Slow convergence

Jesper

Hi CFX 5.7 users. I need some advice regarding slow convergence.

I am using the 2-fluid model, for 3D modelling of a bubble plume with air bubbles in water. I am getting rather slow convergence for a steady-state solution. The residual plots flatten out after approximately 200 iterations. This continues until at least 1000 iterations (I think modelling further is pointless)! There's only small spikes on the residual plot. Only the RMS-residuals for U-MOM(Air) and V-MOM(Air) falls below 1E-04. The rest of the residuals are above this convergence criterium. Especially the RMS residuals for the volume fractions are high (approx. 1E-2). I have used timesteps of both 0.1 and 1 sec.

The results of the simulation look as expected, with a well developed bubble plume. I just think that I should be able to get better convergence, in order to say that I have a well converged solution...

Does anyone have any solutions/has anyone experienced the same problem for 2 phase modelling?

Regards Jesper