The principal reason for employing a moving reference frame is to render a problem that is unsteady in the stationary (inertial) frame steady with respect to the moving frame. For a steadily moving frame (for example, the rotational speed is constant), it is possible to transform the equations of fluid motion to the moving frame such that steady-state solutions are possible. It should also be noted that you can run an unsteady simulation in a moving reference frame with constant rotational speed. This would be necessary if you wanted to simulate, for example, vortex shedding from a rotating fan blade. The unsteadiness in this case is due to a natural fluid instability (vortex generation) rather than induced from interaction with a stationary component.

It is also possible in Ansys Fluent to have frame motion with unsteady translational and rotational speeds. Again, the appropriate acceleration terms are added to the equations of fluid motion. Such problems are inherently unsteady with respect to the moving frame due to the unsteady frame motion