[sns]

Hello everyone,
Using Ansys Fluent, I am trying to simulate an Archimedean screw sitting on the free surface (half submerged), to determine the thrust produced for a given set of dimensions. below is the setup and some of the problems faced, any help would be appreciated.

Setup : - Transient + Gravity.
-VOF/multiphase/no surface tension.
- k-omega turbulence model.
- Zones Conditions: Cylindrical enclosure of the screw (mesh motion-Rotating)/ rectangular enclosure medium (Static-2 Phases).
- boundary conditions: pressure inlet/ pressure outlet/ atmosphere(pressure outlet)/ everything else is a static wall.
- Methods: SIMPLE, all first order except the momentum 2nd order.

Problems faced: - negative drag force and coefficient when monitoring.
- Drag force taking too many iterations to settle down as if waves are produce initially ( given the small enclosure and the initial rotational velocity of the screw being 50rpm)
- apparent gap at the interface region between rotating and static enclosures ( when looking at contour planes ).
- high flow time needed to reach a settled flow (20 sec minimum, since my time step size is 0.01 to 0.1 with 20 iteration it takes a lot of calculation time)

Also, given my application would you it be better to solve the problem as steady state?

Thank you !