Aerofoil trailing edge self-noise reduction by Surface Mounted Attenuation Devices

Abstract

This paper presents the results of a preliminary experimental study into the effect of add-on type finlets on the aeroacoustic performance of a wind turbine aerofoil. The content mainly deals with the turbulent boundary layer - trailing edge broadband noise characteristics subjected to the add-on finlets. The test program seeks to test various combinations of finlet height and spacing present on the (1) suction side only, (2) pressure side only, and (3) both suction and pressure sides. Each finlet parameter configuration is tested at jet velocity U=30m/s and 45m/s, at geometric angles of attack AOA (Angle of Attack) (geometric) = 10°, 0°, -10°. Based on the data acquired thus far it is observed that a finlet usually performs best with increasing height and decreasing spacing. Under configurations (1) and (2), finlets are able to produce up to 2dB Sound Power Level broadband noise reductions, where configuration (3) offers broadband reductions of up to 7dB Sound Power Level, with potential to observe more reductions once optimised. The main parameter for improved performance of finlets is the spacing rather than the height. Finlet height does not offer significant impact on the performance if the spacing is not optimal. The established trend for optimal finlet parameters remains consistent for all AOA, offering improved performance at high positive angles, which has a practical application to wind turbine blades.