Reduction of flow induced tonal noise through leading edge tubercle modifications

Abstract

A sinusoidal modification to the leading edge of an airfoil (tubercles) has led to the elimination of tonal noise for a NACA 0021 airfoil at a Reynolds number, Re ~ 120,000. It has also been found that the overall broadband noise is reduced for a considerable range of frequencies surrounding the peak in tonal noise. Investigations have also revealed that changing the amplitude and spacing between the tubercles has an effect on noise reduction. The mechanism of noise reduction is believed to be strongly related to the formation of streamwise vortices which are generated by tubercles. These vortices most likely have an effect on the stability characteristics of the boundary layer, hence influencing the velocity fluctuations of the shear layer near the trailing edge. In addition, spanwise variations in separation location are thought to affect the vortex shedding process, which could influence the feedback mechanism.