Airframe Noise Studies on Wings with Deployed High Lift Devices

Abstract

Employment of very quiet high-bypass-ratio engines to propel current and future "very large aircraft" has caused airframe noise to become a significant contributor to the overall radiated noise from an aircraft in landing approach. To understand the noise generation from aircraft components deployed during the final approach leg, such as landing gears and high-lift devices (HLD) on wings a German National Research Project was initiated, culminating in a series of model- and full-scale wind tunnel experiments on HLD. Initial results from HLD-studies in the DLR Aeroacoustics Wind Tunnel Braunschweig (AWB) are discussed where an acoustic mirror was employed on a 1/10 scale-model wing section to identify the aeroacoustic source mechanisms of slat-noise and flap side-edge noise. Tests were performed for different flow velocities and wing angles-of attack, indicating that the very slat tracks constitute sources of excessive flow noise. Moreover, both slat-noise and flap side-edge noise, respectively, were found to each be a result of specific combinations of different unsteady-aerodynamics mechanisms. Several, though still perliminars noise reduction techniques were tested.