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K S Chang November 19, 2003 07:33

k-omega model and boundary layer
I want to validate the code in the turbulent boundary layer. The validation problem is referred in NPARC site.

My code is incompressbile, the scheme is hybrid, time is intergrated in the second order. The initial condition is freestream velocity and freestream turbulent quantities. And then, the results are compared.

In the plot of y+ and u+ , the velocity profile is underpredicted in log-law region. In viscos sublayer, the profile is agreement with the experimental data. The slope is same with the experimental data. However the C value is lower than data.

I don't know this region. k-eq. and omega-eq is discretized in hybrid scheme. Is this problem?? Or grid number is problem (y+_1 <= 1 settled) I have changed the frestream turbulent quantites, however the results is same.

If you konw this regions, let me know please.

In advance, thank you

Jonas Bredberg December 15, 2003 08:28

Re: k-omega model and boundary layer
Hi there,

Some k-omega models have problem with boundary layer flows, and especially deciding the freestream value of omega. I'm surprised that you didn't see an effect when changed the freestream omega. Papers by Menter, Kok and myself shows quite a large impact of the value for omega, if you use a standard Wilcox formulation of k-omega. If you use Menters, k-omega SST, or someother cross-diffusion modified omega-eq. you would probably have less dependency of the freestream omega. I would say that hybrid is good enough, but why not try shifting to van Leer or something else. Furthermore I would run a k-epsilon model as well, to check the measured data - you might not get good result, whichever model you use. A very rough wall would shift the log-law, and hence including friction could also help. Sorry that I couldn't help you more than this, however feel free to contact me,

Regards Jonas

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