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-   -   convergence at eulerian model (http://www.cfd-online.com/Forums/fluent/104873-convergence-eulerian-model.html)

rayo July 17, 2012 12:21

convergence at eulerian model
 
hi, i have a problem with the residual continuity because that my problem converge to 8x10^-2 and i need that this value converge to 1x10^-3, minimun, please need help, thanks.
http://img833.imageshack.us/img833/3963/forodl.jpg

Marion July 18, 2012 04:33

Hi,

I've had this before, when the mesh is not good enough, for example at the walls when the mesh definition is not consistent with the wall treatment chosen.

When using multiphase flows (cavitation), I also get this when the initialisation is not good. It is usually better to run single phase, get to convergence, and then switch to multiphase. But I don't know if that would apply to your case.

Marion.

rayo July 18, 2012 12:15

Quote:

Originally Posted by Marion (Post 372069)
Hi,

I've had this before, when the mesh is not good enough, for example at the walls when the mesh definition is not consistent with the wall treatment chosen.

When using multiphase flows (cavitation), I also get this when the initialisation is not good. It is usually better to run single phase, get to convergence, and then switch to multiphase. But I don't know if that would apply to your case.

Marion.

hi, thanks for the help, i will try with that.

fafou09 July 18, 2012 13:30

Hi,
I also heard that you could change the under-relaxation factors, and try to lower them. Ex 0.2 for pressure and 0.5 for momentum.
But I am not an expert in fluent. (It might be explained in the Fluent help)
Good luck

Marion July 19, 2012 04:21

You're right fafou09 - and in my cases (with cavitation) Fluent support advised me to go down to 0.05 for volume fraction.
However, I prefer to see if I can get better convergence without changing the urfs too much. it's kind of a last resort solution for me... And sometimes it doesnt work either!

Rayo - are you running 2nd order? You can also try and run 1st order, get to convergence and then switch to 2nd order.

Marion.


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