A Study of the Sources of Slat Noise using Proper Orthogonal Decomposition

Abstract

Airframe noise is already a barrier in the expansion of commercial aviation. Among airframe noise sources, the leading-edge slats play an important role since it is a source distributed along almost the whole wingspan. Although the high-frequency tonal peak is already known to be generated by trailing-edge vortex shedding, the origin of other elements of the spectrum of slat noise is not fully understood yet. The present work considers an unsteady Lattice-Boltzmann simulation of the flow around a typical threeelement high-lift configuration, and performs an analysis of the flow structures existing inside of the slat cove at the peak frequencies of the far-field noise radiation. Proper orthogonal decomposition (POD), widely used in the identification of coherent structures in turbulent flows, is employed here in order to filter out the fluctuations without a significant correlation on the slat cove region.i Different inner products are investigated in the POD formulation, using not only the most standard turbulent kinetic energy norm but also pressure norms, more adequate to the study of noise generation phenomena. The results show that, at the dominant tonal peaks, the flow inside the cove is dominated by vortical structures generated by the inflectional instability of the mixing-layer.