Help needed in configuration of laval nozzle in the windtunnel
 

Hi
I'm working on a project and I need some help, please. I need to perform and check is the laval nozzle which is designed for 2 Ma really keep that parameters in a supersonic wind tunel.
-And I need to check in a what range of pressure (in the inlet) the nozzle has the velocity of 2 Ma? How can I manage it?
The wind tunell is powered by compressed air in the tanks(650 m3) up to 18 atm. The nozzle size is: 300x300x1500mm. I've made the grid in Gambit. But my question is:
-What else apart from nozzle I need to design?
I' ve design the equalizing chamber at the the begining of the flow, then the nozzle, then the measurement chamber, and the tunnel (pipe lenght 12m). The whole task must be done in 2D.
-What kind of boundary conditions at inlet pressure and outlet pressure must be put? Is 18 atm (pressure) at the inlet and 1 atm at the outlet correct?
I make the task using k-epsilon model of turbulence. (ideal gas) The problem is with the mass flow rate! There is a huge loss of mass at the end of designed part od tunnel.
Please give me some advice. Maybe I need to design all tunnel not only part of it??
Thank you in advance.