Numerical Investigation of Wavy Leading Edges on Rod-Airfoil Interaction Noise

A hybrid computational aeroacoustics method is applied to investigate the effect of wavy leading edges on rod-airfoil interaction noise. The flow field is solved by an incompressible large-eddy simulation. The acoustic far-field is predicted using the Ffowcs Williams and Hawkings acoustic analogy. NACA 0012 airfoils with straight and wavy leading edges (denoted by SLE and WLE, respectively) are located one chord downstream of a circular rod. The free-stream Mach number is 0.2 and the Reynolds number based on the rod diameter is 48,000. The present numerical method is first validated by existing experimental and numerical results for the SLE case. Then, both the sound pressure level and sound power level of the SLE and WLE cases are computed to assess the noise reduction effect. A considerable noise reduction level is obtained in the mid- to high-frequency range. The main noise reduction mechanisms of the WLE are investigated in detail. The surface pressure fluctuations along the leading edge of the WLE airfoil exhibit a significant attenuation compared with the SLE counterpart, which leads to reduced sound source levels. It is also found that there exist spanwise decorrelation and decoherence effects along the leading edge of the WLE case, which means a noise reduction effect according to Amiet's theory. Phase interference effect is also found along the WLE geometry and this effect is conjectured to be a more essential noise reduction mechanism, because the trends of the phase-shift spectrum are almost consistent with the noise-reduction spectrum.