Initiation of expansion wave
 

I am trying to simulate a shock tube problem on either CFX or Star-CD, to study the interactions of the expansion wave with various obstacles. I don't, however, know how to approach setting up such a problem on these packages. I do know that ideally I need an outlet where I can set flow conditions (Temperature, pressure, velocities, etc.) and an inlet that will initially have set conditions but must not reflect any waves passing it. I would appreciate any suggestions on how to achieve this.