Nonflat-Plate Transition-Serrated Trailing Edge for Airfoil Self-Noise Reduction

Trailing-edge noise is the primary source of airfoil self-noise. Nonflat-plate serrated trailing edge can suppress the broadband trailing-edge noise at high frequencies, while the overall noise reduction is compromised by low-frequency narrowband bluntness-induced noise at the sawtooth root. In this paper, a nonflat-plate transition-serrated trailing edge is proposed to reduce the bluntness-induced noise. The configuration uses a wedge-shaped transition structure within the sawtooth gap to eliminate the bluntness noise. Firstly, the appropriate parameters of the transition structure are determined by numerical simulation. Then, optimal configuration is employed for test verification. Finally, the noise reduction mechanism of the configuration with the best noise reduction is analyzed. Simulation results indicate that the configuration can accelerate the fragmentation of large-scale spanwise vortices at sawtooth root, weakening the vortex shedding noise. Moreover, compared with the nonflat-plate serrated trailing edge, it forms counter-rotating oblique vortices at a position further forward within the sawtooth gap, promoting transverse flow, thereby reducing broadband noise over most frequencies. Experimental results show that the configuration with an appropriate transition structure can afford the highest reduction of 27.2 dB for the bluntness-induced noise and 5.7 dB for the trailing-edge noise.