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INCOHERENT RESULTS USING PIMPLE (PISO MODE) solver |
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#1 | |
New Member
Angel Garcia
Join Date: Apr 2020
Posts: 4
Rep Power: 6 ![]() |
Dear foamers,
I'm working on a Blade-Vortex incidence simulation (LES). As usual, I need a reference situation to compare BVI effects which obviously is the flow around the chosen airfoil (SD7003). The case is assumed incompressible, with Re=60000. My mesh is all generated using blockMesh, with y+~0.3. Using checkMesh utility gives me the following result (I think it is a good mesh): Quote:
I have tried changing time schemes (crank-Nicholson, backwards and even first order),space schemes, pimple parameters, orthogonal correctors and finally, I have tested a 2D case, but problems remains the same. I did not try to change my mesh because I think is ok...The folder case is also attached. Due to size limitation I'm not able to upload log.pimplefoam file, but I can send it via email.residuals.png coef_cd.pdf coef_cl.pdf mesh_1.jpg SD7003.zip Any suggestions? Thanks a lot to all community members, this forum is really useful! Best regards, Ángel. |
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#2 |
Senior Member
Join Date: Apr 2020
Location: UK
Posts: 711
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Just a few quick observations, since I am afraid that I haven't dug into your zip files. If you are after a steady state set of lift & drag coeffs, why not take advantage of the PIMPLE algorithm and run with a much larger time step - ie Co > 1? You'll get to your steady solution far more quickly then.
Other points: OpenFOAM has very little numerical damping cf commercial CFD codes, and so with a fine mesh and a small time step your hi Re solution will probably show instability that may be causing the solver to work hard. Alternatively, are your tolerances too tight? Take a look at the run log output and see what it is doing each time step. Finally - I am not sure how you are calculating your coeffs, but do keep in mind that the pressure "p" in the incompressible solvers is kinematic pressure, i.e. is actually p/rho. That will affect the values, but of course won't flip the sign on t he drag. It's probably worth just examining the pressure field in paraView and then doing a handcalculation estimate for the coeffs to check that your coeff calculation is doing what you think it should be doing. Good luck! |
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#3 |
New Member
Angel Garcia
Join Date: Apr 2020
Posts: 4
Rep Power: 6 ![]() |
Dear Tobermory,
First of all, thanks for your reply. I think you are right, for this reference case, I could use PIMPLE. However, when I tried it seems to be slower than PISO due to internal loops, but I will try again. Talking about tolerance, I have attached fvSolution and fvSchemes files. I increased pressure tolerance in order to reduce residual. I will see pressure distribution in Paraview as you have said. Thank you so much for your time! |
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#4 |
New Member
Angel Garcia
Join Date: Apr 2020
Posts: 4
Rep Power: 6 ![]() |
fvSchemes code:
Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: v1912 | | \\ / A nd | Website: www.openfoam.com | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; location "system"; object fvSchemes; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // ddtSchemes { default backward; } d2dt2Schemes { } gradSchemes { default Gauss linear; grad(nuTilda) cellLimited Gauss linear 1; grad(U) cellLimited Gauss linear 1; } divSchemes { default Gauss limitedLinear; div(phi,U) Gauss linear; div(phi,k) Gauss limitedLinear 1; div(phi,B) Gauss limitedLinear 1; div(B) Gauss linear; div(phi,nuTilda) Gauss limitedLinear 1; div((nuEff*dev2(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear limited 0.33; } interpolationSchemes { default linear; } snGradSchemes { default limited 0.33; } wallDist { method meshWave; } // ************************************************************************* // Code:
/*--------------------------------*- C++ -*----------------------------------*\ | ========= | | | \\ / F ield | OpenFOAM: The Open Source CFD Toolbox | | \\ / O peration | Version: v1912 | | \\ / A nd | Website: www.openfoam.com | | \\/ M anipulation | | \*---------------------------------------------------------------------------*/ FoamFile { version 2.0; format ascii; class dictionary; location "system"; object fvSolution; } // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // solvers { p { solver GAMG; tolerance 1e-7; relTol 0.001; smoother GaussSeidel; nCellsInCoarsestLevel 50; } pFinal { $p; relTol 0; // Explicit specify solver for coarse-level correction to override // solution tolerance coarsestLevelCorr { solver PCG; preconditioner DIC; relTol 0.001; } } "(U|k|B|nuTilda)" { solver smoothSolver; smoother symGaussSeidel; tolerance 1e-6; relTol 0; } UFinal { $U; tolerance 1e-05; relTol 0; } kFinal { $k; tolerance 1e-05; relTol 0; } } PIMPLE { nCorrectors 3; nOuterCorrectors 1; nNonOrthogonalCorrectors 1; pRefCell 1001; pRefValue 0; } // ************************************************************************* // Last edited by angatri_14; July 19, 2020 at 07:04. |
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