Experimental investigation into the acoustical superiority of ogee serrations in reducing leading edge noise

An experiment is conducted to study the leading-edge noise reduction characteristics of ogee serrations and their performance compared to conventional serrations under various operating conditions in an aeroacoustic wind tunnel. Both the acoustic source contours and far-field noise spectra are examined. It is shown that ogee serrations are superior to the conventional sawtooth serrations within the entire frequency range of interest under all the Reynolds numbers tested in the experiment. It is found that the noise from the turbulence grid used to generate the required inflow turbulence becomes important when the frequency is close to and above 2 kHz, and therefore must be excluded in the examination of the leading-edge noise spectra. In addition to their effect on turbulence interaction noise, it is shown that the use of ogee serrations may result in weaker trailing-edge noise than that of sawtooth serrations at certain frequencies. The additional noise reduction due to the use of ogee serrations generally increases as lambda, the wavelength of the serration, decreases. Furthermore, like sawtooth serrations, the total noise reduction also increases as the lambda decreases. Narrow ogee serrations therefore prove to be more desirable when used for reducing leading-edge noise.