CFD analysis of journal bearing hydrodynamic lubri

CFDanalysisofjournalbearinghydrodynamiclubricationbyBinghamlubricantK.P.Gertzos,P.G.Nikolakopoulos,C.A.PapadopoulosDepartmentofMechanicalEngineeringandAeronautics,UniversityofPatras,GR-26504Patras,GreecearticleinfoArticlehistory:Received6June2007Receivedinrevisedform27January2008Accepted10March2008Availableonline9May2008Keywords:JournalbearingBinghamfluidYieldstressComputationalfluiddynamics(CFD)FLUENTabstractDesignofsmartjournal-bearingsystemsisanimportantissuethatopensupthepossibilityforsemi-activedynamiccontrolofbearingbehavior.Recentstudiesshowthatthereisanincreasinginterestindesigninghydrodynamicallylubricatedbearingsusingelectro-rheologicalfluids(ERFs)ormagneto-rheologicalfluids(MRFs).BothsmartfluidsbehavelikeBinghamfluids,andthustheBinghamplasticmodelisusedtodescribethegreaseandtheelectro-rheological(ER)andmagneto-rheological(MR)fluidsbehaviorofthenon-Newtonianfluidflow.TheperformancecharacteristicsofahydrodynamicjournalbearinglubricatedwithaBinghamfluidarederivedbymeansofthree-dimensionalcomputationalfluiddynamics(3-DCFD)analysis.TheFLUENTsoftwarepackageisusedtocalculatethehydrodynamicbalanceofthejournalusingtheso-called‘‘dynamicmesh’’technique.Theresultsobtainedfromthedeveloped3-DCFDmodelarefoundtobeinverygoodagreementwithexperimentalandanalyticaldatafrompreviousinvestigationsonBinghamfluids.Journal-bearingperformancecharacteristics,suchasrelativeeccentricity,attitudeangle,pressuredistribution,frictioncoefficient,lubricantflowrate,andtheangleofmaximumpressure,arederivedandpresentedforseverallengthoverdiameter(L/D)bearingratiosanddimensionlessshearnumbersT0oftheBinghamfluid.TheabovediagramsarepresentedintheformofRaimondiandBoydcharts,andcaneasilybeusedinthedesignandanalysisofjournalbearingslubricatedwithBinghamfluids.Thecoreprofileformedinthebearingisalsocalculatedandpresentedforvariousbearingeccentricities,L/Dratios,andshearnumbersT0,andfoundtobeinverygoodagreementwithpreviousexperimentalandtheoreticalinvestigations.Theanalysispresentedhereleadstochartsthatcouldbeusedbythedesignerengineertodesignsmartjournalbearings.&2008ElsevierLtd.Allrightsreserved.1.IntroductionThebehaviorofmanygreaselubricants,aswellaselectro-rheological(ER)andmagneto-rheological(MR)fluids[1]pro-posedas‘‘smart’’lubricants,iswelldescribedbytheBinghammodelofnon-Newtonianfluidflow.AmajordifferencefromtheNewtonianfluidflowisthattheBinghammodelischaracterizedbytwoparameters:(a)yieldstressand(b)viscosity.Whenthestressonthelubricantislessthantheyieldstress,thematerialisrigidandaregioncalledthe‘‘core’’isformed;exceedingtheyieldstressleadstoaquasi-Newtonianflow.StudiesofBinghamfluidlubricationdatebacktotheexperi-mentalworkofCohenetal.[2],ongreaseswhichactlikeBinghammaterials.Milne[3]examinedajournal-bearingmodelbothexperimentallyandtheoreticallyandconcludedthatcoresareformednearthebearingattheregionofmaximumfilmthicknessandnearthemovingshaftattheregionoftheminimumfilmthickness.TheextentofthiscoreformationdependsonlyonthegeometricalconditionatthebearingandthedimensionlessyieldstressT0.Batra[4]studiedonlythecaseofattachedcoresinajournalbearing,butshowedthatbothfloatingandattachedcoresmayoccur.HefoundthattheloadcapacityandthemomentoffrictionofthebearingwithaBinghammaterialarelargerthanthatwithaNewtonianmaterial.Wadaetal.[5]developedthegeneraltheoryofaBinghamsolidinhydrodynamiclubrication,establishingthecoreformationandalsoappliedtheirtheorytoastepbearing[6].Theirtheoryfindsbothafloatingrigidcoreandcoresthatadheretosurfaces.HayashiandWada[7]developedamoregeneralmodifiedReynoldsequationthatincludestheeffectsofcorrelationofshearstresseswiththevelocitygradientsinthecircumferentialandaxialdirections.Finally,theyappliedtheirtheorytoajournalbearingandobtainedthetheoreticalcoreprofileformedinthebearingaswellasthebearingperformance[8].Theyalsoobservedthecoreformationonabearingmadeofatransparentmaterialandmeasuredboththepressuredistributionandthejournaldisplacements.TheexperimentalresultsoftheseworksareusedinthispapertovalidatetheobtainednumericalresultsARTICLEINPRESSContentslistsavailableatScienceDirectjournalhomepage::10.1016/j.triboint.2008.03.002Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](C.A.Papadopoulos).TribologyInternational41(2008)1190–1204foraBinghammaterial.ExperimentalresultsfromvarioustypesofgreasesarepresentedmorerecentlybyMutulietal.[9].Tichy[10]obtaineddifferentmodifiedReynoldsequationswhicharedependentonthepossiblelocalformationofarigidcore,whichmaybeeitherattachedtothesurfaceorfloatingbetweenthesurfaces.Resultsarepresentedforasqueezefilmdamperandjournalbearing.Healsomentionsthattheanalysismaybeusefultothosestudyinglubricationissuesandtryingtopredictthebehaviorofelectro-rheologicalfluids(ERFs).Kimetal.[11]developedamathematicalmodeltoinvestigatetheinfluenceofthelubricantrheologicalpropertiesontheconditionsthatoccurinsliderandjournalbearings.Peng[12]studiedthehydrodynamiccharacteristicsofajournalb