On Detrimental Effects of Excrescences on the Slat Noise

Abstract

In airplane landing the slat noise is already a barrier to the development of quieter commercial airplanes. Investigations have been made by several research groups to understand the mechanism of noise generation in slat and develop better tools to predict it. Most of the published works related to slat noise considers clean idealized geometries, whereas real slats contain some imperfections to enable its operation. The in uence of a protrusion on the slat cavity surface on the unsteady ow around the slat and on the propagated sound was here investigated via numerical calculation. The protrusion was a sealing device to avoid metal-metal contact. Lattice-Boltzmann method was used in the computations. The e ect of the seal on the mean surface pressure distribution is limited to the region close to it. When the seal is positioned inside the recirculation zone, the region next to the cusp present less uctuation intensity and the vortices formed in the mixing layer keep two-dimesionality for a longer distance in the way to the reattachment point. The noise propagated to fareld also present more intense low frequency tonal peaks. Although discretization as ne was 0:15mm was employed, uctuations of a speci c frequency band were still mesh dependent.