mesh size and convergence

ertan · April 3, 2009, 13:34

Hi all,
I am running an unsteady simulation (in FLUENT) of airflow for a HVAC project. The flow is turbulent and I am using SST k-w turbulence model. Time and spatial discretizations are all 2nd order. Solver is implicit. Time step is 0.001s. The grid I am using can be considered as coarse.

The problem is that the solution (especially continuity) is converging so slowly even though I played aroung the URF of momentum and pressure. I am wondering if grid is the only problem here. Do you have any ideas to share?

Thanks.
Ertan

harishg · April 3, 2009, 15:54

Do you employ the SIMPLE algorithm ? You might need to change your under relaxation factors in that case. Do you employ multigrid for your pressure solver ?

ertan · April 3, 2009, 16:15

I have tried both SIMPLEC and PISO. Fluent uses multigrid scheme for pressure (at least for the current settings). Is it worth to switch to SIMPLE? Decreasing the URF didn't help much. Still it takes about 150 iteration per time step.

April 3, 2009, 13:34	mesh size and convergence	#1
ertan New Member Ertan Karaismail Join Date: Apr 2009 Posts: 17 Rep Power: 17	Hi all, I am running an unsteady simulation (in FLUENT) of airflow for a HVAC project. The flow is turbulent and I am using SST k-w turbulence model. Time and spatial discretizations are all 2nd order. Solver is implicit. Time step is 0.001s. The grid I am using can be considered as coarse. The problem is that the solution (especially continuity) is converging so slowly even though I played aroung the URF of momentum and pressure. I am wondering if grid is the only problem here. Do you have any ideas to share? Thanks. Ertan

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April 3, 2009, 15:54		#2
harishg Senior Member N/A Join Date: Mar 2009 Posts: 189 Rep Power: 17	Do you employ the SIMPLE algorithm ? You might need to change your under relaxation factors in that case. Do you employ multigrid for your pressure solver ?

April 3, 2009, 16:15		#3
ertan New Member Ertan Karaismail Join Date: Apr 2009 Posts: 17 Rep Power: 17	I have tried both SIMPLEC and PISO. Fluent uses multigrid scheme for pressure (at least for the current settings). Is it worth to switch to SIMPLE? Decreasing the URF didn't help much. Still it takes about 150 iteration per time step.