Abstract
As a bionic flow control structure, leading-edge serrations have been proven to effectively suppress the aerodynamic noise of airfoils. Compared with single-wavelength serrations, a greater noise reduction potential can be obtained for airfoils with the double-wavelength serrations because of the phase interference at different tip-to-root ratios. In this study, in order to reduce the aerodynamic noise of a flat plate operating in a steady uniform flow, double-wavelength leading-edge serrations based on Ayton's analytical model are optimized by the meta-heuristic optimization algorithm. The effects of different double-wavelength serrations on the noise characteristics of the flat plate are investigated. By comparing and analyzing the radiation integral function and quantifying the sound pressure along the leading edge of the flat plate, the local source cut-off effect resulting from the large transition curvature of the root and phase difference superposition is analyzed in detail. The results show that, before the first inflection point, the convex sinusoidal and iron-shaped serrations can significantly reduce the aerodynamic noise of the flat plate. When the concave ogee-shaped serrations are adopted, the reduction of the high-frequency noise is more obviously. Especially when the slits are embedded at the roots of the optimized leading-edge serrated structures, the improved design further promotes an additional noise reduction level of 0.7 dB for the flat plate. Through numerical studies, the coupled noise reduction mechanism of the serration roots and the slits is also revealed.