An experimental investigation into the aerofoil trailing-edge broadband noise reduction using ogee serrations

Trailing edge (TE) serrations have been widely used as an effective technique to reduce the turbulent boundary-layer TE noise. In this paper, an experimental campaign is carried out to study the effects of ogee serrations on TE noise reduction. Serrations are installed on a NACA 0012 aerofoil and tested in an aeroacoustic wind tunnel. Ogee serrations of various geometries are retrofitted to the aerofoil and tested at various flow speeds and angles of attack (AoAs). The geometry of ogee serrations is parametrized by varying serration wavelength (λ), amplitude (2h), and sharpness factor (b). Traditional sawtooth serrations, considered a special case of ogee serration when its sharpness factor approaches zero, are also included. A sensitivity analysis of the TE noise reduction is conducted by varying each geometric parameter of the serrations. Results show that ogee serrations achieve effective noise reduction of 1-3 dB under various flow speeds. With the increase of AoA, the noise reduction gradually diminishes until noise increase occurs at AoA $\ge {15}^{\circ }$. In particular, it is shown that ogee serrations outperform sawtooth serrations when the serration is sufficiently sharp (large 2h, small λ, and large b) at intermediate and high frequencies, in accordance with analytical predictions.