Convergence issue

dhaya400 · December 3, 2014, 13:40

Hi,

During my flow simulations in fluent, the residuals never meet the convergence condition but also no longer decreasing.

I also run the case by changing under-relaxation factors, but its showing same behavior.

I am using SIMPLE algorithm and second order upwind scheme for discretization.

How can I judge whether it is converged or not?

with regards,
Dhayananth

student2008 · December 5, 2014, 09:58

Hi,

convergence is often a big issue. You should not only look at the residuals. I would recommend you to plot some solution variables, you are interested in. They can tell you whether or not your solution is converged.

To lower your residuals I would recommend you:

- use the first order upwind schemes, they are easier to converge
- try increasing/decreasing the URF. I had some trouble with continuity and increasing the pressure URF helped
- If you are using coupled, reducing the courant number might help

regards
student

December 3, 2014, 13:40	Convergence issue	#1
dhaya400 Member Dhayananth Join Date: Jun 2014 Posts: 37 Rep Power: 11	Hi, During my flow simulations in fluent, the residuals never meet the convergence condition but also no longer decreasing. I also run the case by changing under-relaxation factors, but its showing same behavior. I am using SIMPLE algorithm and second order upwind scheme for discretization. How can I judge whether it is converged or not? with regards, Dhayananth

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December 5, 2014, 09:58		#2
student2008 New Member Join Date: Jun 2013 Posts: 14 Rep Power: 12	Hi, convergence is often a big issue. You should not only look at the residuals. I would recommend you to plot some solution variables, you are interested in. They can tell you whether or not your solution is converged. To lower your residuals I would recommend you: - use the first order upwind schemes, they are easier to converge - try increasing/decreasing the URF. I had some trouble with continuity and increasing the pressure URF helped - If you are using coupled, reducing the courant number might help regards student