Drag Prediction Using NSU3D (Unstructured Multigrid NS Solver)

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Presentation transcript:

Drag Prediction Using NSU3D (Unstructured Multigrid NS Solver) Dimitri J. Mavriplis National Institute of Aerospace Hampton, VA 23666 (USA)

NSU3D Description Unstructured Reynolds Averaged Navier-Stokes solver Vertex-based discertization Mixed elements (prisms in boundary layer) Edge data structure Matrix artificial dissipation Option for upwind scheme with gradient reconstruction No cross derivative viscous terms Thin layer in all 3 directions

Solver Description (cont’d) Spalart-Allmaras turbulence model (original published form) Optional k-omega model Transition specified by zeroing out production term in turbulence model More robust than S-A trip term Based on surface patches Laminar patches Laminar normal distance

Solution Strategy Jacobi/Line Preconditioning Agglomeration multigrid Line solves in boundary layer regions Releives aspect ratio stiffness Agglomeration multigrid Fast grid independent convergence rates Parallel implementation MPI/OpenMP hybrid model DPW runs: MPI on 16 cpu cluster

Performance Convergence in 500 multigrid cycles Grid independent Poor convergence for negative alpha nacelle cases 16 Pentium IV 1.7GHz: Intermediate grids 5 hours for 3M pt grid 7.5 hours for 5M pt grid

Grid Generation Runs based on NASA Langley supplied VGRIDns unstructured grids Tetrahedra in Boundary Layer merged into prismatic elements Sequence of 3 grids for each configuration Transition based on surface patches

Grid Specifications Coarse Medium Fine Wing-Body Points Cells Configuration Coarse Medium Fine Wing-Body Points Cells 1,121,301 6,558,758 3,010307 17,635,283 9,133,352 53,653,279 WB+Nacelle 1,827,470 10,715,204 4,751,207 27,875,222 10,278,588 60,412,948

Intermediate Grid (WB: 3M pts) Transition specified by laminar patches

Intermediate Grid (WB: 3M pts) Transition specified by laminar patches

Intermediate Grid (WBN: 5M pts) Transition specified by laminar patches

Solution on Intermediate Grid (CL=0.5) Matching CL

Solution on Intermediate Grid (CL=0.5) Matching Incidence

Solution on Intermediate Grid (CL=0.5) Matching CL

Solution on Intermediate Grid (CL=0.5) Matching Incidence

Lift vs. Incidence (Wing-Body) Large Lift overprediction (incidence shift)

Surface Pressure at y/b=0.411(WB) Solution converges with grid refinement Poor match with experiment for specified CL Better match for specified incidence

Lift vs. Incidence (WB-Nacelle) Large Lift overprediction (incidence shift)

Surface Pressure at y/b=0.411(WBNacelle) Solution converges with grid refinement Poor match with experiment for specified CL Better match for specified incidence

Drag Polar (Wing-Body) Coarse grid inadequate Correct shape, slight underprediction

Drag Polar (Wing-Body-Nacelle) Coarse grid inadequate Correct shape, slight underprediction Convergence issues at negative incidences

Moment (Wing-Body) Poor moment prediction Related to incidence shift

Moment (Wing-BodyNacelle) Poor moment prediction Related to incidence shift

Incremental Drag Within 2 to 4 counts at CL=0.5 Transition effects cancel out More discrepancies at lower lift

Incremental Moment Good prediction in spite of poor absolute values Cross over well predicted Discrepancies at lower lift

Drag Rise Curves Medium grids, transition General trend, Drag underpredicted Cl vs incidence issues

Flow Details Separation bubble on WB-Nacelle (fine grid)

Flow Details Strong shock inboard pylon (-2 deg) Ahead of specified transition region on lower wing

Conclusions CL – Incidence Issues Better success at prediction of increments Grid Generation approach may be more important than actual resolution Aero is still a tough problem Worthy of funding