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Rough wave boundary layer

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Old   February 15, 2019, 05:04
Default Rough wave boundary layer
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Dora
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Dear Foamers,

I am trying to use interFoam to compute the wave-induced bed shear stress on rough bed. The problem is that I need very fine mesh near the bed ( in order of 0.2 mm) to capture the wave boundary layer.

In case of smooth bed, this doesn't represent an issue . In this case interFoam results is in very good agreement with the experimental measurements for both laminar and turbulent conditions.

The problem is when I am trying to model the rough bed. Then only way I could find to represent the surface roughness in OpenFOAM is by using one of the rough wall function (nutkRoughWallFunction or nutURoughWallFunction.

When using this wall function at the beginning I noticed that the modeled bed shear stress is an order of magnitude smaller than the experimental values. Then I realized that at this mesh resolution, the rough wall function will not include the effect of the roughness since this require Y+ to be in order of 30. Actually this raise a question also regarding the validity of using a wall function for such fine mesh near the wall (Y+ in order of 1). I also discovered that the resulting bed shear stress is highly mesh dependent( increases when Y+ increase)

So my question is, how I can model this rough surface in turbulent flow while preserving the mesh resolution?

Any help is highly appreciated

Kind regards
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shear stress, turbule model, wall functions, wave boundary conditions

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