How to use the function "set Velocity Condition On Block Boundaries"

Hi everyone ;
I want to apply the free-slip boundary for my domain, so I used the command
boundaryCondition.setVelocityConditionOnBlockBoundaries (
lattice, wall1, boundary::freeslip );
I do not know the velocity at my wall so I did not use the command setBoundaryVelocity after that. However, I looked at the examples, they all got the command setBoundaryVelocity after the setVelocityConditionOnBlockBoundaries.
So I am wondering is it compulsory that I have to use setBoundaryVelocity if I want to apply the freeslip ?
Thank you


What do you mean? Free slip is a velocity boundary condition, which copies the tangetial velocity component from a neighbor in the normal direction from the wall. Setting a boundary velocity is needed for the first step of the simulation. Then this value is changing with time.