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-   -   Grid independence study (http://www.cfd-online.com/Forums/fluent/34290-grid-independence-study.html)

prasanth July 28, 2004 19:59

Grid independence study
 
Dear friends,

To study the grid independency/dependency, how should the mesh size be varied in order to check the solution at different grid sizes and get a range at which there is no variation in the solution.

Thanking you for a kind response!

prasanth

ozgur July 30, 2004 08:43

Re: Grid independence study
 
Hi,

You can adapt your grid and continue you simulation with the refined grid to see whether there is a significant change in the parameters.

regards

wxl July 30, 2004 10:59

Re: Grid independence study
 
Do you mean that we don't have to redo the meshing in gambit, instead, we only need to adapt grid in fluent? Thanks.

prasanth July 30, 2004 15:42

Re: Grid independence study
 
Hello Ozgur

Thanks for your reply. But, I know what you are saying, adapting the grid to refine mesh at locations of high gradients!!

but I am talking about grid independence studies!! you will take 3-4 different grid sizes and like that, repeat the simulation until we get no change in solution!

Thanks prasanth

Chetan Kadakia August 4, 2004 16:57

Re: Grid independence study
 
I believe you can modify the grid based on different methods (not just high gradients), and when you are convinced that adapting the grid anywhere will not change your outcome, then you are grid independent. Your solution is 3D, the continuous adaption may not be practical. You can also refine the grid in Gambit as it seems you are about to do, but do decide where you want to make your changes based on what you are studying in the flow. May I ask what you are simulating, what model you are using, and how many cells you are going to have in your various meshes.

ajb August 9, 2004 19:01

Re: Grid independence study
 
A good rule of thumb I use is 15 to 25% difference between subsequent grids. Sometimes it is necessary to refine grids in order to achieve values of pressure, velocity, turbulent reynolds number, y+ (if turbulent flow), etc that are appropriate. Then once those values are "believable" or close to experiment, refine grid with something like 3 or 4 or more densities. If you are in hexahedrals, you can refine in one direction at a time to ensure there is no effect from grid. Or if in tetrahedrals, a gross refinement of total cell sizes would be O.K. Finally, if tetrahedrals are use, it is always a good idea to try to create hex grid that is very close to the density of the tet grid so you can see whether there is effect of grid type. Hope it helps.


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