Open Fan Geometry Boundary Conditions External Aerodynamics
 

I hope I've posted this thread in the correct place, apologies if not. I am currently using star-ccm+ to simulate a fixed wing UAV with tilting ducted fans at its wingtips. (Please see image to see geometry and mesh)

I'm trying to run a preliminary sim to obtain a drag value for my aircraft at cruise conditions to then identify my thrust requirement, but unsure what to set as my boundary conditions for the inlet and outlet faces of my fan. I essentially want an open duct. I have to keep these boundaries as my geometry fails to subtract as it will not be closed and manifold.

I have each face set as a freestream boundary with values in line with my farfield freestream boundary. Does this sound correct to simulate an open duct? My solution looks a bit unstable and I'm pretty confident in my mesh.

free-stream should not be used on the fan so I would be using maybe a mass flow inlet on both ends of the fan since it can be both as an inlet and an outlet and you then know that mass will be conserved if you set the same value

Calculated a mass flow rate and set both faces to this which has helped my solutions converge and simulate better what I need, thanks for the help!