need help convergence problem

mahmoud ali saad · February 12, 2020, 23:57

hi all , i need help with my model . the problem is with residuals in continuity dosent reach 10-3 and by monitoring the results doesn't reach constant value .
solver setting :
simplec , second order scheme for pressure and quick scheme for all other convection parameters.
the model and mesh and results in photos

vinerm · February 13, 2020, 03:24

Mahmoud, for such a system, prefer using Coupled with pseudo-transient. Furthermore, no need to use QUICK. Difference between QUICK and second-order would be too small.

mahmoud ali saad · February 14, 2020, 04:45

Quote:

Originally Posted by vinerm

Mahmoud, for such a system, prefer using Coupled with pseudo-transient. Furthermore, no need to use QUICK. Difference between QUICK and second-order would be too small.

THANKS vinerm , its works but the coupled solver induced back flow(rise the error) even with down steram flow 2.5times the model length .so what is your recommendations for that problem.
great thanks for your help

vinerm · February 14, 2020, 05:05

In some cases, flow reversal is realistic, such as, for cases with obstructions very close to the outlet. Otherwise, you should observe that as the iterations proceed, the number of faces having flow reversal reduces. In case it is not reducing then the obstruction is too close to the outlet and you should extend the domain; recommended is 6 times the hydraulic diameter away from any obstruction. If reversal exists only on a couple of faces, you can ignore that. Extension would not be justified.

February 13, 2020, 03:24	Use Coupled	#2
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	Mahmoud, for such a system, prefer using Coupled with pseudo-transient. Furthermore, no need to use QUICK. Difference between QUICK and second-order would be too small. mahmoud ali saad likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

February 14, 2020, 05:05	Flow reversal	#4
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	In some cases, flow reversal is realistic, such as, for cases with obstructions very close to the outlet. Otherwise, you should observe that as the iterations proceed, the number of faces having flow reversal reduces. In case it is not reducing then the obstruction is too close to the outlet and you should extend the domain; recommended is 6 times the hydraulic diameter away from any obstruction. If reversal exists only on a couple of faces, you can ignore that. Extension would not be justified. mahmoud ali saad likes this. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

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