Dynamic Mesh/Layering

Lonn Grandia

Hello all, Would sure appreciate any input anyone may have to the following. I am trying to model (in 2D) a very simple geometry of a solid piston (essentially a slug) traveling down a cylinder. The 2D model is the cross section of the piston/cylinder arrangement taken along it's axial length. The problem is modeled in Gambit as follows. It is actually split up into three sections which proceed horizantally from left to right as follows. The first third has a pressure inlet as the left hand boundary followed by a rectangular grid for the fluid region following the slug. The right hand boundary for this section is a wall which is actually the left hand (trailing) edge of the moving slug. The middle third is actually a space which represents the body of the piston/slug. The third section has a wall for it's left hand boundary which represents the right hand (leading) edge of the slug then a rectangular mesh for the fluid ahead of the slug, the right hand boundary of this section is a pressure outlet. I have a udf which compiles and will move the slug at a constant speed of 1.5 m/s. I have linked the compiled udf to the leading and trailing edges of the slug and have made sure that in one time step the slug does not move further than a grid space. I also have the ideal cell height for the remeshing (in the fluid) set to a value of .002 m. (The delta x on the grid spacing is .002 m). The split/merge constants are set to .5 and by my math this should work fine for the given constant piston speed. The problem is when trying to preview the mesh, the slug walls simply refuse to move and the max and min cell volumes reported back do not chance (ever, even in the first time step). Does anyone have any suggestions on what I might be missing? Thanks so much!

Lonn Grandia