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NASA Ames Research Center Contribu4on to GMGW-1
WilliamM.Chan
NASAAmesResearchCenter
PID02
1stAIAAGeometryandMeshGenera?onWorkshopDenver,COJune3-4,2017
SummaryofGridsGenerated
Case Code(s) Star4ngGeometryModel
GridType NumberGridLevels
HL-CRMfullgap ChimeraGridTools STEP OversetStructured 4
HL-CRMpar?allysealed ChimeraGridTools STEP OversetStructured 1
GMGW-1,DenverCO,June2017 2
Chan,W.M.,DevelopmentsinStrategiesandSoQwareToolsforOversetStructuredGridGenera?onandConnec?vity,AIAA2011-3051.Chan,W.M.,Gomez,R.J.,Rogers,S.E.,Buning,P.G.,BestPrac?cesinOversetGridGenera?on,AIAA2002-3191
ChimeraGridTools(CGT)-Acollec?onofsoQwaretoolsforpre-andpost-processingofCFDsimula?onusingstructuredoversetgrids-Geometry/GridTools:geometry/gridprocessing,algebraicandhyperbolicsurfaceandvolumegridgenera?on-AnalysisTools:gridquality,aerodynamicloads,flowsolu?on-HighLevelTools:OVERGRIDgraphicalinterface,ScriptLibrary(200+macros)
GeometryImportandPrepara4on
GMGW-1,DenverCO,June2017 3
• ImportSTEPfileintoANSA-Generatetriangula?onthataccuratelyresolvesgeometry-Gridresolu?oninhighcurvatureregions(leadingedges)needstobeequalorhigherthanthestructuredsurfacegridstobegenerated• Noimportdifficul?es
• Nomodifica?onsperformedongeometry
• Lessonslearned-IntroduceCADedgealongallleadingedges-BecarefulontolerancesnearCADfaceboundaries(doesnotaffectstructuredoversetsurfacemeshgenera?oniflocalsurfacenormalsarealmostconsistent)
MeshGenera4onProcessSummary
GMGW-1,DenverCO,June2017 4
• Surfacemeshgenera?on-Iden?fydomainsforalgebraicmeshing(2,3,or4ini?alcurves)hyperbolicmeshing(1ini?alcurve)-Prescribegridpointdistribu?ononini?alcurves-CreatesurfacemeshusingTFIorhyperbolicmarching• Volumemeshgenera?on(near-body:hyperbolic,off-body:Cartesian)• Domainconnec?vity:Distance-basedholecuts(C3P),orX-rayhole-cut(OVERFLOW-DCF)• Meshexportformats:Gridsystem-PLOT3DOversetmeshconnec?vitydata–XINTOUT• En?reprocessrecordedinTclscriptsystembasedonCGTScriptLibrary
5
Hyperbolicgridmarchingdistanceschosentoprovideproperoverlapatmediumlevel(e.g.,5-pointoverlapfor5-pointflowsolverstencil)Insomeregions:-Insufficientoverlapatcoarselevel-Toomuchoverlapatfineandextrafinelevels
Coarse Medium
Fine ExtraFine
MeshGenera4onIssues(I)ParameterAdjustmentsatDifferentMeshResolu4onLevels(A)
6
Finergridspacinginconcavecornersinfinerlevels-Needtoadjustsmoothingparametersforhyperbolicmarching
CoarseMediumFineExtra-fine
MeshGenera4onIssues(I)ParameterAdjustmentsatDifferentMeshResolu4onLevels(B)
7
TwoproblemswerediscoveredaQerini?alversionofmeshsystem1.Averysmallnumberofnega?vecellvolumesfound-Disregardedini?allysinceflowsolverisnodecenteredFix:lowersmoothingvalues2.TFIsurfacemesharoundflapleadingedgehadlargestretchingra?o-Badprojec?ontogeometrydefini?onfromlackofleadingedgegeometrycurve-Surfacegridpointsareongeometry,butsurfacecellsarefarfromgeometryFix:introduceleadingedgecurve,redoTFIandprojec?ontogeometrydefini?on
MeshGenera4onIssues(II)Nega4veCellVolumesandBadProjec4on
MeshSta4s4cs
GMGW-1,DenverCO,June2017 8
GeometryModel
GridType GridLevel
Blocks SurfaceGridPoints
VolumeGridPoints
OrphanPoints
HLCRMFullGap
OversetStructured Coarse 72 0.27M 24.1M 2
Medium 72 0.51M 65.4M 6
Fine 76 1.02M 189.3M 16
Extra-Fine
102 2.08M 564.9M 119
HLCRMPar?alSeal
OversetStructured Medium 73 0.53M 66.3M 22
MeshEvalua4on:SurfaceandVolumeMeshes
GMGW-1,DenverCO,June2017 20
• Must-pass• Jacobian>0atvolumemeshver?cesascomputedbyOVERFLOWflowsolver• Cellvolume>0(decomposi?oninto6tets)• Noself-intersec?onofvolumegridpointsagainstsurfacegrid
• Mostly-pass• Stretchingra?omostlyaround1.2
• Adherencetomeshingguidelines• Trailingedgegridspacingmadetobecon?nuousaroundfinitethicknesstrailingedge• Mul?-griddablenumberofpointsineachdirec?onisnotneededsinceOVERFLOWflowsolverhasnosuchrestric?ons
• Lessonslearned• Needna?veCAD,STEP,IGESgeometryinterroga?ongridtool(e.g.,EGADS)1.projectsurfacegridpointsontogeometrydefini?on2.checkdistanceofsurfacegridpointsfromgeometrydefini?on
21
Count,loca?on,andspread(CGT:OVERGRID)
Total=25,sparsepointsawayfromsurface
MeshEvalua4on:OversetConnec4vity(I)OrphanPoints
22
-Cellvolumera?ohistogramtable(CGT:intchk)andloca?onmap(CGT:OVERGRID)-Badra?o=>gradientscannotbetransferredaccuratelybetweengrids
Cellvolumera?o<0.01
CellVolumeRa?o#Pts.%Total0.5<=R<=1.0271426848.260.2<=R<0.5170503630.320.1<=R<0.267023211.920.01<=R<0.15250489.340.001<=R<0.0196310.17R<0.001210.37E-03
Otherapributesthatcouldbechecked-Cellaspectra?o,orienta?on
MeshEvalua4on:OversetConnec4vity(II)Compa4bilityofCellAKributesBetweenFringePoint
andDonorStencil
23Convertedfringepoints
-Insufficientgridoverlaptosupportdoublefringelocally-Op?ontoconvertfromdoublefringetosinglefringe=>full5-pointdifferencingstencilnotsupportedinflowsolver(loweraccuracy,robustness)
SinglefringeregionLoca?onmap(CGT:OVERGRID)
MeshEvalua4on:OversetConnec4vity(III)ConversiontoLowerNumberofFringeLayers
24
Histogramtable(CGT:intchk)andloca?onmap(CGT:OVERGRID)
StencilQualityCount%TotalQ=0.000.000.0<Q<0.100.000.1<=Q<0.200.000.2<=Q<0.348580.170.3<=Q<0.4121200.420.4<=Q<0.5146600.510.5<=Q<0.6140540.480.6<=Q<0.7195040.670.7<=Q<0.8247880.850.8<=Q<0.9232800.800.9<=Q<1.0453171.56Q=1.0257385894.54
Stencilquality<0.26
MeshEvalua4on:OversetConnec4vity(IV)DonorStencilQuality
GMGW-1,DenverCO,June2017 25
MeshEvalua4on:FlowSolverTestSeeHigh-LiQPredic?onWorkshop3talksonOVERFLOWandLAVAresults
CoarseMediumFineX-Fine
GMGW-1,DenverCO,June2017 26
-Developconnec?onbetweensurfacegridgenera?onsoQwareandgeometryinterroga?ontool(e.g.,usingEGADS)tobringsurfacegridpointsontona?veCAD,STEP,orIGES-Developmoreautomatedoversetsurfacemeshgenera?onalgorithmandsoQware(“StrategiesTowardAutoma1onofOversetStructuredSurfaceGridGenera1on”,tobepresentedatAIAAAvia?on2017)
-DevelopmoregridqualitychecksoQware(minmax,histograms,contourplotsofvariousgridapributes)
FutureTechnology
Summary
• Oversetsurfacegridgenera?onrequiresthemostmanualeffort• Crea?onofgridsystemswithdifferentmeshresolu?onlevelsusingthescrip?ngapproachisnotassimpleasfirstan?cipated(marchingdistanceandsmoothingparameteradjustments)
• Needtobeabletoprojectsurfacegridpointsbacktona?veCAD,STEP,orIGESgeometrydefini?on
• Needmoregridqualitychecktools
GMGW-1,DenverCO,June2017 27
Task(Mediumfullgapmesh,1stmeshgenerated) Time(hr.) %ofTotal
Geometryprocessing/Ref.triangula4ongenera4on 3.75 5.5
Surfacegridgenera4on 56.05 81.7
Volumegridgenera4on 4.50 6.6
Domainconnec4vity(C3P) 1.20 1.7
Inputprep.(flowsolverb.c.,post-processing) 3.1 4.5
Total 68.6 100
Acknowlegement:NASAT3Project,Transforma?veAeronau?csConceptsProgram(ARMD)