Initializing velocity in a free-surface flow

Hi. I am recently using the vof method implemented in Palabos. I need to initialize the velocity field to a constant on the whole liquid domain. I found the class ConstantIniVelocityTwoPhase3D, which has a Function f in its argument. Is there any example that shows the use of such a function? I don’t quite understand the use of it if the velocity field is constant throughout the domain.

Thank you in advance!

Hi, I also want to know how to use the class ConstantIniVelocityTwoPhase3D. If you got the answer, would it be possible to tell me?