Experimental and predicted leading- and trailing-edge noise of symmetric airfoils under zero mean-loading

Abstract

Incorporating the effect of airfoil geometry in airfoil noise prediction methods is paramount to designing silent wind turbines and achieving regulation limits. However, the airfoil geometry effect on the leading- and trailing-edge noise has not been fully understood. To address this, our research uses a phased microphone array to measure the leading- and trailing-edge noise of airfoils NACA 0012, 00018, 0008, and 63018, which have different chord lengths. The inflow turbulence is generated by a rod located upstream of the airfoils. The far-field noise is compared with Amiet's theory for both noise sources. The results show that the leading-edge noise reduces with the leading-edge radius and maximum thickness in the high- and mid-frequency ranges, respectively. Scaling laws based on these geometric parameters are proposed. The trailing-edge noise of the several airfoils was compared at several velocities and Reynolds numbers. Scaling laws using these quantities were proposed for each case. Furthermore, the competition of leading- and trailing-edge noise mechanisms are assessed when airfoils are subjected to inflow turbulence. The dominant noise source varies in function of the airfoil geometry and frequency. The inflow turbulence increases the trailing-edge noise of the different airfoils. Furthermore, it dominates in a larger frequency range for the thickest airfoil.