Experimental and numerical study on noise reduction of airfoil with the bioinspired ridge-like structure

Abstract

In general, the serrated blade edge can reduce the aeroacoustic noise of the thin airfoil, but the blade's integrity and pneumatic efficiency cannot be guaranteed. This research proposes a bioinspired ridge-like structure that won't affect the strength of the blade, and it has more potential to be employed as an innovative noise reduction configuration for engineering applications. The experimental data shows a significant peak noise reduction of nearly 26 dB and a magnitude decrease of more than 10 dB in the overall sound pressure level (OASPL) at a freestream velocity of 20 m/s with the attack angle 0˚. Based on the computational fluid dynamic simulation, the mechanism for the noise reduction employing the ridge-like structure is qualitatively and quantitatively examined. In summary, the ridge-like structures on the leading edge may enhance the transition to move an upstream position. Under the synergy of the ridge-like structures on the leading and trailing edges, the turbulent kinetic energy (TKE) value close to the airfoil surface is reduced, and the spanwise coherence of the surface pressure fluctuation source weakens. The phase spectra analysis indicates that the phases of the fluctuation pressure signals beside the center of the two adjacent ridge-like structures are opposite, and therefore the phase interference in the biomimetic airfoil between two adjacent ridge-like structures is significantly enhanced in the frequency range from 100 Hz to 800 Hz. For the biomimetic airfoil described in this paper, the phase interference between adjacent ridge-like structures immediately results in noise.