simpleFoam crashing
 

Hello everyone,
the last few times my simpleFoam simulations always crash and I absolutely don't know why (I'm quite new to OpenFOAM and this may be the reason why I've got such problems :rolleyes:). I've already looked through many threads here but haven't found a solution yet.
Some background information about the simulation: I want to simulate a coaxial system, where I have an inner cylinder (radius 12.778 mm) and an outer cylinder (radius approx. 13.943 mm). The inner cylinder has a smooth surface and rotates, the outer cylinder has a structure (rectangular grooves) and doesn't move. In between these cylinders there is a newtonian fluid with a viscosity of approx. 5 Pa*s (silicon oil). To simplify the simulation, I only look at one eigth of a full circle and also not at the full length of the cylinders, but only 0.5 mm. The aim is to get the torque at the inner cylinder (called innerWall, outerWall is the structured outer cylinder). In the files, sideX is the "open" side at the x-axis, the same applies to sideY. top and bottom seem to be clear ;)

What i recognized so far: at some point in the simulation, first the torque around the y-axis (viscous_y) has a sudden jump (see file "moment" at t = 3666) and then the desired torque around the z-axis decreases for some more time steps (as it should), but then increases. This jump can also be seen in the velocity field in paraview. At t=3000 everything looks fine, but at t=4000 it's quite a mess in one region. The same happens at t=9000. I also checked the mesh, but this seems to be ok, see file "checkMesh" (created with snappyHexMesh).

I hope anyone knows a solution for that. If you need any further information, feel free to ask. The whole mesh was too big, so I only attached the boundary file.

Regards
flashsepp