Hybrid Wing–Body Aircraft Slat Noise

Abstract

This paper presents an analysis of the slat noise for hybrid wing–body aircraft. It is shown that the hybrid wing–body slat noise is characterized by its broad spectral shapes with frequencies depending on both the mean flow velocity and the aircraft angle of attack, with the former following the conventional Strouhal number scaling and the latter explainable by the dependence of the coherence length of the unsteady flows on the angle of attack. Although the overall noise levels approximately follow the fifth power law in Mach number, the Mach number effects manifest themselves spectrally in both amplitudes and spectral shapes. The noise amplitude is shown to also depend on the angle of attack, assuming a minimum in the range of 3 to 5 deg. These features are all modeled and incorporated in slat noise-prediction methodologies, extending the prediction capability from conventional to hybrid wing–body configurations. Comparisons between predictions and data show very good agreements in both various parametric trends and the absolute levels. The hybrid wing–body aircraft is designed to operate at angles of attack higher than those of conventional aircraft. This is shown to significantly increase the hybrid wing–body slat noise. To further illustrate, the test data are extrapolated to full scale and compared with the slat noise of the Boeing 777 aircraft, showing that the former is higher than the latter.