[rikfr986]

Hi, I want to modell a piston that is pushed out of a cylinder, see attached picture, using design modeller and ansys meshing for CFX. My problem is how to model the walls around the piston since there will be a "wall-wall interface" that will turn into a wall-fluid interface. How can I tell the solver that there is a wall at the dotted red lines even if it is outside of my fluid domain at first?

Do I have to model the piston as a solid and mesh it as well? Have looked at the immersed solid option but what I can read it doesn't work for multiphase which I will use later. I have a moving mesh more or less working exept for this wall problem.

Hope it was understandable and that someone can guide me in right direction!