Guidance needed regarding the convergence

sidharth9426 · October 6, 2015, 11:47

Dear Experts,
I am right now doing a project of Under hood thermal management, in which I am modelling flow of air using Star CCM.

This like first simulation of CFD, I am doing with star ccm, so I needed advise on the convergence, that how is the entire process of the simulation to be approached so that convergence is achieved.

I read on different portals that I need to start with default value of URF and then wait for convergence, if it is not happening then I need to switch to lower values of URF. And also I need to play with different mesh sizes if convergence is not happening.

So I want to know that, What is like standard procedure followed to achieve convergence? I know it may involve variations of mesh and URF, but how this problem is approached by CFD engineers, industrially??

Regards,
Sidharth

wadeellis · October 6, 2015, 13:36

The mesh size definitely has an effect on the convergence, as well as an effect on the time it takes to reach it. You may want to start out with a broader mesh (but not too broad) so that iterations can happen faster to see if it is converging at all, then narrow the mesh to help it to converge to better values. The values for the mesh size will depend on the size of what you are doing.

sidharth9426 · October 7, 2015, 00:03

Dear wadeellis,
Thank you for the guidance.. I will try what you said... And is the similar process followed industrially, as this process seems to take time to come with perfect results, so how do CFD engineers go around this problem of convergence in industry..? I mean what is their approach..??

.

Regards,
Sidharth.

Bharatt · October 7, 2015, 05:49

Hi Sid,

Here is a very good description on this topic.

http://www.cfd-online.com/Forums/flu...nvergence.html

Hope this will help

Cheers,
Bharat

sidharth9426 · October 7, 2015, 06:26

Dear Bharat,
Thank you for the link..
So I assume that the process of convergence is a trail and error process, right??

..

Regards,
Sidharth

wadeellis · October 7, 2015, 10:55

Unfortunately, I don't have any industrial experience with this program. I use it in my research. But yes, there is a significant degree of trial and error when trying to reach convergence.

October 6, 2015, 11:47	Guidance needed regarding the convergence	#1
sidharth9426 New Member Sidharth Join Date: Sep 2015 Posts: 29 Rep Power: 11	Dear Experts, I am right now doing a project of Under hood thermal management, in which I am modelling flow of air using Star CCM. This like first simulation of CFD, I am doing with star ccm, so I needed advise on the convergence, that how is the entire process of the simulation to be approached so that convergence is achieved. I read on different portals that I need to start with default value of URF and then wait for convergence, if it is not happening then I need to switch to lower values of URF. And also I need to play with different mesh sizes if convergence is not happening. So I want to know that, What is like standard procedure followed to achieve convergence? I know it may involve variations of mesh and URF, but how this problem is approached by CFD engineers, industrially?? Regards, Sidharth

October 7, 2015, 05:49	Convergence	#4
Bharatt Member Bharat Join Date: Jul 2011 Location: Delhi, India Posts: 49 Rep Power: 15	Hi Sid, Here is a very good description on this topic. http://www.cfd-online.com/Forums/flu...nvergence.html Hope this will help Cheers, Bharat sidharth9426 likes this. __________________ chapter 3: -crossing the threshold-

October 7, 2015, 10:55		#6
wadeellis New Member Wade Join Date: Jul 2015 Posts: 24 Rep Power: 11	Unfortunately, I don't have any industrial experience with this program. I use it in my research. But yes, there is a significant degree of trial and error when trying to reach convergence. sidharth9426 likes this.

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October 6, 2015, 13:36		#2
wadeellis New Member Wade Join Date: Jul 2015 Posts: 24 Rep Power: 11	The mesh size definitely has an effect on the convergence, as well as an effect on the time it takes to reach it. You may want to start out with a broader mesh (but not too broad) so that iterations can happen faster to see if it is converging at all, then narrow the mesh to help it to converge to better values. The values for the mesh size will depend on the size of what you are doing.

October 7, 2015, 00:03		#3
sidharth9426 New Member Sidharth Join Date: Sep 2015 Posts: 29 Rep Power: 11	Dear wadeellis, Thank you for the guidance.. I will try what you said... And is the similar process followed industrially, as this process seems to take time to come with perfect results, so how do CFD engineers go around this problem of convergence in industry..? I mean what is their approach..?? . Regards, Sidharth.

October 7, 2015, 06:26		#5
sidharth9426 New Member Sidharth Join Date: Sep 2015 Posts: 29 Rep Power: 11	Dear Bharat, Thank you for the link.. So I assume that the process of convergence is a trail and error process, right?? .. Regards, Sidharth