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- - **Ansys/Fluent and OpenFoam comparison, LES, XiFoam, Smagorinsky**
(*http://www.cfd-online.com/Forums/openfoam/102886-ansys-fluent-openfoam-comparison-les-xifoam-smagorinsky.html*)

Ansys/Fluent and OpenFoam comparison, LES, XiFoam, SmagorinskyHi All,
I would to compare results of Fluent and OpenFoam for Cold simulation of EV burner. In Fluent, the simulation was done using Smagorinsky-Lilly model. I would like to compare it with Smagorinsky model of OpenFoam. I have boundary conditions given for Fluent and I need to convert it to OpenFOAM input. Could someone give me hints about conversion. I have the follwing parameters for ANSYS and I need equivalent parameters for OpenFOAM (if it exists): 1)critical rate of strain 2)progress variable (I think its regress variable in OF---b=1-c) 3)mean mixture fraction 4)Mean fraction variance 5)Constants of Smagorinsky model-- Cs, Cfvar,PDF Schmidt number 6)Turbulent length scale constant 7) Turbulent flame speed constant 8)Stretch Factor coefficient 9)Turbulent Schmidt number Btw, 1) Do I have to change /constant/LESProperties file for a given problem? 2) Do I have to change anything except nu in constant/transportProperties file? P.S: My next step would be to compare combustion simulation of ANSYS and XiFoam. I might need some help there too :) Kind regards, Achinta |

may be able to helpHey Achinta,
Actually I am new here and also to the field of OpenFOAM, Combustion and LES, which is the reason why I am writing this. I need some problems, just to practice and I think you can provide me with one here. If your geometry and the FLUENT case/data files are not confidential, I would request you to send it over to me at turbulentreactingflows@gmail.com First we should go only after LES (cold flow) and then Combustion with LES using OpenFOAM. I can't promise anything at the moment but will try to help as long as time permits. Lets get started, cheers |

againHi again Achinta,
I feel that the tone of my previous post was not quite pleasant. I am really sorry for that. Basically the point is that if you can send me your ANSYS FLUENT case (for BC's) files then I may be able to help you with OpenFOAM (both LES alone and LES with Combustion). I hope it will benefit both of us cheers |

Hi there,
Sorry for late reply. I was bit busy. I am working for a company and the mesh file is confidential. Sorry, i cannot send you those files. I am new to LES too and i dont have any extra tutorials. please send me some if you have :).. |

Hello everyone,
I am simulating cold combustion . it diverged. Please tell me if i made any mistake. Kind regards, Achinta |

Hello everyone,
I am able to set boundary conditions and run the code. But it diverges after 15 time steps. I had used the following schemes: ----- ddtSchemes { default backward; } gradSchemes { default Gauss linear; grad(p) Gauss linear; grad(U) Gauss linear; } divSchemes { default none; div(phi,U) Gauss Linear; div(phi,k) Gauss limitedLinear 1; div(phi,B) Gauss limitedLinear 1; div(phi,nuTilda) Gauss limitedLinear 1; div(B) Gauss linear; div((nuEff*dev(T(grad(U))))) Gauss linear; } laplacianSchemes { default none; laplacian(nuEff,U) Gauss linear corrected; laplacian((1|A(U)),p) Gauss linear corrected; laplacian(DkEff,k) Gauss linear corrected; laplacian(DBEff,B) Gauss linear corrected; laplacian(DnuTildaEff,nuTilda) Gauss linear corrected; } interpolationSchemes { default linear; interpolate(U) linear; } snGradSchemes { default corrected; } fluxRequired { default no; p ; } ----- here is fvSolution file: ------ p { solver PCG; preconditioner DIC; tolerance 1e-06; relTol 0.1; } pFinal { solver PCG; preconditioner DIC; tolerance 1e-06; relTol 0; } U { solver PBiCG; preconditioner DILU; tolerance 1e-05; relTol 0; } k { solver PBiCG; preconditioner DILU; tolerance 1e-05; relTol 0; } B { solver PBiCG; preconditioner DILU; tolerance 1e-05; relTol 0; } nuTilda { solver PBiCG; preconditioner DILU; tolerance 1e-05; relTol 0; } } PISO { nCorrectors 2; nNonOrthogonalCorrectors 0; } ------------- With the above settings and time step of 1micro second, the solution diverged in 15 time steps. 1) I refered some threads which suggested to use 'filteredLinear' for convective schemes. So I changed "div(phi,U) Gauss filteredLinear;" (Should I change other divergence schemes too?) 2) Some threads suggested GAMG for p and pFinal. I made some changes in tolerance limits too. here is the file: -------- p { solver GAMG; tolerance 1e-6; relTol 0.1; smoother GaussSeidel; nPreSweeps 0; nPostSweeps 2; nFinestSweeps 2; cacheAgglomeration true; nCellsInCoarsestLevel 0; agglomerator faceAreaPair; mergeLevels 1; }; pFinal { solver GAMG; tolerance 1e-7; relTol 0; smoother GaussSeidel; nPreSweeps 0; nPostSweeps 2; nFinestSweeps 2; cacheAgglomeration true; nCellsInCoarsestLevel 0; agglomerator faceAreaPair; mergeLevels 1; }; U { solver PBiCG; preconditioner DILU; tolerance 1e-06; relTol 0; } k { solver PBiCG; preconditioner DILU; tolerance 1e-06; relTol 0; } B { solver PBiCG; preconditioner DILU; tolerance 1e-06; relTol 0; } nuTilda { solver PBiCG; preconditioner DILU; tolerance 1e-06; relTol 0; } } PISO { nCorrectors 3; nNonOrthogonalCorrectors 1; } ----- I increased time step to 5 microseconds since there are many corrector loops. But the problem still exists and the solution is diverging. I kindly request someone with LES experience to help me out. What could be the reason? Is it because of Smagorinsky model? Should I use OneEqEddy LES model? Or is it because of Boundary/ initial conditions? Should i use a smaller time step? The mesh is really fine (6 million cells) and uses hexahedral and tetrahedral cells. I am using pisoFoam (transient calculations. So its bit tricky). Should i use pimple instead of piso? Regards, Achinta |

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