VOF simulation problem
 

Hi,

I have a problem in my VOF simulations in FLUENT. I am trying to simulate a stirred tank with a free surface of water in contact with air. The tank is baffled and I am tracking the interface with VOF.
The problem is that in my simulations results after some rotations of the impeller gas enters far away from the surface in the liquid which is very strange. There is almost 10% gas in the liquid! I cannot explain why it is happening like this.
Has anyone had the same problem in VOF simulations? If yes could you please explain me what is the reason and how can I avoid it? Or is it really affecting my surface results?

Thanks,
Parisa