1 Commits

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Author	SHA1	Message	Date
Omar SobhandClaude Fable 5	9b097fca0d	rtx-cfd: PISO validated by manufactured solution — after fixing the inverted projection ... PisoSolver was the only major solver in the workspace with no verification of any kind. Writing the MMS harness for it (tests/mms_piso.rs) and inspecting the implementation found the census's defect species again: - The pressure correction had its SIGN inverted: it solved -lap(p') = +rho div(u*)/dt and then corrected with u = u* - (dt/rho) grad(p'), so each projection DOUBLED the divergence instead of removing it. - The momentum sweeps froze the near-wall lines (1..ny-1) and the pressure correction skipped the outer ring of cells (1..nx-1) — both exactly the defects repaired in SIMPLE. - The "explicit" predictor read neighbours the same sweep had already overwritten, so the step depended on sweep order. - The pressure gradient was dropped entirely on the last interior face. Rewritten as a genuinely explicit predictor plus anchored-Neumann projection on the staggered grid, with the conventions SIMPLE now embodies: near-wall lines are unknowns with half-cell wall diffusion, continuity on every cell, boundary faces are prescribed data. Momentum-source and wall-velocity hooks added so the manufactured solution can reach it. Measured (16 -> 32 -> 64): L2 velocity 3.516214e-2, 1.953750e-2, 1.037512e-2 — orders 0.85 and 0.91, first-order upwind's rate — with max |div u| ~ 1e-9 in every cell. The errors agree with SIMPLE's on the same meshes to six or seven significant figures: an implicit under-relaxed outer iteration and an explicit time-marching projection land on the same discrete steady solution, which is what sharing a spatial discretisation must produce and is very hard for two independently wrong solvers to fake. 285 tests, 0 failing. Co-Authored-By: Claude Fable 5 <[email protected]>	2026-08-19 19:28:39 -07:00