On the turbulence distortion effects for airfoil leading-edge noise prediction

Amiet’s leading-edge noise prediction model estimates the noise generated by the turbulent inflow interacting with the leading-edge (LE) of an airfoil. Although successful in predicting the noise of thin flat plates, Amiet’s model does not account for the real airfoil geometry, resulting in inaccurate noise estimation for these geometries. For real airfoils, turbulence distortion is an important but not entirely understood phenomenon that affects the airfoil radiated noise. This paper discusses the turbulence distortion in the vicinity of an airfoil LE focusing on improving Amiet’s noise prediction. Experiments were performed in the Aeroacoustic Wind Tunnel of the University of Twente. The inflow turbulence was generated by a grid and a circular rod, and it was evaluated in the vicinity of a NACA 0008 airfoil LE using hot-wire anemometry and wall-pressure fluctuation measurements. The chord-based Reynolds number ranged from 2 × 10⁵ to 6.4 × 10⁵ . The rod-airfoil radiated noise was measured and compared with Amiet’s model. Results show that the root-mean-square of the velocity fluctuations, d_{t dt}, and the turbulence integral length scale, d_t, at the stagnation line considerably decreased as the LE is approached. The radiated LE noise predicted by Amiet’s model overestimates the LE noise for high frequencies. However, the predicted LE noise agrees well with the measurements up to a Strouhal number of 10 if the turbulence spectrum based on the rapid distortion theory is used in Amiet’s model, with input the d_{t dt} and d_t values measured close to the airfoil LE. This shows that the turbulence distortion can be accounted for in the LE noise prediction model. This paper also provides empirical expressions for d_{t dt} and d_t in the vicinity of the airfoil LE. These expressions yield more accurate noise predictions for low and high frequencies with Amiet’s method.