Frequency Selection Mechanism of Airfoil Trailing-Edge Noise

摘要

An experimental investigation was conducted with the aim to reveal the frequency-selection mechanism of thenacoustic noise emanated from the trailing edge of two-dimensional airfoils, and a single splitter plate was proposednfor suppressing trailing-edge noise. It was observed that broadband disturbances caused by Tollmien–Schlichtingninstabilities in the transitional boundary layer increase if trailing-edge noise is suppressed with the proposed device.nIn addition, by the introduction of artificial acoustic feedback, for which the initial disturbances are obtained fromansensor for unsteady pressure near the trailing edge, a particular discrete Tollmien–Schlichting wave is selected fromnamong the broadband disturbances caused by Tollmien–Schlichting instabilities. This result demonstrates that thenprocess of frequency selection is clearly ascribable to a positive feedback loop between instabilities in the boundarynlayer and trailing-edge noise. Also, the application of artificial acoustic feedback shows that the airfoil boundarynlayer favors a particular frequency, which results in steplike structures as a function of the distance between thenloudspeaker and the trailing edge that are similarly observed in conventional environments with natural trailing-nedge noise emission.