New insights on slat noise based on a revisit of previous experimental-numerical studies

Abstract

The leading-edge slat has been identified as a relevant noise source since the 1970’s. However, many issues regarding the noise generation mechanisms and the appropriate tools to study them are still under debate. Particularly, details of the narrow-band peak generation mechanism and the use of rigid-wall wind tunnels are open issues. The purpose of this paper is to revisit earlier results in the light of recent advances achieved in this topic, in an attempt to better understand these aspects of the slat noise. It is shown that a feedback model that assumes the trailing edge as the main emission spot and a one-quarter-period phase difference between the hydrodynamic and the acoustic fluctuations in this position is corroborated by measurements from different research groups. Based on this feedback model, the uneven relevance of the slat gap, overlap and deflection angle to the peak amplitude can be explained. Mach scaling laws for the narrow-band peak amplitudes substantially higher than the expected fifth power is pointed out in several previously published data, which suggests the feedback nature of the underlying mechanism. Finally, the implications of this mechanism to the set-up of wind-tunnel tests are discussed.