nobody has an idea ?
You can't simulate moving part in Flow
You can only simulate moving face (add speed to face), you can't move body.
You can create "dynamic" analyze but without moving bodies, only flow and thermal parameters can change in time.
You can create multiple analyzes for each step of piston move. But there will be no connection betwen calculations. You will need to calculate increase in pressure on your own, and put this value in to initial values. Then you can calculate flow behavior for short period of time and prepare new step.
He's right : no moving mesh in Flow SImulation. For that you will need an other cfd code.
You can only revolve a part around an axis (rotation option) and move a wall (translation and rotation).
Fyi you can also import results from a previous simulation and use them as a "restart" for a new simulation.
Thank you very much for your answers guys. I will try to find another way to deal with that then.