Backward-facing step simulation

Keith

I am trying to repeat the results in a paper by Gartling D.K(1990). The problem is a backward facing step problem. During the simulation, it seems that the velocity blows up after a certain time. I was wondering if the time step I have used is correct. My spatial step is 0.05m(for all three directions, x, y and z) and my time step is 0.0025 sec. the maximum velocity at the inlet is 1.5 m/s while the average velocity at the inlet is 1 m/s.

Another question I have is regarding the adjustment of pressure field,after a solution is obtain, such that the pressure at the step is zero. Do I have to solve the pressure poisson equation again or do I just set the pressure at the step corner to be zero?

Can anyone advice me on these issues? I really appreciate any help available.