I am new to Flow Sim, I specifically need to model a type of cylinder compression, thus needing a moving mesh....which I know Flow Sim won't do.  The question is, are there any clever ways to work around FlowSim's limitations, and still do a meaningful study.

My idea is to model the system in the expanded state (piston in a cylinder)...and apply a fluid flow at the face of the piston...I would need to make custom fluid properties with VERY high viscosity and the density of steel, so that it acts as a moving piston...when I specify the desired velocity.  The question is, can FlowSim allow that fluid to interact with the rest of the fluid in the cylinder (air)....or is does there need to be some kind of separation membrane?

Any thoughts?  Thanks