Wake Modification and Noise Emission of Serrated NACA 65(12)-10 at Moderate Reynolds Number

Abstract

Large eddy simulation (LES) with Ffowcs Williams and Hawkings (FW-H) analogy is performed to investigate the flow structure and noise emission of NACA 65(12)-10 aerofoil with and without a serrated trailing-edge at a moderate Reynolds number (Rec=5×105). Following, the noise reduction mechanisms and the noise source regions are analyzed in detail. Results indicate that trailing-edge serrations reduce the overall sound pressure level by up to 6 dB at a 0° direction angle, and the noise reduction mainly occurs at a frequency lower than 10 kHz. The trailing-edge serrations can act as vortex generators and, thus, reorganize the vortex structure, altering the spanwise vortex to a large-scale streamwise vortex. Besides, serrations reduce the magnitude and modify the distribution of the power spectrum density of pressure fluctuation in the near wake, and the spanwise coherence magnitude is decreased. Additionally, the phase interference of acoustic sources at different spanwise positions is enhanced. Wavelet analysis reveals that the hump of the broadband noise spectrum of the serration aerofoil is mainly contributed by the serration tip region. The conclusion provides inspiration for further noise reduction by trailing-edge serrations.