low reynolds k omega / wall functions

stawrogin · November 25, 2009, 07:20

Hi,

I make my first steps with low-Reynolds models for heat transfer analysis.

When I understand the new wall function approach in OF 1.6. correctly, I “simply” can switch off the wall functions e.g. by using “calculated” in the nut-file and some reasonable bcs for omega and k at the walls. I build some test cases with grids of y+ below “1” and used fixed values for k (I used very low non-zero values) and zero gradient for omega. Does this make sense? But the convergence is quite poor and the results (e.g. when I estimate wallShear stresses from different models) differ strongly. Any hints or recommendations?
I also read that Fluent uses a low Reynolds correction for the k-omega model. Did anybody implement something like this in OF or compared the effect?

Thanks in advance

Stawrogin

Anne Lincke · March 30, 2011, 06:04

Hey Stawrogin,

" fixed values for k (I used very low non-zero values) and zero gradient for omega. Does this make sense?"

Fixed values for k which are non-zero but low are good but zero gradient for omega does not make sense.
Have a look at the post

http://www.cfd-online.com/Forums/ope...tml#post296705

November 25, 2009, 07:20	low reynolds k omega / wall functions	#1
stawrogin Member Join Date: Nov 2009 Posts: 36 Rep Power: 16	Hi, I make my first steps with low-Reynolds models for heat transfer analysis. When I understand the new wall function approach in OF 1.6. correctly, I “simply” can switch off the wall functions e.g. by using “calculated” in the nut-file and some reasonable bcs for omega and k at the walls. I build some test cases with grids of y+ below “1” and used fixed values for k (I used very low non-zero values) and zero gradient for omega. Does this make sense? But the convergence is quite poor and the results (e.g. when I estimate wallShear stresses from different models) differ strongly. Any hints or recommendations? I also read that Fluent uses a low Reynolds correction for the k-omega model. Did anybody implement something like this in OF or compared the effect? Thanks in advance Stawrogin

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March 30, 2011, 06:04		#2
Anne Lincke Senior Member Anne Gerdes Join Date: Aug 2010 Location: Hamburg Posts: 168 Rep Power: 15	Hey Stawrogin, " fixed values for k (I used very low non-zero values) and zero gradient for omega. Does this make sense?" Fixed values for k which are non-zero but low are good but zero gradient for omega does not make sense. Have a look at the post http://www.cfd-online.com/Forums/ope...tml#post296705