Trailing Edge Noise of Partially Porous Airfoils

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The use of porous trailing edges is one possible approach to reduce airfoil trailing edge noise. Past experiments on fully porous airfoil models showed that a noticeable noise reduction can be achieved. However, this reduction is accompanied by a loss in aerodynamic performance. To combine the acoustic advantages of the porous trailing edge with the aerodynamic advantages of a non-porous airfoil, the generation of trailing edge noise of airfoil models that only have a porous trailing edge is investigated. To this end, initial experiments were performed on a set of airfoils with porous trailing edges of varying chordwise extent in an open jet wind tunnel, using microphone array measurement technique and a deconvolution beamforming algorithm. The lift forces and drag forces were measured simultaneously to the acoustic measurements. Additionally, hot-wire measurements were performed to allow conclusions on the underlying mechanisms that enable the noise reduction. It could be demonstrated that, depending on the porous material, airfoils that are non-porous except for their trailing edge can still lead to a noticeable trailing edge noise reduction, while providing a better aerodynamic performance.