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Initial residuals not converging and stay high values |
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April 30, 2019, 15:01 |
Initial residuals not converging and stay high values
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#1 | |
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Joe lee
Join Date: Nov 2018
Posts: 59
Rep Power: 8 |
I am trying to do the mesh convergence test by increasing the mesh refinement to see at what level will the drag force converge. I used simpleFoam as I want to solve for steady-state solution. However, I found that when the mesh refinement level increases, the residual values especially Ux, Uy and p keep increasing. Here is the residuals of the mesh (I will call this meshA) with refinement level = (edge = surface = region = 2; no layer):
And for mesh (I will call this meshB) with refinement level = (edge = surface = region = 4; boundary layer = relatvie 0.3; no. of layer = 3 (81.1% generated)): Also, the forceCoeffs become unstable for high refinement level(meshB), while it is stable at low refinement level(A). forceCoeffs of meshA: forceCoeffs of meshB: What may be the cause? Does this imply the solution maybe transient? Thanks a lot! FYI, here is my controlDict for both settings: Quote:
Code:
solvers { p { solver GAMG; smoother GaussSeidel; tolerance 1e-7; relTol 0.01; } Phi { $p; } U { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; } k { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; } epsilon { solver smoothSolver; smoother GaussSeidel; tolerance 1e-8; relTol 0.1; nSweeps 1; } } SIMPLE { nNonOrthogonalCorrectors 0; consistent yes; residualControl { U 1e-4; p 1e-4; "(k|epsilon)" 1e-4; } } potentialFlow { nNonOrthogonalCorrectors 10; } relaxationFactors { equations { U 0.9; k 0.7; epsilon 0.7; } } cache { grad(U); } fvSchemes: Code:
ddtSchemes { default steadyState; } gradSchemes { default Gauss linear; grad(U) cellLimited Gauss linear 1; } divSchemes { default none; div(phi,U) bounded Gauss linearUpwindV grad(U); div(phi,k) bounded Gauss upwind; div(phi,epsilon) bounded Gauss upwind; div((nuEff*dev2(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear corrected; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } wallDist { method meshWave; } |
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May 1, 2019, 15:18 |
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#2 |
New Member
jawahar sivabharathy
Join Date: Jan 2011
Posts: 12
Rep Power: 15 |
Hi Jinjolee,
What is the Reynolds number and what geometry are you computing the flow for? |
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May 1, 2019, 15:44 |
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#3 | |
Member
Joe lee
Join Date: Nov 2018
Posts: 59
Rep Power: 8 |
Quote:
My geometry is a cyclist riding on a bike(as shown in the figure below). And I am measuring for the air drag from the external flow with inlet velocity of 12.5m/s, so if I am correct(sorry for my poor fluid background), the Reynolds number should be: (12.5*1.638)/(1.5*e-5) = 1365000 where 1.638 is the wheelbase length of the bike(I take it as characteristic length) Thanks. |
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October 25, 2019, 22:09 |
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#4 |
New Member
Igor Leonardo
Join Date: Jul 2016
Location: Brazil - SP - SJC
Posts: 20
Rep Power: 10 |
Hello Jinjolee,
Im facing similar issue. Did you manage to solve your problem? |
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Tags |
convergence, residual, simplefoam, steady-state, transient |
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