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-   -   divergence transient study (http://www.cfd-online.com/Forums/fluent/98802-divergence-transient-study.html)

cfdhydraulic March 19, 2012 16:49

divergence transient study
 
Hi folks
I am performing a transient study and after 3000 iterations it takes place a divergence of residuals and so my results...

Is is:
Density-based
Energy On
Laminar Flow
Courant Number 0.1 (which works perfect)
Implicit
Second Order

Transient condicionts:
Time Step Size = 0.1 seg
Number Steps = 5000
Max Iter/ Time Step = 50


Everything runs well and behaves as supposed but when it reaches 3000 iterations....diverges!

Any advice?? is there anything else I can do??
Any suggestion??

Thanks in advance

Regards

banty March 22, 2012 14:05

Quote:

Originally Posted by cfdhydraulic (Post 350291)
Hi folks
I am performing a transient study and after 3000 iterations it takes place a divergence of residuals and so my results...

Is is:
Density-based
Energy On
Laminar Flow
Courant Number 0.1 (which works perfect)
Implicit
Second Order

Transient condicionts:
Time Step Size = 0.1 seg
Number Steps = 5000
Max Iter/ Time Step = 50


Everything runs well and behaves as supposed but when it reaches 3000 iterations....diverges!

Any advice?? is there anything else I can do??
Any suggestion??

Thanks in advance

Regards

Hello,

Plz Increase the maximum coarse level under multigrid panel (Advanced solution control)
and lets see its works or not.

cfdhydraulic March 22, 2012 14:07

I will do it, thanks

cfdhydraulic March 22, 2012 17:21

I set even 10000 in max coarse and it didn't change at all the results...

banty March 23, 2012 13:36

no, even 10 is sufficient. 10000 is not correct(unreal). u can play with multigrid option. (pre sweeps, post sweeps) . hopefully it will help.
http://https://www.sharcnet.ca/Software/Fluent12/html/ug/node794.htm

r u using explicit method to time advancement? ( u set courant no 0.1.)
try using implicit method and please post whether it is working or not.

cfdhydraulic March 23, 2012 13:47

yes I am using implicit method (itīs default) , and it gives me the possibility to set courant number. I have tried from 0.1 to 5 (0.1 more precise but slower and 5 very coarse)

max coarse number didnīt affect my calculations nor residuals.

I am going to surf this site and Iīll let you know!
Thank you!

banty March 23, 2012 14:12

Hello cfdhydraulic,

Plase don't make different thread for same problem as i think u have two or three threads for this problem. its confusing, right!!.

cfdhydraulic March 23, 2012 14:16

yeah sorry some times I get confused with this forum... sorry about that! no happens again
:)

nikhil March 23, 2012 14:38

Try reducing the time step size and simultaneous reduce the URF

Nik


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