[Belgio]

I want to model a shock tube in Ansys 12, using the workbench (Design Modeller and Meshing). I am making a geometry - a cylinder with r=10cm and length=60cm as a Thin/Surface with 1cm walls. How can I make a separation of two domains? (I mean low-pressure and high-pressure volumes) and where can I do it? (I mean while drawing geometry or while making mesh? or in Fluent directly?)
Thanks in advance
If somebody has file of shock wave project that would be also fantastic if you could send it to me.