Effect of Landing Flap Blowing on Side-Edge-Noise Radiation

Kurzfassung

Noise originating from flow over the airframe of large commercial aircraft has gained importance due to the success in high bypass engine noise reduction. Among other sources of airframe noise the edges of lifting surfaces - landing flaps in particular - constitute potential source areas as a result of strong vortices being formed and shed from such side-edges. Aiming at a basic understanding of the related noise generating mechanisms extensive measurements were performed to determine the vortex steady and unsteady aerodynamic characteristics and their correlation with the ensuing farfield noise signatures. Velocity field measurements were performed to localize the flap side-edge vortex, while acoustic farfield data were determined both by means of an acoustic mirror and employing the microphone-array technique, based on the algorithm of acoustic nearfield holography to in addition calculate the acoustic energy flow in the very acoustic near field (the source area). This data was used to establish the correlation between the local unsteady aerodynamics and the radiated acoustic energy and thus describe the relevant noise source mechanism. As one measure to alter the vortex/flap surface interaction process, the effects on both vortex characteristics and radiated side-edge noise was investigated by injection of air through the side-edge plane. Side-edge blowing tends to destabilize the vortex flow. These experiments were performed on a generic wing-flap configuration in the Aeroacoustic Windtunnel Braunschweig.