simulate a tank equipped with propeller inside

aloha5i

when the propeller is rotating, it makes bulk flow in the tank for mixing. Now I am going to find out the flow pattern in the tank. In my simulation, two domains are made. One is rotating, another is stationary. The boundary conditions as follows: tank bottom: No slip wall tank wall: No slip wall propeller hub and blades: No slip wall(rotating) Water level(water surface): free slip wall

It can be seen, in this simulation there is no inlet and outlet. And it is a steady state simulation.

However, I can not get convergence. the residual is about 1*10^-3 after 500 iterations. Then it goes to be flat.

I have no ideas what's wrong with this calculation. I am wondering that maybe because of the boundary conditions are not right. especially, the waterlevel is considered as a free slip wall. But I am not sure.

Is anybody have experience on this kind of simulation. or please comment is it right to consider a waterlevel as a free slip wall in this task.

thanks