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Different flow pattern between OpenFOAM and CFX |
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January 12, 2010, 07:08 |
Different flow pattern between OpenFOAM and CFX
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Join Date: Sep 2009
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Dear Foamers,
I'd like to validate OpenFOAM by using CFX. I use the same mesh and boundary conditions in both software. The same Reynolds number of 300,000. The LES Smagorinsky in CFX using the default damping function (with Cs=0.1) and Scalable as wall function; The LES Smagorinsky in OpenFOAM is shown as: LESModel Smagorinsky; delta cubeRootVol; printCoeffs on; cubeRootVolCoeffs { deltaCoeff 1; } vanDriestCoeffs { delta cubeRootVol; cubeRootVolCoeffs { deltaCoeff 1; } smoothCoeffs { delta cubeRootVol; cubeRootVolCoeffs { deltaCoeff 1; } maxDeltaRatio 1.1; } Aplus 26; Cdelta 0.158; } smoothCoeffs { delta cubeRootVol; cubeRootVolCoeffs } Where can I modify the Cs in OpenFOAM? Moreover, I don't use any wall functions. The inlet used in CFX is: Normal Speed 1m/s The inlet used in OpenFOAM is: INLET { type turbulentInlet; fluctuationScale (0.01 0.01 0.01); referenceField uniform (1 0 0); alpha 0.1; value uniform (1 0 0); } I created a cyclic patch in OpenFOAM to match the periodic BC of CFX. I set pointSync to false and matchTolerance to 0.2. Regarding the discretiztion schemes: in CFX: Advection Scheme: Central Difference. Transient Scheme: Second Order Backward Euler in OpenFOAM: ddtScheme: backward others: Gauss linear The flow pattern is not the same: in CFX, no separation occurs on the top of the cylinder, which is good for a Reynolds number of 300,000.However, in OpenFOAM, a separation with no reattachment can be seen as if the Reynolds number was less enough from 300,000. I do not know where this difference can come from. If anyone see something I should change in my setting, it would be great . Thanks a lot, AirS. |
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