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simpleFoam for complicated geometry, nonorthogonal mesh, omega wall function 

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July 27, 2012, 06:00 
simpleFoam for complicated geometry, nonorthogonal mesh, omega wall function

#1 
Member
achinta
Join Date: May 2010
Location: Sydney
Posts: 66
Rep Power: 9 
Hello everyone,
I am using simpleFoam on complicated geometry (non orthogonal mesh). Here is the checkMesh report:  Mesh stats points: 6487723 faces: 19200050 internal faces: 18938278 cells: 6356388 boundary patches: 16 point zones: 0 face zones: 0 cell zones: 0 Overall number of cells of each type: hexahedra: 6356388 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). . . Mesh (nonempty, nonwedge) directions (1 1 1) Mesh (nonempty) directions (1 1 1) Boundary openness (9.64958e17 2.34786e15 6.13025e16) OK. Max cell openness = 4.58304e15 OK. Max aspect ratio = 299.485 OK. Minumum face area = 3.41806e11. Maximum face area = 0.000249108. Face area magnitudes OK. Min volume = 1.22828e14. Max volume = 4.16394e07. Total volume = 0.20005. Cell volumes OK. Mesh nonorthogonality Max: 87.0638 average: 19.2898 *Number of severely nonorthogonal faces: 18931. Nonorthogonality check OK. <<Writing 18931 nonorthogonal faces to set nonOrthoFaces Face pyramids OK. Max skewness = 2.88371 OK. Coupled point location match (average 0) OK. Mesh OK.  I am using SST turbulence model. I am using 'flowRateInletVelocity' for few inlets and it's mentioned like this: INLET { type flowRateInletVelocity; flowRate constant XXXX; // volume flow rate value uniform (0 0 0); } The boundary conditions for k and omega are:  Feature k, omega Turbulent inlet 0.4, 4000 Other inlets 1e6, 1e2 Walls type kqRWallFunction; type omegaWallFunction; value uniform 0.4; value uniform 4000; Outlet zeroGradient, zeroGradient internal field 0.4, 4000  I am using DICPCG for pressure, smoothSolver for omega and DILUPBiCG for others. My fvSchemes were as follows:  ddtSchemes { default steadyState; } gradSchemes { default Gauss linear; } divSchemes { default none; div(phi,U) Gauss linearUpwindV grad(U); div(phi,k) Gauss upwind; div(phi,omega) Gauss upwind; div((nuEff*dev(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear corrected; } interpolationSchemes { default linear; } snGradSchemes { default corrected; } fluxRequired { default no; p; }  The simulation diverges after 150 steps. I tried Gauss linear limited 0.333 for laplacian schemes which didn't work. gradSchemes was changed to 'cellLimited Gauss linear 1' and it was not good either. Could someone give me tips to improve the simulation? Note: When i use epsilonWallFunction(as wall boundary condition) for omega, it converges to some decent results (not accurate though) with the 1st set of fvSchemes. It's strange!! Kind regards, Achinta Last edited by achinta; July 27, 2012 at 06:07. Reason: typos 

October 20, 2013, 09:22 
how did u determine k and omega for complicated geometry

#2 
Senior Member
Hasan K.J.
Join Date: Dec 2011
Location: Bristol, United Kingdom
Posts: 199
Rep Power: 7 
Hey achinta,
I am stuck with similar problem but I'm a one step before u How did u determine the K and Omega for the complicated geometry, and did u over come the problem ? i am having the same problem Regards, Hasan. 

October 25, 2013, 00:58 
k and omega

#3  
Member
B T KANNAN
Join Date: Jul 2011
Location: CHENNAI (MADRAS), INDIA
Posts: 54
Rep Power: 7 
Quote:
Try to calculate k and epsilon from the intensity and velocity, which you know for inlet. If not, get it from experiments(available in literature). Then calculate omega by omega=epsilon/k  KANNAN 

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