Experimental study of airfoil instability noise with wavy leading edges

Abstract

Airfoils generate intensive laminar boundary layer instability noise at low-to-moderate Reynolds numbers. Experimental studies are conducted to investigate the noise radiation characteristics of a NACA 0012 airfoil operated at various angles of attack and Reynolds numbers. It is found that the instability noise changes from a broadband hump to intensive tonal noise with increasing angle of attack, while it changes from tonal noise to a broadband hump with increasing Reynolds number. The overall sound power is observed to follow the 3rd power of the inflow velocity. In addition, wavy leading edges are employed to reduce the instability noise. The wavy leading edges are in the form of sinusoidal profiles with two main design parameters of serration amplitude and wavelength. Parametric studies of the amplitude and wavelength are performed to understand the effect wavy leading edges on noise reduction. It is observed that the sound power reduction level is sensitive to both the amplitude and wavelength. Overall, the wavy leading edge with a large amplitude and small wavelength can achieve the most considerable noise reduction effect.