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-   -   Question about Multigrid in CFX (http://www.cfd-online.com/Forums/cfx/107045-question-about-multigrid-cfx.html)

Anna Tian September 16, 2012 07:13

Question about Multigrid in CFX
 
Hi,

May I ask if there's an automatic way to implement the multigrid method in CFX?

ghorrocks September 16, 2012 07:39

Um, yes - it is the default solver option. So if you have done a CFX simulation you have used a multigrid method.

Anna Tian September 16, 2012 13:25

Quote:

Originally Posted by ghorrocks (Post 381998)
Um, yes - it is the default solver option. So if you have done a CFX simulation you have used a multigrid method.

Thanks. But it seems not work very well. Because from my experience, if we do the multigrid manually, (Run the simulation for the coarse mesh firstly, then come to fine mesh with the result of coarse mesh simulation as the initial value file.), it converges much faster.

Does default multigrid method also work for multi-domain case in CFX?

ghorrocks September 16, 2012 18:48

It is unlikely that any problem you are having with convergence is due to the linear solver, and even more unlikely that the manual control you describe will be any better.

If you are having convergence difficulties it is almost certainly due to some setup issue with your simulation. You should fix that problem rather than trying to tweak the linear solver.

The multigrid solver is the linear solver used by CFX for all simulations. So yes, it can handle multi-domain cases as well.

cdegroot September 16, 2012 19:45

To clarify, the linear solver in CFX uses algebraic multigrid which works on the coefficient matrix directly rather than a hierarchy of grids. As Glenn said it is the default solver and should work quite well in practically all cases. Manually transferring between grids is unlikely to be helpful.


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