Experimental investigation on aerodynamic noise emissions from airfoils with trailing edge modifications

Abstract

Aerodynamic noise from airfoils is one of the major concerns during flight operations. newlineThe stringent norms laid by the regulatory bodies motivated the researchers to investigate newlinethis field for the past several decades. A dominant aerodynamic noise source in airfoils newlineis the scattering of eddies in the turbulent boundary layer (TBL) at the trailing edge. newlineNumerous passive methods are adopted for the reduction of TBL noise by modifying the newlineeffectiveness of eddy scattering at the trailing edge and disintegrating the coherent newlinestructures. In the present thesis, the aerodynamic noise characteristics by passively newlinemodifying the trailing edge configurations in airfoils are experimentally investigated. newlineThe airfoil models used in the study are thin airfoil, NACA 0012, NACA 0018, and newlineNACA 6412. The acoustic measurements are carried out in an in-house fabricated open newlinejet anechoic wind tunnel test facility having a cut-off frequency of 300 Hz. All the airfoils newlinehave a chord length (c) of 150 mm. The freestream jet velocity (Uand#8734;) varies between 20 newlinem/s to 53 m/s, and the corresponding Reynolds numbers (Rec) based on the airfoil chord newlinerange between 2 × 105 newlineand 6 × 105 newline. The geometric angles of attack considered are in the newlinerange of 0 to 15 degrees. The preliminary experimental results on thin and NACA airfoils newlinedepict that the noise levels from the thin airfoil are higher in the entire frequency range newlineat all the Reynolds numbers. Further, noise emissions from a thin airfoil decrease with newlinean increase in the angle of attack. However, for NACA 0018, the noise levels increase newlinewith the angle of attack, while they remain unchanged for NACA 0012. For subsequent newlinestudies, the passive modifications considered at the trailing edge of the airfoils are as newlinefollows. (i) A line distribution of holes adjacent to the trailing edge, (ii) perforated newlineextensions at the trailing edge, and (iii) trailing edge serrations with different root newlinegeometries.