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-   -   GAMG vs. PCG in fvSolution (https://www.cfd-online.com/Forums/openfoam-solving/90806-gamg-vs-pcg-fvsolution.html)

grandgo July 21, 2011 04:39

GAMG vs. PCG in fvSolution
 
hi foamers,

i'm working with two domains of exactly same geometry and case configurations. one domain has 150000 cells, the other about 6*10^6 cells.

in the coarse domain case the GAMG solver needs about 30 iterations for one timestep (nCellsInCoarsestLevel = 1000). on the other hand, if i choose PCG the calculation needs 230 iterations.

in the fine domain case it's the opposite: PCG needs about 1000 iterations but GAMG does need more (maxIter limitation at 1500, various nCellsInCoarsestLevel).

what's your experience with GAMG? any tips what i could try?

best regards
grandgo

Antony_Bosco November 13, 2015 09:58

Hi,

Did you find any answer?

I am solving a external flow simulation. When i increase the number of layers and decrease the min thickness close to 9.6e-06,in a GAMG solver the iterations reach close to 1000 and crashes but on the other hand PCG works very well.

Is there any reason behind.

Thanks,
Antony

KateEisenhower March 7, 2017 08:38

Hi,

Thanks for opening this topic. I have two suggestions:

1) Some people here on the forum say nCellsInCoarsestLevel shouldn't be above 50. On my cases I always make sure to make a "nCellsInCoarsestLevel-study".

2) I think your post would be even more meaningful if you would tell us the calculation time/iteration or per timestep. The number of iterations alone is not so meaningful from my point of view.

Best regards,

Kate


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