EXPERIMENTAL STUDY ON THE NOISE SOURCE CHARACTERISTICS OF HALF-SERRATED SLATS BY MICROPHONE ARRAY

A serrated slat with an appropriate sawtooth angle can significantly reduce discrete noise in high lift devices. In previous experiments, evaluations of different serrations' noise reduction capabilities were conducted using a consistent pattern along the spanwise direction as full-serrated slats. However, these comparisons were generally made asynchronously through noise measurements from several microphones. In this study, by dividing the slat region into two symmetrical parts with different configurations, a synchronous measurement of noise sources from different slat’s attachments is conducted by a 64-channel microphone array. By employing source power integration methods in both the frequency and spatial domains for half-serrated slats, the microphone array distinguished noise sources from different regions and produced the corresponding spectra strength. Additionally, using wavelet beamforming methods in the time domain, the intermittency of noise sources at different regions was evaluated simultaneously. The results indicated that noise-increase serrations produced a strong noise at a lower mode in the time domain. In contrasts, noise-decrease serrations succeeded in reducing the total noise, but failed to further increase the intermittency brought by the noise-increase serration in both the time and spatial domains. Although unsteady noise near the junction parts contributed to a frequency deviation in half-serrated slat cases, it is effective to direct compare the influence of different serration with baseline cases by the microphone array.