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June 5, 2012, 12:27 
Ansys/Fluent and OpenFoam comparison, LES, XiFoam, Smagorinsky

#1 
Member
achinta
Join Date: May 2010
Location: Sydney
Posts: 66
Rep Power: 8 
Hi All,
I would to compare results of Fluent and OpenFoam for Cold simulation of EV burner. In Fluent, the simulation was done using SmagorinskyLilly 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 OFb=1c) 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 Last edited by achinta; June 5, 2012 at 12:32. Reason: improvement 

June 7, 2012, 10:15 
may be able to help

#2 
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cant say
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Hey 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 

June 7, 2012, 11:25 
again

#3 
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Hi 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 

June 8, 2012, 11:08 

#4 
Member
achinta
Join Date: May 2010
Location: Sydney
Posts: 66
Rep Power: 8 
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 .. 

June 8, 2012, 11:28 

#5 
Member
achinta
Join Date: May 2010
Location: Sydney
Posts: 66
Rep Power: 8 
Hello everyone,
I am simulating cold combustion . it diverged. Please tell me if i made any mistake. Kind regards, Achinta Last edited by achinta; June 23, 2012 at 14:21. 

June 11, 2012, 12:48 

#6 
Member
achinta
Join Date: May 2010
Location: Sydney
Posts: 66
Rep Power: 8 
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((1A(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 1e06; relTol 0.1; } pFinal { solver PCG; preconditioner DIC; tolerance 1e06; relTol 0; } U { solver PBiCG; preconditioner DILU; tolerance 1e05; relTol 0; } k { solver PBiCG; preconditioner DILU; tolerance 1e05; relTol 0; } B { solver PBiCG; preconditioner DILU; tolerance 1e05; relTol 0; } nuTilda { solver PBiCG; preconditioner DILU; tolerance 1e05; 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 1e6; relTol 0.1; smoother GaussSeidel; nPreSweeps 0; nPostSweeps 2; nFinestSweeps 2; cacheAgglomeration true; nCellsInCoarsestLevel 0; agglomerator faceAreaPair; mergeLevels 1; }; pFinal { solver GAMG; tolerance 1e7; relTol 0; smoother GaussSeidel; nPreSweeps 0; nPostSweeps 2; nFinestSweeps 2; cacheAgglomeration true; nCellsInCoarsestLevel 0; agglomerator faceAreaPair; mergeLevels 1; }; U { solver PBiCG; preconditioner DILU; tolerance 1e06; relTol 0; } k { solver PBiCG; preconditioner DILU; tolerance 1e06; relTol 0; } B { solver PBiCG; preconditioner DILU; tolerance 1e06; relTol 0; } nuTilda { solver PBiCG; preconditioner DILU; tolerance 1e06; 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 Last edited by achinta; June 11, 2012 at 15:39. Reason: improvement 

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