Airframe noise studies on wings with deployed high-lift devices

Abstract

Employment of quiet high-bypass-ratio engines to propel current and future very large has caused airframe noise to become a significant contributor to the overall radiated noise from an aircraft in landing approach. This has brought about a worldwide resurgence of airframe noise studies, to try and understand the aeroacoustics of, and to ultimately control the aerodynamically caused noise from aircraft components deployed during the final approach leg, such as landing gears and high-lift devices (HLD) on wings. In view of European aviation industry to design and build a large commercial aeroplane, a substantial and dedicated German National Research Project was initiated, culminating in a series of model- und full-scale wind tunnel experiments on HLD. This paper discusses initial results from HLD-studies in the DLR Aeroacoustics Wind Tunnel Brauschweig (AWB) 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 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 preliminary noise reduction techniques were tested, showing nevertheless significant promise to enable containment of otherwise excessive slat-noise and flap side-edge noise, such techniques being quite feasible for future full-scale application.