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How could I specify the value or formula of turbulent k on the wall?

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Old   May 24, 2013, 11:38
Default How could I specify the value or formula of turbulent k on the wall?
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Dear everyone,

I wish to compute the external flow over a blunt body such as a cylinder or some, using the k-e with wall functions or the k-w SST. I followed the setting-up way in many literatures. But I couldn't get a satisfactory drag or lift force.

After checking the model with caution, I found that in the literatures they specified the value of k on the wall, which is, to give a Diriclet boundary for the equation. For example, some can specify the k as u*^2/sqrt(Cmu), which is, to force the local equilibrium on the wall. Or some can give a zero k on the wall.

But, in fluent, the k value would be directly solved from the k-equation, throughout the whole field including the near-wall meshes, which I guess may be a major difference between my model and those in the papers.

I know that the epsilon near the wall was derived from the local equilibrium on the wall, in which the k was also presumed. But in the fluent, only the epsilon was introduced in the near-wall function or treatment. I wonder whether this is a deviation from the local equilibrium assumption?

I know that the k-value could be specified or the formula be included in the near-wall treatment in Flow-3d and Openfoam, but I do not have time to start with these softwares. I really wonder whether I could achieve that in fluent.

Very apologized that I'd post a similar thread in the UDF board. But I didn't get replied after my last post. I guess that may be less noticed because in the sub-board. But I wish to say this is not a duplication of that thread. If this similar thread is not allowed in the forum, pls everybody or the Administrator remind me in time. Many thx !!

my that thread in the UDF board
The comparison of the k value near the wall by the fluent and the formula was also depicted in my last post there.

And I really appreciate the reply by blackmask there.

Many thanks to everybody!!
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