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Old   March 21, 2012, 15:46
Default K-Omega Model
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pooyan
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Hi All,

I am simulating incompressible turbulent flow over a flat plate using OpenFoam. I am doing RANS simulation and I have selected k-omega turbulence model. I want to get the profile of U+ vs. y+ and validate it with theory. For my simulation, I do not want to use any wall function and I am using pisoFoam transiet solver available in OpenFoam. my problem is that the convergence when not using wall function is so slow and I should use a very small time step for stable solution. has anyone else faced this convergence issue before?!
Besides, I have some problems with steasy solver " simpleFoam ". I use the same fvSchemes and fvSolution as one exists in tutorial for k-omega sst model, but the solution will be wrong this way. Do you have any idea how I can find the right schemes for k-omega model for steady state simulation?!

I have attached the B.C for my problem.

Thanks,
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Old   March 22, 2012, 03:59
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Quote:
Originally Posted by sam1364 View Post
Hi All,

I am simulating incompressible turbulent flow over a flat plate using OpenFoam. I am doing RANS simulation and I have selected k-omega turbulence model. I want to get the profile of U+ vs. y+ and validate it with theory. For my simulation, I do not want to use any wall function and I am using pisoFoam transiet solver available in OpenFoam. my problem is that the convergence when not using wall function is so slow and I should use a very small time step for stable solution. has anyone else faced this convergence issue before?!
Besides, I have some problems with steasy solver " simpleFoam ". I use the same fvSchemes and fvSolution as one exists in tutorial for k-omega sst model, but the solution will be wrong this way. Do you have any idea how I can find the right schemes for k-omega model for steady state simulation?!

I have attached the B.C for my problem.

Thanks,
Why do you use an outlet at the top boundary. I think I would use something similar to a symmetry plane at this one as well. or if you use an outlet there I would use a pressure condition that is similar to total pressure, like an atmosphere.

The solution should be steady after a while, therefore a steady solver like simpleFoam should be sufficient, except you want to simulate developing flow.

The omega wall function is not a real wall function, it is a continuous wall function. You should probably use it for omega at the wall. Did you make sure your y+<1, since you are not using any wall functions? Additionally, if you use a cell gradient towards the wall, make sure that it is very smooth, such as an expansion/growth factor of 1.1 or 1.2. k-omega-SST in OF seems to be sensitive to this.
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