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-   -   Coarsening Rate for Radiation (http://www.cfd-online.com/Forums/cfx/22175-coarsening-rate-radiation.html)

Forrest February 13, 2006 08:00

Coarsening Rate for Radiation
 
Hi all,

I am wondering something about the coarsening rate in cfx5.7.1 solver. The intension of it is to reduce the radiation elements in order to same computing time. The problem is that when I model a thin participating solid and the cell numbers on the thickness direction are only about 25 or 35 (hex), if this direction is divided by the default coarsening rate (64) I should have less than 1 radiation element along the thickness, this is confusing because the solver doesn't show any message about this and continue the simulation. While if this is the way the coarsening algorithm does, I want about 15 radiation elements along the thickness, so my coarsening rate has to be 2, or even without coarsening. This makes the simulation time much longer than a normal calculation. Am I wrong to estimate it by this way?

Thanks a lot

Regards, Forrest


opaque February 13, 2006 10:32

Re: Coarsening Rate for Radiation
 
Dear Forrest,

The coarsening algorithm is not deterministic..You control the target (which may not be achieved under multiple scenarios) coarsening rate, and the CFX solver tries to give you that..

It does not have fine controls on how it coarsens boundary elements, interior elements, or direction of the coarsening.

The coarsening does not cross domain boundaries. If you have a mesh with 10 elements, and you set a coarsening target coarsening rate of a million you get 1 element, same if you set it to 64 (default).. It cannot of course coarsen below 1 element..

Good luck, Opaque..

Forrest February 13, 2006 10:42

Re: Coarsening Rate for Radiation
 
Opaque, thanks a lot for your answering, you are helpful always.

So if I have 20 cells across one direction of a domain and I used a target coarsening rate 10 (say the actual coarsening rate is the same), it doesn't mean that I have 2 radiation elements along that direction because the algorithm is not deterministic. But how do I judge I have enough radiation elements to resolve radiation along that direction?

Regards, Forrest


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