I am trying to simulate steering in an open top beaker. I am having trouble defining my water surface at the top. Right now I have placed a lid and applied open to atmosphere boundary condition but the solver gives an error warning saying "a vortex crosses the pressure boundary".
I am using a rotation region around my impeller and I have defined the bottom lid and the inner surface of beaker as stationary real wall. Please advise how to correctly define the boundary condition at the top.