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-   -   Instability in buoyantSimpleFoam (http://www.cfd-online.com/Forums/openfoam-solving/58627-instability-buoyantsimplefoam.html)

smehdi609 August 20, 2008 15:26

Dear Foamers, I am simulating
 
Dear Foamers,
I am simulating two co-axial mixing jets, one cold and one hot with buoyantSimpleFoam. The iterations goes on until the residuals reach 3e-5, suddenly it becomes oscillatory and diverges !! If I under-relax density calculation then it works pretty well. I was wondering why?
The central jet has a Reynolds number of 20,000, and the other one has 4000. I use upwind differencing for convective fluxes.
Cheers,
Mahdi

lillberg August 20, 2008 15:38

Dear Mahdi, The reason is l
 
Dear Mahdi,

The reason is likely that you have a larger scale oscillatory behaviour of the jets that has to be heavily relaxed to find a steady state solution. Likely you could relax either entalpy or even pressure and come up with the same solution.

Best Regards

-Eric


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