Residuals problem

May 4, 2004, 04:05

Hello everybody!!! I have a problem with the continuity's residual convergence.I use the k-epsilon realizable model and I have about 17000 cells. The calculation converges very well at the beginning of the calculation but just before the half of the calculation, the continuity's residual gets instable and doesn't converge. For information, the under-relaxation factor for pressure is 0.3 and 0.7 for the momentum.I have 200 time steps of 5e-4 seconds and 1000 iterations per time step. If anybody has an idea, he will be welcome. Thanks!!

May 4, 2004, 04:12

I think you should try to reduce the under releaxation factor as per the manual.

May 4, 2004, 04:18

0.2 for the pressure 0.5 for the momentum,k and epsilon?

May 4, 2004, 07:21

yeah may be

May 4, 2004, 08:06

You should keep your pressure and momentum urf's equal to 1. So if pressure = 0.4 momentum = 0.6.

This was discussed in this forum sometime ago but I can't remember under what heading, sorry.

Eric

May 4, 2004, 08:48

i think the sum should be 1.0 only for the SIMPLEC method as I understand in the FLUENT guide

May 4, 2004, 04:05	Residuals problem	#1
steph Guest Posts: n/a	Hello everybody!!! I have a problem with the continuity's residual convergence.I use the k-epsilon realizable model and I have about 17000 cells. The calculation converges very well at the beginning of the calculation but just before the half of the calculation, the continuity's residual gets instable and doesn't converge. For information, the under-relaxation factor for pressure is 0.3 and 0.7 for the momentum.I have 200 time steps of 5e-4 seconds and 1000 iterations per time step. If anybody has an idea, he will be welcome. Thanks!!

May 4, 2004, 04:12	Re: Residuals problem	#2
bob Guest Posts: n/a	I think you should try to reduce the under releaxation factor as per the manual.

May 4, 2004, 04:18	Re: Residuals problem	#3
steph Guest Posts: n/a	0.2 for the pressure 0.5 for the momentum,k and epsilon?

May 4, 2004, 07:21	Re: Residuals problem	#4
bob Guest Posts: n/a	yeah may be

May 4, 2004, 08:06	Re: Residuals problem	#5
Eric Guest Posts: n/a	You should keep your pressure and momentum urf's equal to 1. So if pressure = 0.4 momentum = 0.6. This was discussed in this forum sometime ago but I can't remember under what heading, sorry. Eric

May 4, 2004, 08:48	Re: Residuals problem	#6
steph Guest Posts: n/a	i think the sum should be 1.0 only for the SIMPLEC method as I understand in the FLUENT guide

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