A rigid body being moved by water within a dynamic mesh.
 

Dear all, I have a cylinder involving a piston being moved by water, as depicted in Figure 1. The water exerts a force on the piston, pushing the water located behind the piston towards the outlet. The mesh employed has an element size of 0.15 mm. I have compiled a User-Defined Function (UDF) in ANSYS Fluent for the properties of water density, water sound speed, and the motion of the piston as a “rigid body” as in the corresponding TXT File. Most simulation settings are in figures 2 through 9. The time step is 0.001 sec.
In my attempts to solve this problem, I have explored three different solution methods: SIMPLE, PISO, and Coupled. Unfortunately, all three methods have yielded the same result – convergence has not been achieved.
I kindly request assistance from anyone who can identify the errors in my work. Furthermore, I would appreciate guidance on how to correctly implement this simulation.
Thank you in advance for your support.