Strange results using fixedValue BC for outlet

Hi all,

I am trying to model a simple Jet Fan, a cylindrical shell with an inlet and outlet using simpleFoam.

Both the inlet and outlet are set to a fixedValue of 16 m/s.
In the beginning the Outlet sucks in air at 16 m/s as expected but after about 150 timesteps the Outlet behaves strangely by throwing stream of air into the domain.

The patch velocity however is maintained at 16 m/s so I presume there is no infiltration of air back into the domain. The behaviour just besides the outlet is quite strange

I tried using other BC for the Outlet like flowRateOutletVelocity, uniformInletOutlet but the same behaviour persists. I don’t know if it has to do with the default tolerances in the fvSolutions or fvSchemes or under relaxation factors.

Has anyone modelled simple fans like these before or experienced a similar issue?

Any input is much appreciated.
Thank you!!

case folder (14.8 KB)