shear boundary condition
 

Hello, I'm new to CFX and would appreciate it if someone out there can give me a reply, any reply. I am trying to model wind blowing over a reservoir surface. I am trying to avoid the complications of modelling the air moving above it. So instead, I am thinking of applying a shear boundary condition directly at the free surface . Is this possible, if yes, how do i do this? I have tried using a moving wall boundary with a velocity, but I would prefer applying a direct shear.

Thanks for any help in advance!