ask

September 30, 2001, 11:10

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

October 4, 2001, 02:47

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

October 4, 2001, 03:00

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

Sincerely, Jinwook

October 5, 2001, 02:35

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

October 10, 2001, 13:16

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.

September 30, 2001, 11:10	ask	#1
lucy Guest Posts: n/a	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

October 4, 2001, 02:47	Re: ask	#2
Jin-Wook LEE Guest Posts: n/a	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

October 4, 2001, 03:00	Re: ask	#3
Jin-Wook LEE Guest Posts: n/a	Sorry, it's 'turbulent visocisity to laminar(molecular) viscosity'(= Mu_t / Mu_l). Sincerely, Jinwook

October 5, 2001, 02:35	Re: ask	#4
Tae Sang Park Guest Posts: n/a	Check if you scale your grid !! Sometimes I get the message when I don't scale the grid made by millimeter to meter.

October 10, 2001, 13:16	Re: ask	#5
DA Guest Posts: n/a	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.