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Valle September 23, 2009 11:37

Velocity gradient manipulation
Hello everyone,

in order to get on the OpenFoam software, I calculated an example from an industrial task with CFX and OpenFoam (simpleFoam). I tired to choose all BC to be equal (discretization, turbulence model, mesh, time step, etc.). The results were very interesting, because on the one hand the integral flow field in the domain was nearly the same, but on the other hand local differences in the flow field occured, which I try to understand now. The main differences were divergent velocity gradients in regions of a direction change and in regions where a secondary flow (as a results of the direction change) was present. So I varried nearly all numerical parameters in OpenFoam (discretization, non-orth. correctors, dT, relaxation factors, etc.) in order to understand if it is influenced by the numerical adjustment or maybe it is something different. My result was, when the flow field stabilzed (converged) during the calculation, that every change of the numerical parameters affected the flow field only in a negligible manner, even the discretization scheme for the convection. This was really surprising.
My question is now, has someone experience in manipulating the flow field (especially the gradient calculation/ treatment) in OpenFoam by using the numerical parameters, or has someone an idea where this divergence might come from?

P.S I calculated the same problem with FLUENT, the results were identical to the results of CFX, especially regarding to the velocity gradient calculation.

Kind regards


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