Noise characteristic of the nacelle/pylon/slat juncture in a realistic high-lift aircraft configuration

Abstract

The leading-edge slat is an important contributor to airframe noise. Recent studies revealed that the leading-edge slat in realistic high-lift aircraft configurations forms a more complex nacelle/pylon vortex system, resulting in an intense noise source. Thus, this study investigated the noise characteristics of leading-edge slats in realistic aircraft configurations based on phased microphone arrays. The non-negative L1/2 regularization method for the deconvolution approach for the mapping of acoustic sources (DAMAS) was applied to the airframe noise benchmark test DLR1. An uneven and concentrated source strength distribution around the nacelle/pylon/slat juncture region was obtained owing to the three-dimensional flow pattern. Thus, the leading-edge region was partitioned into small sub-regions to extract the nacelle/pylon/slat juncture noise source. The angle of attack (AoA) has different effects on the slat and nacelle/pylon/slat juncture noises. In detail, the minimum amplitude of the slat noise was obtained at AoA = 5°. In contrast, the amplitude of the nacelle/pylon/slat juncture noise increased as the AoA increased, especially at a high AoAs. The significant increase in the amplitude of the nacelle/pylon/slat juncture noise was mainly attributed to the large increase in the spectrum at the low-frequency range with the increase in the AoA. In addition, the amplitude levels of the slat and nacelle/pylon/slat juncture noises approximately follow the fifth power law of the Mach number with their spectra following a similar scaling law. Both noise spectra followed the Strouhal number scaling laws in the low-frequency range and Helmholtz number scaling law in the high-frequency range. However, both noise sources have different noise generation mechanisms. The revealed noise characteristics are helpful for establishing a physics-based nacelle/pylon/slat juncture noise prediction model and subsequently, the development of noise reduction technologies.