I have a perforated tubing e.g. 9 inch inside of 12 inch tubing. My initial conditions are that inside of the 9 inch perforated tube is one fluid. In the annulus outside of the 9 inch perforated tube and inside of the 12 inch tube there is a different fluid, fluid number two. How one can set up initial conditions in such a way that the fluids occupy its respective regions at the start of simulation dispite the fact that the regions are interconnected through the perforations openings?