Creating bubbles with a FLIP fluid simulation requires removing the FLIP particles where you want to create a bubble and then enabling Enforce Air Incompressibility on the FLIP Solver. This feature prevents air pockets from collapsing and can be used to create rising bubble effects.
Make a rising bubble in a tank
Create a FLIP Tank for simulating bubbles.
Add a Sphere in the tank and modify its size and placement to create the desired initial bubble shape.
Create a Sink from the sphere and select the FLIP Tank to add the sink to.
Make sure to adjust the division size of the Fluid Source to account for any changes in the sphere size.
This does not work with Adaptive Pressure solves.
Set the activation of the Source Volume to generate a bubble at the desired frames.
Enable Enforce Air Incompressibility on the Air tab of the FLIP Solver so that the bubble created by the sink doesn’t immediately collapse.
If you encounter bubble volume changes during the simulation, it might be helpful to enable Detect Droplets on the Droplets subtab of the Particle Motion tab, and set the Behavior to Kill at Fluid. Adjusting the Min/Man Particle Density will also help control the volume change.