The Aeroacoustics of High-Lift Slat Under the Effect of Pressure Fluctuations

Abstract

Low-speed wind tunnel measurements and numerical simulations of unsteady surface pressures on a wing-slat configuration are presented. The unsteady pressures are incorporated into the acoustic formulation of Lighthill & Curle to calculate the level of noise radiated into the far-field. Three main noise characteristics of the slat are identified as: 1) vortex shedding from the slat's trailing edge (high-frequency tonal noise); 2) unsteady fluctuations caused by turbulence interactions over the slat surface (broadband radiation); 3) low-mid frequency noise originated from the instabilities in the shear layer inside the cove region. The vortex shedding that usually occurs at low amplitudes is a noise source that contains both dipoles and quadrupoles. The unsteady fluctuations contain dipole sources of sound, and the cove region noise mechanism includes mainly quadrupole sources of noise. To reduce the noise radiation generated by the second mechanism (pressure fluctuations), the effect of visco-elastic coating was investigated. It was found that the level of fluctuations was damped by almost 600 Pa, corresponding to about 3 dB in noise levels.