Reply To: Different boundary condition gives weird result

[Rob]

It's a transient calculation so you need to resolve the flow with time, and converge all time steps. The iteration count is irrelevent, it's the number of time steps you need to consider. As you're not resolving the time scales in the domain I'd be very wary of the results. 

Changing the boundary condition means the flow sees a sudden jump in value, again, you need to consider time scale.