Dear all,

we had a discussion today in the CFD team in our department and I mentioned that it is usually not necessary to require a user to define boundary conditions for turbulence quantities on or in the vicinity of walls.

Usually, wall velocity and heat flux and/or temperature are sufficient.

Physical considerations or model equations require a certain value or asymptotic behavior of turbulence quantities such as turbulent kinetic energy, turbulent frequency or dissipation at or close to the wall. Therefore, you can either implement a fixed value on the wall (such as turbulent kinetic energy = 0) or set a solution dependent value in the cell center of a wall-bounded cell (which requires that you can identify these cells) and adjust the contributions of these faces or volumes to the matrix coefficients directly.

At least, that is how I remember we did it in our code at university.

In OpenFOAM® you can or have to define wall values, and correctly setting k=0 does not even work.

Any comments? Maybe this has already been discussed on www.cfd-online.com. I posted this thread there also today.

Best regards, Ulf.

Dear Ulf,

I agree that setting those boundary conditions are a bit strange. How to set the wall values depends on the implementation of the wall treatment, which it is difficult for the user to know anything about. Before there was an alternative to specify the boundary conditions on a higher level, as physicalType, in the boundary file. Then FoamX took care of setting the lower-level boundary condition in the time directories. That was in fact the only useful thing with FoamX. I don't know if something similar is available today, but I doubt it.

Best regards,
Håkan