Hi, Im doing a unsteady simulation of a pump. Im using sliding and deforming mesh functions. After som timesteps (seemingly random) the mesh will degenerate to a mesh with a small amount of left handed cells. Does anyone know what could cause this?

when you are using sliding mesh , since evry time step the mesh is adjusted..some times if the things are not spcified correctly the mesh may enter into another giving these sort of errors. please check the mesh motion parameters, specially the axis of rotation (origin and direction vector, but some times mistakenly specified as point1 to point2 axis),

well, I looked att the parameters controlling the motions, and it should be impossible that the meshes collide. Also the error appears randomly, suggesting that the problem lies somewhere else. For now I solved the problem by using a funcion "repair face handedness" every time it occurs, which of course is annoying. Why Fluent doesnt do this automatically when generating the new timestep mesh is beyond me. Does this function have such major drawbacks that it is unadvicable to use?

in grid menu there is a option for reordering .. have you tried that .. might be help ...