Prediction of flap side edge noise

Abstract

This paper presents a model for noise generation by flow separation in the flap side edge regions of aircraft high lift systems. The model is based on the concept that complex flow features such as shear layer instabilities that cause flow separation generate noise by producing unsteady vorticity fluctuations. These vorticity fluctuations are modeled here by unsteady nonlinear motions of discrete vortices, representing shear layers in real flows, and by dynamic vortex shedding from the sharp comers of the flap side edges, modeling vorticity production by flow separation. The model calculates the near field flow fluctuations, including unsteady pressures on the flap surfaces, which are then used to compute the far field radiation. Both unsteady surface pressures and far field predictions are compared with available test data, which shows very good agreement in the dominant trends, such as frequency characteristics and flow Mach number dependence.