Effect of Slat Gap on Farfield Radiated Noise and Correlation with Local Flow Characteristics

Abstract

Significant source noise reduction efforts are needed to cope with the "Visions 2020" of the "group of personalities" in Europe. This vision defines an aircraft noise reduction goal of 15 dB per operation until 2020, which inherently requires a reduction of airframe noise, and thus of high lift devices noise, by this same amount during landing approach. Since high lift devices noise is known to be dominant by slat noise, the aerodynamic optimization of slat-wing configurations must also account for noise aspects. Therefore the effect of slat gap variations on slat noise generation was investigated through a scale model high lift devices experimental wind tunnel study. In parallel CFD calculations (2D RANS) were performed for all test configurations to correlate measured slat noise characteristics with flow field data. Broadband slat noise levels were found to scale best with the local flow velocity at the pressure (cove) side close to the upper slat trailing-edge. Relative to the reference slat gap width a broadband noise reduction of up to 10 dB was achieved for reduced gap width (up to 15%), accompanied by an up to 4% degradation in maximum lift. For high angles-of-attack slat noise spectra were governed by a complex tone pattern, which do not follow a simple harmonic scheme but approximately scale with inflow velocity.