Research on the Noise Reduction Mechanisms of Bionic Airfoils with Different Serrated Trailing-Edge Structures

Abstract

Inspired by the silent flight capability of owls, the serrated trailing-edge design is recognized as an effective method to control trailing-edge interference noise arising from turbulent boundary layers. Based on the NACA0018 airfoil and the serrated structures found in owl wings, this paper designs five different bionic airfoils featuring varying serration heights and spacings. By utilizing large eddy simulation and the Ffowcs Williams-Hawkings acoustic analogy model, we explore the noise reduction mechanism of the serrated trailing edge and validate the accuracy of the numerical methods employed. At an angle of attack of 6°, the study investigates the effects of serration spacing and height on the flow structure near the trailing edge, far-field noise, and noise reduction capabilities of the airfoils. It is found that the serrated trailing edge mitigates the separation of the turbulent boundary layer near the trailing edge, causing separation vortices to shift toward the trailing edge and enabling fluids to adhere more readily to the airfoil surface. This, in turn, reduces noise generated by vortex shedding. As the serration height H increases, the noise reduction effect becomes more pronounced, whereas the effect of serration width L on noise reduction is less distinct. Among the designs, the H2.5L10 and H5L5 airfoils exhibit the best noise reduction performance. Furthermore, acoustic field analysis reveals that the bionic serrations are beneficial in reducing mid-to-low-frequency noise. Through a comprehensive analysis of both flow and acoustic fields, this paper sheds light on the influence of serration parameters on airfoil noise reduction, providing crucial theoretical foundations for noise reduction in large-scale equipment such as axial flow fans and wind turbines.