Well, in the end it's about the flip separating the different densitys properly. What I've found out is that the velocity greed seems to "swallow" single flip particles with a different density. Adding a pop force to these air bubbles doesn't help either. The up force is just to weak in order to be noticed by the grid. And if you turn it up, the whole sim looks strange because of the force getting way too strong.

What's your recommendation?

The best thing I can think of right now is a sop solver with an attribute transfer. In the sop I'd separate the liquid and the air bubbles and then transfer the up force from the bubbles to the surrounding liquid. This way the grid cell what get enough lift to move up the enclosed single air particle.

Anybody with another approach?

Cheers
Tom