Noise Reduction and Aerodynamics of Airfoils with Porous Trailing Edges

The application of open-porous materials is one possible method to reduce the aerodynamic noise of an airfoil. Depending on the exact location and extent of the porous region, it enables the reduction of trailing edge noise or of noise from the leading edge when subject to inflow turbulence. However, the porous consistency may have a negative effect on the aerodynamic performance of the airfoil, since very often the lift is decreased while the drag increases. In a recent investigation, the generation of trailing edge noise of a set of airfoil models made from different porous materials was examined experimentally. The materials were characterized by their air flow resistivity. Besides the material, the chordwise extent of the porous material was varied. Acoustic measurements were performed in an open jet wind tunnel using microphone array technology, while the aerodynamic performance was measured simultaneously using a six-component balance. In general, both the air flow resistivity and the extent of the porous material have an influence on the trailing edge noise. However, if a suitable material is chosen, the results show that a noticeable reduction of trailing edge noise is possible even with only a small extent of the porous material.