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Quads vs Triangles for lid-driven cavity flow

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Old   January 24, 2025, 10:11
Default Quads vs Triangles for lid-driven cavity flow
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Giorgio
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Dear Foamers,

I am comparing quads and triangles for a lid driven cavity flow. I am using blockMesh to generate the quadrilateral (hexa) mesh, and Salome for the triangular (prismatic) mesh.

The viscosity is 1e-5 and I am using pisoFoam with the k-epsilon model.

After running the simulation for 5 seconds, the results are very different: the flow computed with quads is much more developed, see pictures below.

QUADS:


TRIA:


I am obviously using the same parameters and schemes for the two simulations. The spacing is delta x = 0.02 for both meshes.

Does anybody have any idea what can cause the difference?
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Old   January 24, 2025, 14:24
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Yes - with a triangulated mesh, there is much more non-orthogonality to the flow through the mesh faces. You therefore need to adjust your solver settings, as per solving on a tet mesh. In the end, it's often just simplest with OF to avoid tet/triangulated meshes.
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Old   January 25, 2025, 03:55
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Indeed, I thought it was non-orthogonality but then it should at least get better when using orthogonality corrections. And it's not, the solution looks exactly the same with orthogonality corrections. How do you suggest to set up the solver for tets?
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Old   January 25, 2025, 05:07
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As I said earlioer - I avoid using tets in OpenFOAM; I have found that it is just too difficult to get stable and accurate simulations with tet meshes. You can google and find threads like Openfoam is not succesful for tetrahedral meshes, which contain some advice (esp on gradient schemes etc.) BUT be warned - the stabilising emasures add numerical diffusion (ie degrade the solution) and you still might not get good convergence or stability.

Just avoid tris/tets if you can and use quads or polys.
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