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lucy September 30, 2001 11:10

ask
 
Hello everyone, During I calculate,I get the message of "turblent viscosity limited to viscosity ratio of 1.000000e+5 in 2097 cells" for each iterate. Does anybody know what this means?

Thank you very much

Jin-Wook LEE October 4, 2001 02:47

Re: ask
 
It means the ratio of 'laminar(molecular) viscosity to turbulent visocisity' exceeds pre-scribed limit, 1.e+05. You can see the limit at the 'Solve --> Control --> Limits' panel.

As far as mt experienced is concerned, the ratio for general fluid flow is larger than O(10^2) and less than O(10^4). That's why the limit is set to 10^5. I've met such situation when very strong shear exists in the very large geometry. Please discuss with whom he is specialists for turbulent flow whether the large value of the ratio for your problem is reasonable or not. If you think that the ratio may be larger than 10^5 for your problem, then you can simply change the limit to the larger value and you do not see the message.

Sincerely, Jinwook


Jin-Wook LEE October 4, 2001 03:00

Re: ask
 
Sorry, it's 'turbulent visocisity to laminar(molecular) viscosity'(= Mu_t / Mu_l).

Sincerely, Jinwook


Tae Sang Park October 5, 2001 02:35

Re: ask
 
Check if you scale your grid !! Sometimes I get the message when I don't scale the grid made by millimeter to meter.

DA October 10, 2001 13:16

Re: ask
 
Normally when I've seen this something is wrong somewhere. If it's not the setup, it will probably be the grid; I've seen this with bad quality grids. If your skew is high, it is well worth remeshing rather than trying to fight the 'viscosity ratio > ' thing. A few more cells might take longer to iterate but you'll get to your solution far quicker in the end.


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