedrainport,afreesurfaceformsalongandslenderstringshapeinthetank,andaso-calledvortexing(aircore)phenomenonoccurs.Thegenerationofavortexcoredependsonthesizeofthetankanddrainport,andonthepropertiesoftheliquidinthetank.Inthisstudy,theliquidlevelandthetimeatwhichthevortexcoreisinitiallygeneratedarenumericallyinvestigatedusingdifferentvaluesoftankdiameter,drainportdiameter,andinitialtankrotationalspeeds.Insteadofafullthree-dimensionalanalysis,atwo-dimensionalaxisymmetricsimulationisconducted.Themomentumconservationequationinthecircumferentialdirectionisadditionallysolvedinthetwo-dimensionalmeshsystem.Severalnon-dimensionalvariablesarecreated:theratiooftheaircoregenerationdistanceandtankdiameter,thediameterratioofthetankanddrainport,therotationalReynoldsnumber,therotationalFroudenumber,andtherotationalWebernumber.Finally,thenon-dimensionalaircoregenerationdistanceiscorrelatedwiththeothernon-dimensionalparameters.
