[MachZero]

Hello,

I am working trying to model the external aerodynamics of an aircraft with an engine inlet. I am not modeling the engine itself but rather am applying a negative static pressure at the inlet plane to simulate the effect of the engine.

In this case the engine is mounted on the bottom of the aircraft, and a boundary layer diverter is used. For those unfamiliar, this means that the engine is lifted off the surface of the aircraft to minimize effects from the boundary layer that has built up on the aircraft. For arguments sake, the diverter is basically the leading edge of a symmetrical airfoil, acting as a pylon.

In my mind, this problem should be very simple. The aircraft is symmetric so half the flow should go to the left of the diverter, and half to the right. However there is some sort of instability formed under the engine inlet at the diverter. A vortex is created and the instability goes wild, air moves into and out of the engine inlet back and forth, and the simulation does not come to a steady state. I dont believe this to be a real phenomenon, but rather an artifact of the simulation.

The freestream Mach is 0.3, and therefore I am using a coupled solver. I do no use this solver much, so I simply use a CFL = 1.5 and leave it.

I know this is a bit vague, but has anyone seen anything like this and have any idea how to solve this issue? Or if you have any solver methods or suggestions I would love to hear them. Lastly, I am using Star CCM+ as the solver.