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#1 |
New Member
John
Join Date: Mar 2019
Posts: 26
Rep Power: 7 ![]() |
Hi,all Foamers
I'm running a simulation about bubble rising using MPPICInterFoam solver, coupling LPT to VOF method . Everything is going well when i test with a simple domain . But when i tried it with a real domain about 90000 hexahedra of cells, It freezing at time step 4.503 because of the value of Courant number is so high , about XX e+12 . I tried to decrease the deltaT in the ControlDict to be 1e-8 even 1e-9 but it still not work. But when i decrease the number of cell from 90000->11250 . It worked well. So, what is the problem ? How i can run this simulation at 90000 cell . I attached my fvSolution, fvSchemes and checkMesh belowed. Any help would be highly appreciated , Thank you so much for reading ! checkMesh Code:
Mesh stats points: 97061 faces: 276900 internal faces: 263100 cells: 90000 faces per cell: 6 boundary patches: 3 point zones: 0 face zones: 0 cell zones: 0 Overall number of cells of each type: hexahedra: 90000 prisms: 0 wedges: 0 pyramids: 0 tet wedges: 0 tetrahedra: 0 polyhedra: 0 Checking topology... Boundary definition OK. Cell to face addressing OK. Point usage OK. Upper triangular ordering OK. Face vertices OK. Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces... Patch Faces Points Surface topology inlet 36 49 ok (non-closed singly connected) outlet 900 961 ok (non-closed singly connected) walls 12864 12936 ok (non-closed singly connected) Checking geometry... Overall domain bounding box (-0.075 -0.075 0) (0.075 0.075 0.5) Mesh has 3 geometric (non-empty/wedge) directions (1 1 1) Mesh has 3 solution (non-empty) directions (1 1 1) Boundary openness (-1.25066e-16 -1.31008e-17 1.48292e-18) OK. Max cell openness = 1.35525e-16 OK. Max aspect ratio = 1 OK. Minimum face area = 2.5e-05. Maximum face area = 2.5e-05. Face area magnitu des OK. Min volume = 1.25e-07. Max volume = 1.25e-07. Total volume = 0.01125. Cell volumes OK. Mesh non-orthogonality Max: 0 average: 0 Non-orthogonality check OK. Face pyramids OK. Max skewness = 1.11023e-13 OK. Coupled point location match (average 0) OK. Mesh OK. Code:
ddtSchemes { default Euler; } gradSchemes { default Gauss linear; } divSchemes { default none; div(rhoPhi,U) Gauss upwind; div(phi,alpha) Gauss vanLeer; div(phirb,alpha) Gauss linear; div(alphaRhoPhic,k) Gauss upwind; div(alphaRhoPhic,epsilon) Gauss upwind; div((((alphac*rho)*nuEff)*dev2(T(grad(U))))) Gauss linear; div(phiGByA,kinematicCloud:alpha) Gauss linear; } laplacianSchemes { default Gauss linear corrected; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } fluxRequired { default no; p_rgh; pcorr; alpha.water; } Code:
solvers { "alpha.water.*" { nAlphaCorr 2; nAlphaSubCycles 2; cAlpha 1; MULESCorr yes; nLimiterIter 2; solver smoothSolver; smoother symGaussSeidel; tolerance 1e-7; relTol 0; maxIter 100; } pcorr { solver PCG; preconditioner DIC; tolerance 1e-5; relTol 0; } p_rgh { solver PCG; preconditioner DIC; tolerance 1e-07; relTol 0.05; } p_rghFinal { $p_rgh; relTol 0; } "(U|k|epsilon).*" { solver smoothSolver; smoother symGaussSeidel; tolerance 1e-06; relTol 0; } kinematicCloud:alpha { solver GAMG; tolerance 1e-06; relTol 0.1; smoother GaussSeidel; cacheAgglomeration true; nCellsInCoarsestLevel 10; agglomerator faceAreaPair; mergeLevels 1; } } PIMPLE { momentumPredictor no; nOuterCorrectors 1; nCorrectors 2; nNonOrthogonalCorrectors 2; pRefCell 0; pRefValue 0; residualControl { "(p|U)" { tolerance 1e-4; relTol 0; } } // convergence 1e-08; } relaxationFactors { fields { p 1; } equations { U 1; k 1; epsilon 0.5; R 0.5; nuTilda 0.5; omega 0.5; } } |
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#2 |
Senior Member
Robert
Join Date: May 2015
Location: Bremen, GER
Posts: 292
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If it works with larger cells, but not with your smaller mesh, its likely that your cells are just too small. Either go with a larger mesh or decrease your timestep until it works.
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#3 |
New Member
John
Join Date: Mar 2019
Posts: 26
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Thank you Robert for a kindly answer !
Actually when i try it with Euler-Euler solver with the same number of cells are 90000, it worked . But when i tried it with VOF solver , i didn't work . So i think may be the problem is not about the mesh . I tried to decreased the timestep even 1e-20 it still crashed . With adjustTimeStep (yes) it decreased like about 1e-30 . Do you have any idea i can look for solving this problem, Sir ! |
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#4 |
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Robert
Join Date: May 2015
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But VOF and adjustTimeStep works, as in does not crash, when the dT is decreased to ~ 1e-30?
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#5 |
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John
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Yes, sir . It works well but with 1e-30s deltaT time and my total time of simulation is 200s . It will take so so long for that simulation. Do you have any suggestion, Sir .
Thank you for still spending time for me ! |
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#6 | |
Senior Member
Robert
Join Date: May 2015
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Quote:
Co = ![]() you can see that there are indeed very few variables that influence Co. I would assume that you dont want to or can not change your velocity because you want to observe a certain process. So the only variables you can change are the mesh size ![]() ![]() If you want to keep your velocity and mesh resolution, you have to go with a timestep of 1e-30s. Want a larger timestep? Than you have to increase the mesh size. One more option: The more cells you have, the longer a simulation takes. Maybe you can consider reducing your overall domain size.
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