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

11

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