Localisation of noise sources around flaps
Aircraft noise is an evident environmental problem. Since the number of flight movements increases, the noise exposure around airports is giving rise to community concern. As a result, further improvements are required in reducing aircraft taking off and landing noise at the source. Despite a significant progress in reducing aircraft noise in the past, airframe noise has increased due to the use of modern high-lift devices.
In the initial approach the engines of an airplane are working with reduced power, so that the noise produced by the air flow around the airplane has nearly the same order of magnitude as the noise produced by the engines itself and cannot be neglected. Examples are the landing gear, slats and flaps. The following figure shows the acoustic source distribution of an A319 for a third-octave band and a center frequency of 1000 Hz. The sourcemap, based on measurements taken on the Rhein-Main-Airport by the DLR Institute of Propulsion Technology and evaluated at the ILR, shows that the engine and flap side noise are in the same order of magnitude for a center frequency of 1000 Hz. In this figure the noise level produced by the landing gear cannot be seen because the sound is emitted in another frequency domain.
The physical origin of the flap side edge noise is still a subject of research. A generic wing flap model is used at the ILR to study flap side edge noise. The influence of different configurations on radiated noise and flow field is investigated as well.
- Sound source localisation by the microphone array of the Institute of Aeronautics and Astronautics.
The figure shows a source map of the wing flap model for a one third octave band of 6320 Hz. The wing Tip noise and the flap side edge noise can clearly be seen, where the flap side edge noise is the stronger source.
- Surface flow visualization by oil flow pattern
- Flow field measurements by Particle Image Velocimetry (PIV) at characteristic locations of the flap side edge
The figure shows the measured (PIV) flap side edge vortex of the reference configuration at 46 % chord. The colour scale shows the absolute velocity.