boundary conditions for compressible flow

George

Hi everybody, I am writing a finite volume code for unsteady 3D turbulent compressible flow in an internal combustion engine.The boundary conditions that I use is prescribed velocity at the inlet and moving wall at the piston head.But I want to make some measurements of swirl,so I must set the piston's velocity to zero.Then it is like fluid entering the cylinder and it is very compressed,like the fluid entering a closed box.The velocity is again prescribed at the inlet.But the code does not converge.The mass residual is only 0.001 but the other residuals are just fine (0.00001).What boundary conditions should I use in order for my code to converge?Can a code converge,when there is one inflow and three walls (no outflow)?My code follows the SIMPLE method for compressible flow. Thank you