Experimental Investigation of the Far-Field Noise Generated from the Cruise Configuration of Aircraft High-Lift Device

Abstract

Air traffic has developed rapidly in the last decades. The noise generated from aircraft can impair the health of passengers and airport residents, so it is necessary to reduce aircraft noise and relieve the annoyance due to aircraft noise. As one important component of aircraft wings, the high-lift device is a barrier to the noise reduction of the large commercial civil aircraft in the next stage, especially during the approach and landing phases. When the slat and flap of the high-lift device are both stowed, some gaps and cavities will emerge and radiate strong noise. However, little attention has been paid to these geometric structures on real aircraft. This paper presents an experimental investigation on the far-field aeroacoustic characteristics of the stowed 30P30N high-lift configuration in the cruise condition, namely with slat and flap both stowed absolutely. The experiment of acoustic field measurements with a far-field microphone and acoustic microphone array shows that the gap between the main element and stowed flap on the pressure surface is the main noise source and can radiate tonal noise in the low-frequency range. The flow field measurement aided by a hot-wire anemometer reveals that the frequencies of the intense fluctuations near this gap are close to the tonal frequencies in the far-field noise spectra. Finally, with the applications of a gap cover and tripping device, the tonal noise of the stowed 30P30N high-lift configuration can be obviously suppressed because the feedback loop between the boundary layer instability upstream and the pressure wave from the flap–main element gap has been disturbed.