Aerodynamic noise characteristics of a thin airfoil with line distribution of holes adjacent to the trailing edge

Abstract

This paper investigates the noise emissions from thin airfoils experimentally. An attempt has been made to study the effect of line distribution of 3 mm diameter holes adjacent to the trailing edge on noise emission characteristics. Thin airfoils having chord length and span of 150 and 240 mm, respectively, are considered for the investigation. The airfoil is subjected to the flow Reynolds number (defined based on the chord length of airfoil) in the range of 2.0 × 10⁵ to 5.0 × 10⁵, and angles of attack of 0°, 2°, and 4°. The spectral results indicate that the modified airfoil with holes is effective in minimizing the lower frequency noise (<3.5 kHz) compared to that of the reference airfoil. The reduction in the low-frequency sound pressure levels for the modified airfoil is found up to 5 dB. The modified airfoil with holes is ineffective in reducing the higher frequency noise components, and in fact, generated a broadband frequency noise at higher Reynolds number. From the spectral studies, a critical Strouhal number is estimated to be around 0.15 that defines the limiting value for the effectiveness of the modified airfoil. The overall sound pressure level studies depicted that the modified airfoil is effective at higher angles of attack with the reduction of around 1–2 dB. The noise generated from the thin airfoils is found to have the directivity towards the upstream.

Keywords

Aerodynamic noise thin airfoil trailing edge modification holes distribution acoustic directivity

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