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-   -   Converge problem for multiphase flow (http://www.cfd-online.com/Forums/fluent/37822-converge-problem-multiphase-flow.html)

Jen September 7, 2005 10:59

Converge problem for multiphase flow
 
I am using Eulerian model to simulate two-phase turbulent jet flow in either 2D axisymmetric or 3D region. The primary phase is air, the secondary phase is water. The speed of air is 70 m/s coming from an annular region whose hydraulic diameter is 0.00254 m, and the speed of water is 1.97 m/s coming out from the center whose diameter is 0.000508 m. I use k-e turbulent model. However, I can not get converge result, because the volume fraction equation is difficult to converge.

I tried different ways to mesh the domain (Quad, Tri, Quad/Tri), and tried different methods to make it converge (multigrid, decrease under-relaxation factors, use the result of mixture model as a starting point for eulerian model).

The mass fraction of water is 0.005%, and the volume fraction of water is 6.15E-8. I wonder the reason is the volume fraction of water is too small, so I can not choose either mixture or eulerian model. I remember in the help document, it says when secondary phase volume fraction is less than 10%, use Discrete phase model.

I don't know whether my thinking is right, or there is something wrong with my settings.

Any help will be appreciated.

Thanks a lot!

Jen

Fuping Qian September 7, 2005 19:56

Re: Converge problem for multiphase flow
 
It is difficult to converge the multiphase model. I wonder what is your converging criterion.I think the reason is not that the volume fraction of water is too small. In Fluent help manual, we can see that, for intermediate loading (e.g.0.005%),the discrete phase, mixture, and Eulerian models are all applicable. Hope this can help you.

Jen September 8, 2005 08:47

Re: Converge problem for multiphase flow
 
I use the default converging criterion 0.001. Is that OK? Thax


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