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B.C's for k and omega

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Old   January 11, 2002, 17:34
Default B.C's for k and omega
  #1
Suppe
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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!
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Old   January 11, 2002, 18:06
Default Re: B.C's for k and omega
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Jonas Larsson
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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).
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Old   January 11, 2002, 19:21
Default Re: B.C's for k and omega
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Suppe
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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!
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Old   January 12, 2002, 05:41
Default Re: B.C's for k and omega
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Jonas Larsson
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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.
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Old   January 12, 2002, 12:16
Default Re: B.C's for k and omega
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Suppe
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That's a good suggestion. Thanks again for your reply.
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Old   January 14, 2002, 11:18
Default Re: B.C's for k and omega
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Dennis
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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/
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