Dynamic mesh for concentric cylinders
 

I am trying to model the flow of particle/fluid mixture in the annular gap of two concentric cylinders, in which the inner cylinder is spinning. I was told that I need to set up a dynamic mesh, but I am new to Gambit and Fluent and have no idea where to start. I imported the geometry from NX as a IGES file, but I am not sure what to do next.

Please help!!

After importing, build your fluid domain.
Then the question is: do you really need dynamic mesh?
Check help (10. Modeling Flows with Rotating Reference Frames)