Airfoil Self-Noise Reduction by Gradient Distributed Porous Trailing Edges

Abstract

Porous material–inspired noise reduction has been proved to be an effective method to reduce airfoil self-noise during the last few decades. However, the used porous materials in previous studies generally have homogenous physical properties. In order to obtain higher airfoil self-noise reduction, in this paper, nonhomogenous porous trailing edges are proposed, which feature a piecewise gradient distributed property in pores per inch (ppi). Detailed acoustic measurements performed in the 0.55×0.4-m aeroacoustic wind tunnel showed that the proposed gradient distributed porous trailing edges can achieve a peak noise reduction of up to 43.68 dB and a maximum decrease in overall sound pressure level of up to 19.72 dB, mainly due to the mitigation of vortex-shedding noise of the laminar flow. For turbulent flow, the noise-reduction ability is weakened but can still reduce up to 5.25 dB of turbulent broadband noise. A parameter study of gradient distributed properties on noise reduction revealed several design principles for the proposed modifications, i.e., the porous treatments with larger porous coverage and located at the last 5% chord length of the airfoil gain better noise reduction. Moreover, airfoil self-noise reduction is enhanced when the porous treatments provide a gradual transition from the solid main body to that of the downstream free flow.