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Improving convergence - high viscosity problem |
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#1 |
New Member
Julia Fed
Join Date: Jul 2020
Location: UK
Posts: 4
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Hi,
I have been having problems with convergence while running OpenFOAM simulations. I have made my mesh in ANSYS (refined it a few times), converted it to OpenFOAM, and it works for low viscosities. The problem is that I need to reach very high values of viscosity (about 3000). Decreasing the timestep doesn't help and the Courant number explodes pretty quickly. At the moment, I am using icoFoam, a uniform inlet velocity of 0.00023 m/s, Timestep = 0.005. my fvSchemes file is:
and fvSolution: Maybe I can improve something here? Thank you, Julia |
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#3 | |
Senior Member
Santiago Lopez Castano
Join Date: Nov 2012
Posts: 354
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Quote:
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#4 |
Senior Member
Join Date: Sep 2013
Posts: 353
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These mandate a really orthogonal high quality grid. If your checkMesh output has a nonOrthogonality above let's say 5 you should probably consider switching those out, or you'll loose accuracy. Going from orthogonal to uncorrected to corrected and limited results in higher accuracy on bad meshes. Solving with uncorrected or orthogonal will result in better convergence at the cost of accuracy if the mesh does not allow for it.
Code:
laplacianSchemes { default Gauss linear orthogonal; -> corrected } snGradSchemes { default orthogonal; -> corrected } Code:
divSchemes { default none; div(phi,U) Gauss linear; -> limitedLinear 1 or linearUpwind grad(U) } Code:
PISO { nCorrectors 4; --> increase these nNonOrthogonalCorrectors 0; -> maybe go up to 1 here } Code:
solvers { p { solver PCG; preconditioner DIC; tolerance 1e-06; relTol 0.05; } pFinal { $p; relTol 0; } U { solver smoothSolver; smoother symGaussSeidel; tolerance 1e-05; relTol 0; } } |
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