I am trying to do the flow simulation to find the velocity profile in the gap between pressure and cylinder.The boundary conditions to the model are 1. inlet velocity to the piston(0.1m/s) 2. Real stationery wall to the cylinder for no slip condition.3.environmental pressure to the open end of the cylinder and the other side is closed.

Am i doing it in correct way?please help!!

Also how can i calculate the pressure inside the cylinder theoretically?

For the further reference i am including my model in the attachment .