Airfoil Trailing-Edge Noise Reduction by Application of Finlets

Abstract

This experimental study investigates the effect of biologically inspired finlets on the reduction of trailing-edge noise of a NACA 0012 airfoil. At a chord-based Reynolds number of 400,000, the far-field noise measurements show that the finlets are capable of reducing the trailing-edge noise effectively from 1000 to 4000 Hz with up to 6 dB reduction, for effective angles of attack from 0 to 8 deg. By correlating the far-field noise to the boundary-layer measurements, an optimal finlet height to boundary-layer thickness ratio to achieve the highest noise reduction is discussed. Static pressure and dynamic pressure fluctuations are examined, particularly within the finlet-treated area, to capture the flow dynamics through the treatments. The unsteady surface pressure fluctuation spectra show strong reduction at frequencies higher than 1000 Hz in the finlet wake, complying with the far-field measurements. Both the auto- and cross-correlation results of the unsteady surface pressure reveal the formation of large-scale turbulence at the entrance and toward the exit of the finlets. Moreover, they suggest that the formation and subsequent mixing of these large-scale structures with the boundary layer can be beneficial to reducing the unsteady surface pressure fluctuations. The findings will be useful to potential optimization of the finlets.