Turbulence distortion effects for leading-edge noise prediction

Leading-edge noise is the dominant noise source for applications such as propellers and fans. Amiet's leading-edge noise model is widely used to predict this noise source during the design for these applications. However, Amiet's model is based on an infinitely thin flat plate assumption, not accounting for real airfoil geometric effects, resulting in inaccurate noise estimation for airfoils. The leading-edge noise is mainly affected by the turbulence distortion caused by the airfoil blocking effect due to its finite thickness. This paper discusses the turbulence distortion caused by different airfoil geometries and how to account for turbulence distortion in Amiet's model. Experiments were performed in the Aeroacoustic Wind Tunnel of the University of Twente. The inflow turbulence was generated by a rod. The airfoil geometries tested were NACA0008, NACA0012, and NACA0018. The inflow turbulence distortion was measured in the vicinity of the airfoil leading edge by hot-wire anemometry. In addition, the noise radiated by rod-airfoil interaction was measured and compared with Amiet's noise prediction model. The results show that the velocity fluctuations and turbulence length scale at the stagnation line decreased in the vicinity of the airfoil leading edge. Amiet's model overestimates the leading-edge noise for high frequencies. The predicted leading-edge noise agrees well with the measurements when the turbulence distortion is taken into account in the turbulence spectrum formulation and in the input values of the root-mean-square of the velocity fluctuations and the turbulence length scale. Thus, Amiet's leading-edge noise prediction model can be corrected to account for the turbulence distortion.