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-   -   Convergence....... (http://www.cfd-online.com/Forums/fluent/28385-convergence.html)

Oliver March 29, 2001 19:10

Convergence.......
 
Hello all,

I am modeling the nose section and cooling ducts of a racing car.

The solution converges well in laminar flow, however when i run turbulence in the model (standard k-e) the turbulence terms (k and e) ossilate and diverge. I tried adjusting under-relaxation factors but to no avail.

In fluent I get the following message before each iteration: "Turbulence viscosity is limited to viscosity ratio of 1x10^5 in 1000 [example] cells".

What does this message mean?

How can I overcome this problem?

Could my mesh be at fault?

Thanks for your help. Oliver


hvn March 30, 2001 02:37

Re: Convergence.......
 
Increase to 10^6 the turbulence viscosity. There is a panel where there are maximum value for differents variables.

Flav March 30, 2001 07:00

Re: Convergence.......
 
First of all, try to see where the turbulent viscosity ratio is limited to 1e5 (Surface/Iso-surface/Turb Viscosity Ratio=1e5). Maybe the cells are not good quality in that region. Check the mesh.

Anyway, increasing the turbulent viscosity ratio to 1e6 will not help the residuals convergence. I suggest you try another initialization instead. What I mean is that you can specify other values for k and epsilon when you initialize the domain.

I sometimes get the warning message about the turbulent viscosity ratio. The number of cells concerned usually increases, and then decreases until no cell reaches the ratio limit.



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