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-   -   Converging then Diverging Residuals??? (http://www.cfd-online.com/Forums/fluent/42338-converging-then-diverging-residuals.html)

Erika Johnson September 19, 2006 07:24

Converging then Diverging Residuals???
 
Hello,

I was wondering if anyone has ever had any experience with residuals that intially start to converge and then after several iterations (i.e. 25,000+), they start to diverege???

I am working with the Reynolds Stress Model and I have decent convergence (1e-05) on everything except continuity (1e-2). In trying to get continuity to converge I let the simulation run and now at 25,000+ iterations I'm noticing that my Reynolds stresses, y-velocity, k and epsilon are starting to diverge slowly...Is the simulation adjusting itself in order to get the continuity to converge???

If it helps at all I'm simulating a flat plate boundary layer with super super fine mesh and low freestream intensity (0.2%).

Any ideas???

Thanks so much, Erika

sam September 19, 2006 10:20

Re: Converging then Diverging Residuals???
 
It is normal dont worry

Erika Johnson September 19, 2006 10:24

Re: Converging then Diverging Residuals???
 
So then should I allow the solution to progress??? Will it eventually converge???

sam September 19, 2006 10:27

Re: Converging then Diverging Residuals???
 
yes. But not in absolute terms. It may start fluactuating between some value i.e diverging and converging. check the mass flow balance(it is ur gloval convergence)

Erika Johnson September 19, 2006 10:30

Re: Converging then Diverging Residuals???
 
Thanks for your help!

sam September 19, 2006 10:32

Re: Converging then Diverging Residuals???
 
wats ur msn or yahoo id?

Erika Johnson September 19, 2006 10:35

Re: Converging then Diverging Residuals???
 
I don't have one.

sam September 19, 2006 10:37

Re: Converging then Diverging Residuals???
 
which type of flow u r working on

Erika Johnson September 19, 2006 10:45

Re: Converging then Diverging Residuals???
 
I'm simulating a boundary layer experiment that was conducted in a wind tunnel with very low free stream turbulence intensity (0.02%). I'm actually trying to duplicate the turbulence intensity curves that Klebanoff published in his experiment from 1955 (Characteristics of Turbulence in a Boundary layer with Zero Pressure Gradient).


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