CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   FLUENT (http://www.cfd-online.com/Forums/fluent/)
-   -   convergence (http://www.cfd-online.com/Forums/fluent/39450-convergence.html)

vijay January 30, 2006 23:02

convergence
 
Hi,

I have a problem while running an unsteady case using coupled implicit scheme. The continuity and x,y,z velocity residuals are fluctuating between a constant minimum and maximum. They are going horizontally and parallely without converging. Does it mean that the grid should be refined further or is there something else to be done? Please suggest.

Thanks in advance

Muhammad Shakaib January 30, 2006 23:57

Re: convergence
 
you can try with smaller time steps

vijay January 31, 2006 01:46

Re: convergence
 
Hi,

Thanks for ur reply. But I tried with smaller time steps as well. Eventually after coming to the time step I required i.e. smaller time step multiplied with number of time steps, the fluctuations are starting again. Hope u have understood what I mean. Kindly suggest an alternative.

Thanks

Muhammad Shakaib January 31, 2006 06:29

Re: convergence
 
What type of fluctuation you have noticed. Typically there is convergence in 20-30 iterations for every time step i.e. residuals drop alteast an order of magnitude and if you have placed a surface monitor it becomes constant in these no. of iterations. Alongwith refining the grid you can test some more things; using different options of solution controls. Also use surface monitors to check whether convergence is acheived for each time step

HS January 31, 2006 08:35

Re: convergence
 
Are you sure the minimums and maximums are actually constant? I think the coupled implicit solver can make the residuals look like they're oscillating when they are in fact decreasing over a longer number of iterations (much depending on your Courant number).

/Henrik

vijay January 31, 2006 11:38

Re: convergence
 
Hi,

The fluctuations are remaining without any deterioration. Even after large number of iterations they are present. I tried again by refininig the grid but it did not work out. Can u suggest anything?

Thanks

kharicha February 1, 2006 04:04

Re: convergence
 
Please refine your boundary layer if you have....not the entire domain. If it doesn't work detail a bit your geometry and phenomena you want to model...


All times are GMT -4. The time now is 09:37.