free surface bc using pressure correction method

Sal

Hi, Does anyone have experience with specifying a free surface boundary condition for 2d, incompressible flow using a pressure correction method (SIMPLER method using control volumes)? My results are very close to correct, but not quite; there seems to be a slight problem w/ how best to specify the normal velocity gradient at the surface. Should the viscosities in the ghost cells at the upper boundary be those for the fluid, or for air? I'd be very thankful for any help. Thanks -