Numerical and experimental investigation of propeller noise with trailing-edge serrations

Abstract

The present study examines the effect of trailing-edge serrations on propeller noise at both hover and forward flight conditions. Three different serrations were designed with wavelengthto-amplitude ratios from 0.6 to 1.2, based on the several recent literature. Both experimental measurement and numerical simulations were carried out to first quantify the far-field noise spectra and subsequently, to provide flow field analyses, which can shed some lights on the physical mechanisms leading to the noise reduction at different operating conditions. The results show that the present unsteady RANS simulation predicts the far-field acoustics of both the baseline and serrated propellers, which agree relatively well with the experimental measurements at hover conditions. However, due to limited simulation time, the blade pass frequencies and its harmonics are not well captured. Moreover, the use of trailing-edge serrations on propellers lead to clear reduction of the far-field noise levels, and the effectiveness of the noise reduction is dependent on the key parameters defining the serrations as well as the propeller operating condition. With the serrations, the turbulent kinetic energy over the entire blade reduces, particularly close to the trailing-edge regions and the iso-surface contours reveal that the turbulent structures become less coherent in the blade spanwise direction. Subsequently, these turbulent structures are observed to decay more rapidly than the baseline configuration in the near-wake region. These modifications to the turbulent structures on the blade as well as in the near-wake possibly contributes the reduction of far-field noise by applying trailing-edge serrations to the propellers.