Defining a velocity in a moving plane
 

Hi everybody!

Here is my problem: I'm simulating a single bubble rising. I'm getting ok results, but because of the very refined mesh, the domine extension, and the low time-steps, is taking too long to calculate, even using adaptative mesh refinement.

So I want to use a periodic boundary condition to mimic the very long column. The problem is: when the bubble reach the top and transport to the bottom it is influenced by it's perturbance in the water, so i want to create a plane that is always a certain distance from the bubble top and is a boundary condition, so that in this plane the velocity are 0.

It's like a eraser that moves in front of the bubble and "delets" it's history in the domain, is it even possible to do in fluent with a UDF? If it is, somebody could help me?