CFD Online Discussion Forums

CFD Online Discussion Forums (
-   Main CFD Forum (
-   -   mesh size and convergence (

ertan April 3, 2009 13:34

mesh size and convergence
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?


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.

All times are GMT -4. The time now is 14:18.