Abstract
A turbulent inflow distorts as it approaches an airfoil's leading edge (LE), which is an important phenomenon influencing the airfoil LE noise. This mechanism is not yet fully understood and is not accounted for in Amiet's theory for LE noise. Thus, the main contribution of this paper is to discuss a possible new approach to account for turbulence distortion in Amiet's LE noise model. The analysis is based on wind tunnel experiments performed for four NACA airfoil geometries. Hot-wire anemometry and a microphone array were used to evaluate the turbulence in the LE region and the radiated noise, respectively. Turbulent inflow was generated with a rod and a grid. Based on the measured turbulence data, a formulation that describes the turbulence length scale near the airfoil LE is introduced, which yields more accurate noise predictions when used in combination with Amiet's model. The proposed approach to estimate LE noise consists of using an appropriate turbulence spectrum formulation for the distorted turbulence and the proposed expression to determine the turbulence length scale near the airfoil LE, yielding a maximum discrepancy between measured and predicted LE noise of 4dB for a rod Strouhal number from 0.3 to 3.
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