Abstract Airfoils generate intensive laminar boundary layer instability noise at low-to-moderate Reynolds numbers. Experimental studies are conducted to investigate the noise radiation characteristics of a NACA 0012 airfoil operated at various angles of attack and Reynolds numbers. It is found that the instability noise changes from a broadband hump to intensive tonal noise with increasing angle of attack, while it changes from tonal noise to a broadband hump with increasing Reynolds number. The overall sound power is observed to follow the 3rd power of the inflow velocity. In addition, wavy leading edges are employed to reduce the instability noise. The wavy leading edges are in the form of sinusoidal profiles with two main design parameters of serration amplitude and wavelength. Parametric studies of the amplitude and wavelength are performed to understand the effect wavy leading edges on noise reduction. It is observed that the sound power reduction level is sensitive to both the amplitude and wavelength. Overall, the wavy leading edge with a large amplitude and small wavelength can achieve the most considerable noise reduction effect.

中文翻译：

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波浪形前缘翼型失稳噪声的实验研究

摘要 翼型在低到中等雷诺数下会产生强烈的层流边界层不稳定噪声。进行了实验研究以研究在不同攻角和雷诺数下运行的 NACA 0012 翼型的噪声辐射特性。发现随着攻角的增加，不稳定噪声从宽带驼峰转变为强音调噪声，而随着雷诺数的增加，不稳定噪声从音调噪声转变为宽带驼峰。观察到总声功率遵循流入速度的 3 次方。此外，采用波浪形前缘来降低不稳定噪声。波浪形前沿呈正弦曲线形式，具有锯齿幅度和波长两个主要设计参数。执行幅度和波长的参数研究以了解波状前沿对降噪的影响。据观察，声功率降低水平对振幅和波长都很敏感。总体而言，幅度大、波长小的波浪形前沿可以达到最可观的降噪效果。