[GJ_hit]

I use Ansys Fluent 14 in a 2d case for a crossflow fan simulations. The rotary domain around the fan is connect with the stationary domain through the interfaces. The interfaces is a pair of circle connectors with the same radium and center so that I can keep there are no gaps between the interfaces. But after run this case about 6000 time-steps(about 40 periods). Gaps can obviously find between the interfaces. The velocity filed is broken near the interfaces. I am sure that the rotation axis is right. The gap is all around the inner interface and it seems that the radium of the rotary domain changed small.
It is really strange. I use the previous motion command to exam the mesh .I find if I use a large time step size and a small number of time steps the question will not appear. It seems that the size of gap is influenced by the number of time-steps . The RPM Is high in this case, a large time steps lead to convergence difficult.
Is there anyone have similar experience ?can give me some suggestions?