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James May 27, 2004 08:41

Convergence Problems
 
I am run a Eulerian Multiphase with a K-epsilon mixture turbulence model using the default discretization schemes for the Eulerian model and the solution will not converge. The model produces patches of high velocity that appear and move around the model which I can't get rid of, however the phase seem to be what would be expected. So far I have tried reducing the under-relaxation factors, a number of grid adaptations, using a second order scheme for volume fraction and change the outlet conditions from an outflow to a pressure outlet. None of which had any effect so I was wondering if anyone encounter such a problem and what they did about it.

Many Thanks

James

ap May 29, 2004 07:07

Re: Convergence Problems
 
Waht equations do not converge?

What kind of wall treatment are you using? I has similar problems using the enhanced wall treatment.

Check the grid. Is it good enough?

First order discretization scheme is not accurate enough, I'd suggest to use at least a second order scheme for all equations, even if this can increase initial convergence problems. If so, you can start with first order and then switch to second order when the solution has been stabilized.

Try to increase the pressure under relaxation factor to 0.5 or 0.6 and to reduce the momentum under relaxation factor to 0.4.

Hope this helps.

Hi :)

ap


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