Reduction of Turbulence Interaction Noise Through Airfoils With Perforated Leading Edges

With the aim of reducing turbulence interaction noise of axial fans, a wind tunnel study was performed on airfoils equipped with a flow permeable leading edge. The leading edges were realized as bulk materials with round pores and manufactured using rapid prototyping. The inflow turbulence was generated by a turbulence grid. Acoustic measurements were performed using microphone array technology, while simultaneously the aerodynamic performance was captured with a wind tunnel balance. In order to provide insight on the flow phenomena at the perforated leading edges, a RANS simulation was performed. The results show that a noticeable noise reduction up to 8 dB is possible in a frequency range between 1 kHz and 4 kHz, while for leading edges with large pores additional high frequency noise is generated. At low geometric angles of attack from 0° to 8°, the aerodynamic performance of the modified airfoils is the same as for a reference airfoil with solid leading edge. At higher angles of attack the perforated leading edges lead to an aerodynamic penalty.