Acoustic resonances in a 2D high lift configuration

Abstract

Acoustic resonances are computed numerically for a generic two-dimensional high lift configuration. High lift devices are known to be a major source of tonal airframe noise. The computations are made for zero mean flow using a high-order finite element code in conjunction with Perfectly Matched Layer (PML) absorbing boundary conditions. Whatever the actual source of the observed discrete tones is, these tones may be enhanced by or lock onto resonant acoustic frequencies. Our computed resonant frequencies are indeed fairly close to experimentally observed low-frequency slat tones and may be interpreted as resonances of leaky surface waves. These low-frequency resonances are practically unaffected by changes in slat cove geometry contrary to high-frequency resonances.