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-   -   Multiphase Flow - Convergence Problems (http://www.cfd-online.com/Forums/fluent/92584-multiphase-flow-convergence-problems.html)

bastian26 September 19, 2011 07:26

Multiphase Flow - Convergence Problems
 
Hi everyone,

i try to simulate 2d laminar 2phase flow (water - air) with the mixture model and two eularian phases.

the geometry is a rectangle which is filled 50% with water and 50% with air.
There is an velocity inlet (air) at the bottom so that air passes through the water phase (inlet veloctity=0.005 m/s).

In the phase section, i set the bubble diamater (air - second phase is the air) to 1 mm.
For the interaction:
i choose symmetric for the drag coefficient and manninen et al for slip velocity.

i use the following solution methods:
piso
skewness and neighbor connection = 1
Least squares cell based
body force weighted
quick
quick

time step size is set to 0.001 s with 50 iteration per step

the problem is that immediatly in the first iterations step i get a divergence in the solver (pressure)

i tried also the simple solution methods.

and i tried the standard drag coefficient (schiller-naumann)
then the solution is much more stable but the results arent realistic and after a while - (ca. 3 seconds) it becomes unstable.
I read also in the user and theory guide that you have to use symmetric
if :
The symmetric model is recommended for flows in which the secondary (dispersed) phase in one region of the domain becomes the primary (continuous) phase in another.

like it is in my case.

has anybody ideas what i do wrong?

Thanks!


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