Current Practice Unstructured Grid CFD Results For 3rd AIAA High . - NASA

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Engineering, Test & TechnologyBoeing Research & TechnologyCurrent Practice UnstructuredGrid CFD Results for 3rd AIAAHigh Lift Prediction WorkshopAndrew Cary, Mohamed Yousef, Mori Mani, and Pei LiBoeing Research and TechnologyJanuary 12, 2018Copyright 2017 Boeing. All rights reserved.

Boeing Research & Technology Aeromechanics TechnologyOverview Completed series of simulations based on High Lift PredictionWorkshop 3 cases to assess flow solvers, committee-providedgrids, and turbulence models Specific focus on JAXA Standard Model without pylon (Case 2a) Emphasis is on comparing CFD results, not comparison to experiment CFD Solvers: BCFD, CFD , GGNS Grids: JAXA (D), ANSA (E), VGRID (C) Turbulence Models: Spalart-Allmaras (SA), SA-QCR, SA-RC-QCR Principal results: Different CFD codes on same/similar meshes with same turbulencemodel generate similar results Mesh and turbulence model differences lead to different results Once significant flow separation occurs, families of pseudo-solutionattractors appear that are associated with flow separation from differentslat bracketsCopyright 2017 Boeing. All rights reserved.

Boeing Research & Technology Aeromechanics TechnologyJSM Case overview (case 2a)Slat bracketsMach 0.172Rec 1.93Mc 529.2 mmCopyright 2017 Boeing. All rights reserved.

Boeing Research & Technology Aeromechanics TechnologyMesh Comparison - SurfaceComparable faces, despitedifferent resolutionTighter cornerresolutionJAXA Grid (D)Grid SeriesGrid TypeC1 - VGRIDD – JAXAE – ANSAE2 - ANSA (fine)TetrahedraMixed ElementMixed ElementMixed ElementCopyright 2017 Boeing. All rights reserved.ANSA Grid (E)Number ofVolume Cells96.6M120M107M165MNumber ofVolume .81MNumber ofHex/Prism cellsN/A81.3M79.5M129M

Boeing Research & Technology Aeromechanics TechnologyMesh Comparison - VolumeFiner off-bodyresolutionJAXA Grid (D)Grid SeriesGrid TypeC1 - VGRIDD – JAXAE – ANSAE2 - ANSA (fine)TetrahedraMixed ElementMixed ElementMixed ElementCopyright 2017 Boeing. All rights reserved.ANSA Grid (E)Number ofVolume Cells96.6M120M107M165MNumber ofVolume .81MNumber ofHex/Prism cellsN/A81.3M79.5M129M

Boeing Research & Technology Aeromechanics TechnologyVolume Mesh StatisticsCumulative cellsPrism Cells Bins of wall distance (geometric growth)Cells colored by aspect ratio (green division is AR 2)35% cells are within y approx. 5080% cells are within 5% MAC of bodyCopyright 2017 Boeing. All rights reserved.

Boeing Research & Technology Aeromechanics TechnologyMesh Comparison – Volume MetricsJAXA Grid (D)ANSA Grid (E) ANSA grid packs more cells in lower part of boundary layer ANSA grid has less overall resolution between 5% and 25% chord,but more resolution at about 1 chord Image does not reflect spacing/distribution on surfaceCopyright 2017 Boeing. All rights reserved.

Boeing Research & Technology Aeromechanics TechnologyLift Coefficient: Result Consistency Results with same grid andturbulence model generallyconsistent JAXA (SA-RC-QCR) resultsshow strong consistency acrossflow solvers, users ANSA results show largerE2spread for both SA-QCR andSA-RC-QCR; primarilyassociated with slat bracketseparation Solutions cluster based onlocation of slat bracketseparations (annotation)Copyright 2017 Boeing. All rights reserved.Mesh: JAXA, ANSA, VGRID, EPICSolver: BCFD, CFD , GGNSTurbulence Model:SA,SA-QCR,SA-RC-QCR

Boeing Research & Technology Aeromechanics TechnologyLift Coefficient: SA-RC-QCR Recommended variation ofSA turbulence model Results sensitive to meshbut reflect different pseudosolution attractorsE2Copyright 2017 Boeing. All rights reserved.Mesh: JAXA, ANSA, VGRID, EPICSolver: BCFD, CFD , GGNSTurbulence Model:SA,SA-QCR,SA-RC-QCR

Boeing Research & Technology Aeromechanics TechnologyLift Coefficient: Grid Sensitivity ANSA mesh appears more sensitive to turbulence model thanJAXA mesh Solution variation with iteration less than symbol size; typically 3-5orders of magnitude residual convergenceCopyright 2017 Boeing. All rights reserved.

Boeing Research & Technology Aeromechanics TechnologyLift Coefficient – Overall Comparison General agreement untilsignificant flow separation Consistent trends for given mesh(multiple flow solvers andturbulence models) JAXA grid particularly tightlyclustered Adapted mesh results similar untilfinal angle of attack Large spread near key areas(CLmax, AoAmax) limitsengineering usefulness in theseregionsRelative difference from experimental data to facilitate comparisonCopyright 2017 Boeing. All rights reserved.Mesh: JAXA, ANSA, VGRID, EPICSolver: BCFD, CFD , GGNSTurbulence Model:SA,SA-QCR,SA-RC-QCR

Boeing Research & Technology Aeromechanics TechnologyPseudo-Solution Robustness (soln interp)ANSA, CL 2.61JAXA, CL 2.76ANSA, CL 2.52Restarted from JAXA BCFD SA-QCR, 18.58 Interpolate JAXA solution onto ANSA grid and reconvergeCopyright 2017 Boeing. All rights reserved.

Boeing Research & Technology Aeromechanics TechnologyPseudo-Solution Robustness (change CFL)BCFD, JAXA grid, SA-QCR Changing CFL number switches pseudo-solution sometimes(indication of strength of attractor) Need flow solver convergence to assess grid, turbulence model,but what if multiple solutions?Copyright 2017 Boeing. All rights reserved.

Boeing Research & Technology Aeromechanics TechnologyTime-Accurate Simulation ImpactInstantaneousSolutionTime-AveragedSolution Start time-accurate DDES solutionon JAXA grid, SA-QCR, 20.59 Time-averaged solution shows noseparation Lift comparable to RANSRANS SolutionCopyright 2017 Boeing. All rights reserved.

Boeing Research & Technology Aeromechanics TechnologyTime-Accurate Simulation Pressure DistributionInboardOutboard Inboard pressure cut (A-A) compare well to RANS; show littlevariation Outboard pressure cut (H-H) shows average flow is attached;improved comparison to experimental measurementCopyright 2017 Boeing. All rights reserved.

Boeing Research & Technology Aeromechanics TechnologySummary Effort focused on current technology flow solvers with committeeprovided meshes and standard turbulence models Generally good agreement among solvers for same grid andturbulence model Grid convergence has not been assessed Significant amount of grid very close to aircraft JAXA committee-provided grid shows less variation in results thanANSA grid, but had less off-body resolution Solver identifies multiple pseudo-solutions that can sometimes beperturbed to different attractors Interpolation of new solutions Change CFL number Running time accurate may lead to improved comparison toexperimentCopyright 2017 Boeing. All rights reserved.

Copyright 2014 Boeing. All rights reserved.

Boeing Research & Technology Aeromechanics TechnologyC-VGRID meshCopyright 2017 Boeing. All rights reserved.

Boeing Research & Technology Aeromechanics TechnologyEPIC meshCopyright 2017 Boeing. All rights reserved.

Emphasis is on comparing CFD results, not comparison to experiment CFD Solvers: BCFD, CFD , GGNS Grids: JAXA (D), ANSA (E), VGRID (C) Turbulence Models: Spalart-Allmaras (SA), SA-QCR, SA-RC-QCR Principal results: Different CFD codes on same/similar meshes with same turbulence model generate similar results

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