Comparative investigation of airfoil noise reduction using bio-inspired trailing-edge serrations

The noise reduction ability of the trailing-edge serrations inspired by owl wings has been extensively recognized in fields such as blade type fluid machinery, which is often applied in aviation engines, wind turbines, air conditioners, etc. According to the previous study on the aerodynamic noise of non-smooth biomimetic blades, the noise reduction capacity of different serration shapes exhibits different performances. Therefore, the noise reduction potential of biomimetic trailing edges is worth further exploration to achieve the challenge of developing low-noise fluid machinery and break the limitations of current biomimetic design for noise reduction. The ability of the airfoil with five different curvature serrations to suppress aerodynamic noise is evaluated by using the hybrid computational aeroacoustics method. The results demonstrate that the airfoil with iron-shaped serrations behaves with excellent performance on noise suppression and the overall sound pressure level reduction of up to 13.3 dB is achieved. Based on vortex sound theory, iron-shaped serrations are beneficial for maximizing the dissipation of the strong sound waves to radiate energy outward generated by the periodic shedding of the tubular vortex streets of the smooth airfoil. Furthermore, the noise reduction ability of the airfoil with convex-curvature serrations commonly performs better than that of the airfoil with concave-curvature serrations. The destructive interference generated by the strong shear forces for convex-curvature serrations is responsible for inducing the more intense energy dissipation and decoherence effects along with the spanwise direction.