Large contrasting values across adjacent cells
Hi all
Apologies as this is very basic, trying to learn OpenFOAM in preparation for more complex sims. I am running a simple 2D case in potentialFoam, where air is entering from the left and exiting at the top and right, encountering a triangular ridge in the centre. In the solution however I am getting large contrasting values across the cells. (http://i.imgur.com/EqrlL0y.png) I am guessing it is due to the mesh, but checkMesh registers it as okay and I've messed around with increasing cell count/grading with no success. The mesh: http://i.imgur.com/kobL1OJ.png Mesh zoomed to the area of contrast: http://i.imgur.com/4ylAZHa.png blockMeshDict: Code:
/*--------------------------------*- C++ -*----------------------------------*\ Cheers |
I think the solution you got may be physical plausible: There should be a large increasing in pressure at the top of the triangle. I think you gave the pressure here.
I say "plausible" and not "correct" because your problem is perhaps not a potential problem so the potential solution is only a first guess. |
Thank you piu. Sorry though, I should have been more clear - I meant the contrast between the light blue triangular part and the darker blue surroundings, which aligns with the different blocks of the mesh, which made me feel like there was something wrong with the way I'd meshed it.
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Currently you use 10 different blocks. Maybe try less blocks. You can also always try to mesh with snappy. Joshua |
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You used a triangular mesh. Such meshes are known to be diffusive, because they realize a first order approximation. I strongly recommend a hex mesh.
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I believe Sturgeon didn't use a tetrahedral mesh. It is more likely a common visualization issue with ParaView, which decomposes the polyhedral elements into tetrahedra for any good reason I still ignore. You can see the correct mesh by unclicking the option Decompose polyhedra (see attached pics.).
Now coming back to your problem... my initial guess is that it is related with the sudden non-orthogonality in the transition regions. 1st question: Are you using nonOrthogonal correctors? (fvSolution file -> nNonOrthogonalCorrectors) 2nd question: Are you using corrected schemes? (fvScheme file -> laplacianSchemes & snGradSchemes) Attachment 56980 Attachment 56981 |
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My nNonOrthogonalCorrectors is set to 3, as it's copied directly from the cylinder case. Both of the schemes you mentioned are the corrected versions, like in the cylinder case. |
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