Flow around cylinder gives poor results on unstructured meshes in Code_Saturne 9.1

We are testing the standard flow around cylinder case with Code_Saturne 9.1.

For structured meshes, the case works correctly in Code_Saturne 9.1.

However, with unstructured meshes, we could not obtain reasonable results. We tested both 2D/quasi-2D and 3D unstructured meshes, and also tested Reynolds numbers Re=200 and Re≈3900.

Observed behavior in Code_Saturne:

- No clear vortex shedding / Karman vortex street
- Poor wake field
- Abnormal velocity or pressure distribution near the outlet
- Outlet backflow messages such as `Incoming flow detained ... outlet faces`

For comparison, we ran the same meshes and the same Reynolds numbers in OpenFOAM, and the results were normal, with the expected wake/vortex behavior.

So the issue seems specific to Code_Saturne with unstructured meshes for the cylinder wake case.

Could you please advise whether this is a known limitation, a recommended setup issue, or a possible bug? Are there recommended settings for unstructured meshes in this case, especially for outlet boundary conditions, gradient reconstruction, or turbulence modeling?

Comienza reproduciendo el caso estándar de flujo alrededor de un cilindro con las mallas no estructuradas 2D/cuasi-2D y 3D indicadas, en Re=200 y Re≈3900. Compara la configuración de la condición de contorno de salida, la reconstrucción de gradientes y el modelo de turbulencia con las ejecuciones con mallas estructuradas y con OpenFOAM. Se considera terminado cuando se haya determinado si el comportamiento se debe a un problema de configuración, a una limitación conocida o a un error de Code_Saturne, con recomendaciones respaldadas o un defecto reproducible.

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