Empirical study of the tonal noise radiated by a sharp-edged flat plate at low-to-moderate Reynolds number

Abstract

Airfoils operating at low-to-moderate Reynolds number may produce noise that contains one or more high amplitude tonal components. Many previous researchers have attributed airfoil tonal noise to a feedback loop between instabilities in the laminar boundary layer and the acoustic waves produced at the trailing edge. There is, however, limited experimental evidence to verify this proposed hypothesis. This paper presents results of an empirical study on the tonal noise produced by a sharp-edged flat plate at low-to-moderate Reynolds number (0.7 × 105 ≤ Rec ≤ 2.3 × 105, based on chord). Simultaneous measurements of the far-field noise and flow about the plate's trailing edge have been acquired in an anechoic wind tunnel at the University of Adelaide. An empirical formula is derived to estimate the tonal frequencies produced by flow past the flat plate. A feedback model based on that developed by Tam (1974) is applied to the experimental data to demonstrate that the characteristics of the flat plate tonal noise and flow fields do not support an aeroacoustic feedback mechanism. The vortex shedding model developed by Moreau et al. (2011) is reviewed to show that in this particular case, the tonal noise appears to be governed by vortex shedding processes at the trailing edge.