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Description
This work investigates the sound field produced when a point source interacts with the trailing edge of an airfoil, modeled as a half-plane. A newly presented Green’s function for sound diffraction by infinitely long and finite-length diffracting edges is employed. First, it is shown that the diffracted field dominates the total sound field, when the source is on the airfoil surface or very close to the trailing edge. An equation is presented that provides, a priori, the relative importance of the diffracted field in the total sound field. Second, the solution is modified to predict the diffracted field around serrated edges and the geometrical acoustics field is added to compute the total field. Next, the premise that serrated trailing edges offer advanced noise mitigation compared to straight edges is tested. Serration profiles with varying segment lengths and inclination angles are compared to the corresponding straight-edge profiles on various receiver planes and for different source locations (modeling the location of different noise sources such as jet noise or airfoil self-noise). Serrated profiles offer increased noise protection (compared to straight-edge profiles) to some receivers, but reduced protection to others. The optimal serration profile that maximizes the overall noise reduction on a receiver plane depends on source location and receiver plane. However, a serration profile with segment length of 1.5 wavelengths and a 75-degrees inclination angle performs well in most cases. The benefits of serrated edges are maximized in the airfoil’s shadow zone, except when the source is at the trailing edge itself.