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

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.:confused:

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
http://www.cfd-online.com/Forums/flu...near-wall.html
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!!