Hi all. I'm currently working on implementing Wilcox's k-w model in my flow solver (PNS based). I'm having a lot of problem with the wall boundary condition - I am working on supersoinc turbulent flow past a flat plate. I have used k=0 at the wall, but my problem seems to be with the omega b.c for the wall. Could anyone suggest some good references/ideas please? Thanks!

I don't have any references with me here but I struggeld lot with this myself several years ago... If I remember correctly Wilcox has a wall-roughness model which gives an omega value based on a surface roughness. Using this model, with a surface roughness set to something which is essentially "smooth" was the most stable and best boundary condition that I found. I think that this is also what Wilcox recommends - the wall-roughness model is surely described in his book (Turbulence Modeling for CFD).

I did look at Wilcox's wall-roughness condition, but I was wondering if there was any other b.c for a smooth wall. I think I'll try out the rough-wall b.c anyway. Thanks for your input!

If you set the surface roughness paramater (if I remember it correctly Wilcox calls it kr+ or something) to a value well inside the viscous sublayer, say 1, the wall will be smooth - I did a sensitivity analysis on this a long time ago and found that for flows over turbine blades 1 was certainly enough to get a "smooth" blade. It is quite easy for you also to half the kr+ paramater and run againg just to verify that you get the same result.

That's a good suggestion. Thanks again for your reply.

The following reference may be of interest to you.

Antti Hellsten: On the Solid-Wall Boundary Condition of omega in the k-omega-Type Turbulence Models, Technical Report, Helsinki University of Technology, Laboratory of Aerodynamics, Report B-50, Series B, 1998, ISBN 951-22-4005-X.

Available on-line from: http://aeropc5.hut.fi/~ahellste/