How to specify curved piston motion
 

I want to do cold flow cfd analysis of a curved cylinder engine. The piston oscillates in the curved cylinder. In ICE (Fluent) module, we specify cylinder linear faces, but it is for linear piston motion. How can I specify the cylinder curved face or curved path for the piston to follow with each crank angle? Kindly have a look at the attached image of the curved cylinder engine.

Curved Piston
 

You can do this, however, the system is physically useless if the piston is rigid. How do you expect a rigid face, the crown of the piston, to cover two multiple distances? The distance to be traveled by the sides close to higher curvature is much less than those close to lower curvature. So, the piston will move, but the stroke cannot be long enough to be useful.

Its alright, the motion is same as that of a toroidal engine. If one side has small displacement, the other side has a big one. So thats not an issue. Have a look at the image below:
https://lh3.googleusercontent.com/pr...yeSWcvAX8t1Mbw

But I dont know how to apply this condition in Fluent for piston motion. Please let me know about it. Thanks in advance!

Motion
 

This does make sense.

As far as motion is concerned, you just need to give angular motion and not linear one. If you use Dynamic Mesh, then piston will be a rigid body with C.G. at the center of rotation and motion will be angular one without any linear motion.

Define Dynamic Mesh for Piston
 

Kind regards.