INTRODUCTION.
Theinnova*ve ImmersedMeshtechnologyinKARALITCFDhasbeenusedtoperformvalida*onsagainsttheAhmedBodyfor twodifferentflowscenarios.Althoughthe valida*on presented here is based on a 2Drepresenta*on,it isevidentthatsomeofthekeyflow‐fieldfeatures for the twodiffering 25‐degreeand35‐ degreecaseshavebeencaptured.
CASESETUP.
Usingthe powerof the ImmersedBoundary (IB) method in KARALIT,the AhmedBodymodelgeometry(STL format) isdirectly immersedinto a backgroundCartesiangrid.Preprocessingtakesjustseconds, as theuserdoesnothave todealwith*me‐consumingmeshgenera*on.
Fig1.ImmersedMeshrepresenta3onoftheAhmedBody.
FINDINGS.
The computa*ons accurately predict thetwoverydifferentflowregimesattherearo f t he body. The fo l l ow ing keyobserva*onsweremade.
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KARALIT CFD VALIDATION:Ahmed Body.
Ahmed Validation_june 2012
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• 2Dmeshcomprising77kcells• 15‐cellextrusionlayeronsurface• Ground‐confinedExternalFlowapp• Spalart‐Allmarasturbulencemodel• Wallfunc*on,y+~100• 2nd‐ordersymmetricTVDdiscre*za*on• 40m/sinflowvelocity• Re=2.8x106basedonbodyheight• Implicitcoupledsolver• 7‐coreparallelcomputa*ons• Fullcasesetupfromscratchinabout5‐10minutes
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• Theflowseparatesover the slant forthe35‐degreecase,whereas in the 25‐degreecase it mostly remainsadached.
• Asa resultofthe flowsepara*onovertheslant,theWakeinthe35‐degreecase is largerthanforthe25‐degreescenario.
• The U‐velocityprofilesovertheslantandinthewakeofthebodycompare favorablytoexperimentsandpreviouscalcula*ons(eg.,Craeet.al.2001).
Fig2. Streamlines forflowatrear of Ahmed Body ‐25‐degreecase(top)and35‐degreecase(boEom).
CONCLUSION.
The calcula*ons undertaken with the KARALIT CFD code using the Immersed Mesh technique predict the correctdistribu*onsandtrendsofthestreamlinesandvelocityfieldattherearofthebody.
Thesecalcula*onsare extendedtothefull 3Dcomputa*ons.Representa*onoftheside vor*cesandtheirimpactsontheflowboundarylayerovertheslantareexpectedtohaveasignificantimpactontheresults.
Fig 3. Comparisons of Uvelocityatslantand inthewake of the Ahmed Bodyforthe25‐degreecase.
Fig 4. Comparisons of Uvelocityatslantandinthewake of the Ahmed Bodyfor35‐degreecase.
Further inves*ga*on of the Ahmed Body flow field using different turbulence models available in the code is alsoan*cipated.
Thesecalcula*onsdemonstratetheaccuracyof theKARALITCFDcodepredic*ons,withminimalsetupeffort forquitechallengingflow‐fieldscenarios.
Exploit the immersed value
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Ahmed Validation_june 2012
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