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Old   March 19, 2012, 16:49
Default divergence transient study
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andres
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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
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Old   March 22, 2012, 14:05
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Quote:
Originally Posted by cfdhydraulic View Post
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.
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Old   March 22, 2012, 14:07
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I will do it, thanks
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Old   March 22, 2012, 17:21
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I set even 10000 in max coarse and it didn't change at all the results...
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Old   March 23, 2012, 13:36
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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.
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Old   March 23, 2012, 13:47
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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!
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Old   March 23, 2012, 14:12
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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!!.
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Old   March 23, 2012, 14:16
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yeah sorry some times I get confused with this forum... sorry about that! no happens again
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Old   March 23, 2012, 14:38
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Try reducing the time step size and simultaneous reduce the URF

Nik
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