Aeroacoustic measurements of slat noise on a three-dimensional high-lift system

Abstract

Experimental results are presented for the aerodynamics and acoustics of an unswept wing with a half-span flap and a full-span slat. Concurrent aerodynamic and acoustic measurements were obtained for high-lift riggings representative of landing-approach configurations. Phased microphone array measurements indicate that slat gap noise is most significant for high slat deflections where the slat is lightly loaded. More specifically, the peak noise level for the 25deg slat deflection was 20 dB higher than that of the 9-deg slat deflection. Measurements of intermediate angles indicate a gradual decrease in slat noise as slat deflection is decreased. Strouhal frequency scaling of the 25deg slat configuration suggests that vortex shedding from the slat trailing edge may be an important noise mechanism. However, a non-linear relationship between slat noise level and angle of attack suggests a more complex phenomenon. Computational results detail the strength of the shear layers in the slatcove flow field. Variations in the slat-cove shear layers with slat deflection and angle of attack are presented. From correlations between the computed results and the measured acoustics, it is hypothesized that a KelvinHelmholtz instability develops in the slat cove and a feedback mechanism forms between the slat-cove and slat trailing-edge flow fields.