[Fred_Erik]

Hello!

I'm doing a transient rigid body simulation of a rotating cylinder in a bearing sleeve with CFX. Fluid is air as ideal gas, energy equation is isothermal. I simulate only half of the bearing in axial direction with a symmetry plane. For the fluid entry I use an opening with constant static pressure. To realize damping effects I placed the opening some axial distance away from the edge of the bearing. I take a hexaeder mesh designed in ICEM. At the beginning of the simulation the position of the cylinder is concentric to the bearing sleeve. The gap between the cylinder and the bearing sleeve is small (< 0,06 mm). As the cylinder moves due to an acting force the gap is getting smaller and smaller. The overall mesh movement works fine. But when the gap size reaches round about 0,005 mm the first nodes on site of the bearing sleeve move radial over the boundary and I get negative cells. As I use constant mesh stiffness I expected that the radial distance between the nodes would further decrease, but there seems to be a limit. I tried to fix it with different mesh stiffness, but it was not successfull. Maybe a decrease in number of nodes in radial direction in the gap may help, but then I also decrease the space discretization.

I looked for similar threads in this forum, but I found no adequate solution. Does anybody know to handle this problem?

Thanks,

Fred_Erik