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mesh size and convergence

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Old   April 3, 2009, 13:34
Default mesh size and convergence
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Ertan Karaismail
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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.
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Old   April 3, 2009, 15:54
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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 ?
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Old   April 3, 2009, 16:15
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Ertan Karaismail
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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.
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