Flow Investigations in a Stalling Nacelle Inlet under Disturbed Inflow

A generic, cold flow-through nacelle under atmospheric disturbed inflow was experimentally investigated. The boundary layer development of the nacelle resembles that of a powered engine at take-off conditions and high mass flow rates. A vortex generator was positioned l/c(n) = 3.3 in front of the nacelle's leading edge in order to generate an inhomogeneous inflow. This vortex generator is a motor driven airfoil, which pitches from angles of attack alpha(vg) = - 11 degrees to alpha(vg) = 11 degrees within approximately 58 ms. This way, vortices are generated in the wind tunnel. These vortices induce an upward velocity component which is comparable to a realistic gust. The investigations are performed for attached, as well as separated, flow in the nacelle. It is shown that for the attached flow the low speed near-wall area and the turbulent fluctuation velocities are increased. For the higher angle of attack of the nacelle, the interaction with the generic gust increases the size of the turbulent separation bubble as well as the amplitude of the fluctuation velocities. In both cases the changes might lead to problems on the compressor of a powered jet engine. The results indicate crucial distortions due to the interaction of the relatively small generic gust with the flow through the nacelle.