Hi, In my problam, There is a cylinder and a psiton that creates gaps in both sides, More precisely, There are three walls - that look like this : |_| and a rigid wall(piston) that moves in sin way up and down ,The piston is narrow in a way that two gaps are created in the left and right sides.

I am only intersting in the flow inside the cylinder, The area over the piston is not intersting. I will totaly appriciate detailed explantion for the soultion of this problam. I realy dont have a clue, I read a little about dynamic mesh and i preffer not to deal with UDF(its sounds complicated)

Thanks a lot in advance, Sha.

Look the tutorial for a sliding mesh

hi, i have the same problam, anyone can advice a simple way to solve this problam ?

My model consists of a box where in the top of it and in the bottom bordering with a moving wall. between the box and the moving wall exist air. the moving wall moves in the x-axis with 10 m/sec. how can give the boundary conditions to the moving wall?

please help me!!!

As I know you need to specify a velocity in the wall you want. You can do this by changing a couple of things in the momentum panel of the wall:

Wall motion: Moving wall

Motion: Relative to adjacent wall (if adjacent cell is air for exemple)

Shear Stress: here there are two options no slip or specify shear. I usually specify shear stress with 0 constant stress on both directions (X an Y) to achieve a velocity profile where the velocity is 0 near the wall.

If you have defined the shape as a solid you have to impose a moving reference frame on bc panel.

I don't know If I have explained it clearly, any doubt ask me for more info. Hope it helps.