Airframe Noise – High Lift Device Noise

Abstract

Abstract High lift devices, together with landing gears, are the main sources of airframe noise during the approach‐and‐landing phase of aircraft flight. Typical high lift devices include leading edge slats and trailing edge flaps. Other high‐lift‐related noise‐generating devices include spoilers if deployed during a steep approach operation. All the above aerodynamic devices are retracted during the cruise phase of aircraft operation. A slat, when deployed, forms a cove region between the slat and the central main element of the aircraft wing. Flow separation, flow recirculation, an unsteady shear layer, and slat settings together generate noise of mainly broadband content. For a flap, the outboard flap side edge and vortex system associated with it are the main sources of noise. The intensity of high lift device noise generally follows a power law of flow velocity. The main sources of noise are identified and described in this chapter. Introduction is provided concerning main semi‐empirical and computational fluid dynamics methods. Noise attenuation methods are also described.