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Old   July 11, 2005, 11:56
Default roughness and y+ constraints
  #1
Jean
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Hi,

I am modeling an atmospheric boundary layer flow and I have a wall roughness of 1.6m I have a 2D domain of 1000m height. I meshed with a cell height of 4m, but I still have a viscosity ratio problem and my y+ is around 10000. If I refine my mesh to get smaller y+ going down to a cell height of 2m near the wall, my roughness height will exceed the center of my cell adjacent to the wall. I am using wall function k-epsilon.

Please help

Thank you
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Old   July 12, 2005, 09:54
Default Re: roughness and y+ constraints
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Razvan
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Change your turbulence model to SST-kw. If this does not solve the problem, change some settings for multigrid:

- set presweeps=postsweeps=2 - set pressure and all momentum to F-cycle - set turbulence quantities to V-cycle

If this will not solve the problem, then I do not know what else you can do.

Hope this will help you.

Best wishes, Razvan
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Old   July 12, 2005, 13:35
Default Re: roughness and y+ constraints
  #3
Jean
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Thx Razwan,

I am modeling wind turbine effect on the atmospheric layer. Is the k-w convenient for such a problem?

The domain is rectangular. I chose a velocity inlet, an outflow and a symmetry boundary for the top of the domain at 1km height. Do you think those boundaries are convenient?

Thank you
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Old   July 14, 2005, 03:44
Default Re: roughness and y+ constraints
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Razvan
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Not k-w but SST-kw. You should better change the "outflow" boundary to "pressure-outlet" with outlet pressure value=local(desired) atmospheric pressure. If you are modeling wind turbine then I think 1km might be too much. I am not experienced in this tipe of situation, but I don't see no problem in lowering it to say, 150-200m top. That should be enough. Of course, if you are interested in high winds also, this could be an explanaition for a such big domain you have chosen.

Best wishes, Razvan
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