SOR Fails Near Walls
 

I simluate unsteady free-surface flow on a stagger grid (MAC).

I found the SOR (successive over-relaxation) code fails often in the cells next to obstacle cells (wall). This happens when I simulate a high speed flow hitting on the wall. The divergence of the cell is very large, because a lot of fluid rush into this cells at the same timestep, and there are be two or more onstacle faces (whihc fluid can now flow through) in this cell.

How can I solve this problem?