Identification of the two-sources at the aircraft slat/fuselage juncture based on phased array

Abstract

Slat/fuselage juncture noise or slat horn noise has been identified as a major airframe noise component and is commonly assumed to be similar to the flap side-edge noise. However, whether the slat/fuselage juncture noise has similar characteristics to flap side-edge noise has not been confirmed. In this study, the slat/fuselage juncture noise sources in realistic aircraft configurations are investigated based on phased microphone arrays. Two different source mapping methods of L1/2-DAMAS and CLEAN-SC are applied to the airframe noise benchmark test DLR1 for cross validation. It is shown that both methods obtained identical noise characteristics and source strength distributions. The slat/fuselage juncture noise is revealed to be completely different from the flap side-edge noise. The spectrum of the slat/fuselage juncture noise is Helmholtz-dependent, rather than Strouhal-dependent, as the flow Mach number increases. The broad peak of the spectrum shifts towards a higher frequency as the angle of attack increases. Furthermore, both the two source mapping methods all identified two noise sources existing at the aircraft slat/fuselage juncture. The first noise source is the inboard slat side-edge vortex scattering and the second noise source is the horseshoe vortex on the fuselage. It is demonstrated that the side-edge vortex scattering dominates the spectrum, especially in the middle- and high-frequency domains. The horseshoe vortex is a major noise contributor in the low-frequency domain. These findings provide improved insight into the underlying noise generation mechanisms and can help develop prediction methods for slat/fuselage juncture flow noise.