The only two existing phases are water (blue) and air (red), as I had to chose one and regarded it as more physically senseful I set air as the backflow phase and hence it is also the one that is reversing.

I tried lowering the time step by another order of magnitude to 1e-6s, which lies an order of magnitude below the minimum time step when running the simulation with adaptive time stepping at a Global Courant number of 0.9, and after careful post-processing I still don’t see any effect of the wall rotation on the fluid interface.

I have been trying to understand your advise of “rotating the fluid zone & wall at zero relative”; do you mean following a (single) moving reference frame approach? My current understanding of this is that the momentum equations would be solved in terms of a relative velocity U_{rel} which can be transformed back into a U in a stationary reference frame. By having that moving reference frame additional terms appear in the momentum equation in this case being the Centripetal and Coriolis force and a (d\omega) / (dt) * r term.

- The solution obtained with this approach should differ from the solution obtained by moving the wall by no more than numerical inaccuracies though, right?

DrAmine wrote here Should fluid be rotating or wall be rotating (ansys.com) that the two solutions will only lead to similar results if the centripetal and coriolis forces are low. This confuses me, as it seemingly goes against the reasoning recommended by you and my understanding. Adding the new terms to the momentum equation by solving from a relative frame of reference should be at least physically be the same as solving from a stationary frame of reference and implementing the wall rotation through the boundary conditions, right?

I would be very grateful about a quick clarification on whether this throught process is correct and why DrAmine gave this answer to a similar problem. Thank you very much already for your contribution.