aerodynamics best practices 8.02
TRANSCRIPT
Best Practices for External Aerodynamics
Best Practices Document
For lower Mach numbers, the pressure-based solver with an incompressible fluid formulation will likely yield better convergence behavior.If vortex shedding (large bluff bodies, fully separated flow, etc.) is important, a DES approach is recommended.– Beware using URANS for this type of analysis
Range of Applicability
Domain
Poly meshes: Use polyhedral expansion and match surface growth rate with volume growth behaviorTrimmer meshes: No special treatment needed
Half Models
No
Yes
The new “curvature correction” option can be applied to the SST K-Omega model when flows with high streamline curvature are important.– This model is more difficult to converge, so may need to run
without CC first, then turn it on.
“Vorticity Confinement” can be used to help prevent vortices from dissipating downstream.
Physics
Mesh
“C-Grid” Topology– Cp values are all within experimental
uncertainty, even with TE separation– CL values deviate <0.2% prior to TE
separation (a~12deg)• ~2% after TE separation
NACA 0012 – Effect of Cell Type
NACA0012, 15 deg
NACA0012, 15 deg
Structured Quad57k Cells
Polyhedra22k Cells
Cartesian Trim16k Cells
Mesh (Continued)
Surface Refinement
AIAA Drag Prediction Workshop 3Purpose to benchmark CFD codes for drag predictionWing/Body configuration with/without fairing (Mach 0.75)Utilized unstructured Cartesian trim-cell mesh with prism layers– Volumetric Controls to refine mesh in critical regions– Nominal grid contains 12.4M cells
AIAA DPW3 – Background
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AIAA DPW3 – Wing/Body Results
AIAA DPW3 – Wing/Body Results
Re = 3e6 Mach No = 0.75AoAs = -2, -1, 0, 1, 2
Simulation :Mesh – 29 million Cells (Half model)Steady Coupled SolverK-Omega SSTTransition Modeling
DLR Drag Prediction Workshop 2
Mesh - Trimmer
AIAA HiLiftWS1 – Configuration
Manual / AutomaticShocks, wakes, vortices, shear layers, etc.Volumetric controlsTrimmer wake refinement (anisotropic)
Mesh Adaption
Wake
Prevents smearing for 1-2 chords downstream
It’s generally not possible to enforce correct wall y+ everywhere, so focus on the important areasAvoid putting the first cell in the y+ = 10-50 range
Prism Layers
C-Grid provides best TE solution– Not always feasible for complex wing shapes
O-Grid without retraction provides best compromise with automated meshingO-Grid with retraction…is default behavior!Keep in mind: is the actual trailing edge really a knife-edge?
NACA 0012 – Effect of Trailing Edge Mesh
NACA0012, 15 deg
NACA0012, 15 deg
C-Grid22k Cells
O-Grid, No Retract10k Cells
O-Grid, Retract10k Cells
Blunt Trailing Edges
No
Yes (Almost)
Should refine the wake here