A modeling problem of flow in a tube
 

Hi, I am getting started with CFX5.7 using CAD2Mesh.

The constant area tube is open on one side, closed on the other. A small part(1/10) of the tube near the closed side is filled with this high pressure air, which travels to the open side at time 0. (it's like a very thin plate holding the high pressure air and then been removed very quickly) In CFX5.7, how do I model this high pressure region?

Thanks!