Mason Shopperly

research · note · in motion

Ahmed body — y⁺ pass on the baseline grid

Wall-resolved versus wall-modelled. What the residual histogram says about the inflation layer.

Ahmed-25 baseline U_x on the symmetry plane — body, slanted-back separation, wake recirculation. The pass below is being run against this M25 baseline.
Baseline — U_x on the symmetry plane (M25, t=3600). The y⁺ pass is being run on this case; the actual y⁺ map is the next pass's output.
Lane
research
State
Active
Last touched
2026-04-25
Tools
OpenFOAM · Python
Depth
■■□□□□ 2 / 6

Where the workflow is now

The baseline Ahmed body grid runs on the multi-node server with a kOmegaSST RANS configuration in OpenFOAM 12. The drag is in the right ballpark but not converged enough to stand on; the y⁺ map shows the inflation layer is fighting the wake separation.

What this pass is for

Drop the first wall-cell height until y⁺ < 1 across the body and the wake. Re-run, compare drag convergence and residual decay against the existing baseline. The point is not "make it match" — the point is to understand which part of the disagreement is the wall model and which part is the geometry.

Next

Re-run with y⁺ < 1 in the wake; compare drag convergence. Then inspect the residual histogram and decide whether the inflation layer needs more layers or just a finer first cell.

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