Effect of wavy leading edges on airfoil tonal noise

Abstract

This work presents numerical studies on the effect of wavy leading edges on airfoil instability tonal noise. Large eddy simulations are conducted for NACA0012 (National Advisory Committee for Aeronautics) airfoils with straight and wavy leading edges. The far-field aerodynamic noise is predicted using the Ffowcs Williams and Hawkings acoustic analogy theory. The inflow Mach number is approximately 0.17 with an angle of attack of 4.3°, and the chord based Reynolds number is 600 000. The present numerical method is first validated by existing numerical results and a semi-empirical model for the straight baseline airfoil. Then, the effects of wavy leading edges on the aerodynamic performance, aeroacoustic performance, and noise reduction mechanisms are discussed in detail. The wavy leading edge is found to be detrimental to the mean aerodynamic performance with a decreased lift and increased drag. However, the lift fluctuations are significantly reduced. The instability tonal noise and its harmonic are totally removed by the wavy leading edges, while an extra broadband hump appears at the middle frequency. The low frequency and high frequency noise are also increased by the wavy airfoil. The laminar separation bubble is removed, and the flow separation is decreased by the wavy airfoil in the vicinity of the trailing edge. The pressure fluctuations around the trailing-edge are considerably diminished, and the spanwise coherence spectra are also significantly reduced by the wavy airfoil. Furthermore, it is noteworthy that the coherence reduction spectrum at the source is almost consistent with the far-field noise reduction spectrum.