Trailing edge noise reduction using bio-inspired finlets

Abstract

Inspired by the silent flight of the owl, the current work focuses on the reduction of trailing edge noise using 2D finlets. Overset-Large Eddy Simulations are carried out of two configurations, (i) the baseline configuration consisting of a NACA0012 airfoil and (ii) an identical configuration, however, now with finlets installed near the trailing edge. The considered chord based Reynolds number Rec equals 4.2×105 for a non-zero angle of attack α of 4°. The resulting turbulence statistics in the boundary layer and the power spectral density (PSD) spectrum of the surface pressure fluctuations show good agreement with the experimental data. Detailed analysis of the unsteady flow data revealed various noise reduction mechanisms for the here considered case. Firstly, finlets provide a ‘lifting-up’ effect for the most energetic eddies in the boundary layer, which prolongs downstream of the finlets. As a result, the edge scattering is significantly weakened. Secondly, the finlets mounted on the airfoil provide an additional wetted area to the flow which in-turn has a dissipating effect on the surface pressure fluctuations, thereby again weakening the edge scattering phenomena. A reduction in the flow velocity is observed for the flow exiting the finlets channel and towards the trailing edge, which also has a favourable effect in reducing the trailing-edge noise. Finally, a marginal breakdown of the span-wise coherent length scale for frequencies between 2.5 kHz to 9 kHz is also observed.