An experimental study of the noise resulting from the interaction of an airfoil with incident turbulence is presented. The test models include NACA0015 airfoils of different chord lengths, a flat plate with a sharp leading edge, and an airfoil of same section as a reference Fowler flap. The airfoils are immersed in nearly isotropic turbulence. Two approaches for performing the noise measurements are used and compared. The effects that turbulence intensity and integral length scales, airfoil geometry, velocity and angle of attack have on the incident turbulence interaction noise are examined. Detailed directivity measurements are presented. It is found that noise spectral levels beyond the peak frequency decrease at a slower rate for the sharper airfoil leading edges, and that spectral peak level (at 0° angle of attack) appears to be mostly controlled by the airfoil's thickness and chord. Increase in turbulence integral scale and intensity are observed to lead to a uniform increase of the noise spectral levels with an LI~2 dependence (where L is the turbulence longitudinal integral scale and I is the turbulence intensity). Noise levels are found to scale with the 6th power of velocity and the 2nd power of the airfoil chord. Sensitivity to changes in angle of attack appears to have a turbulence longitudinal integral scale to chord (C) ratio dependence, with large effects on noise for L/C ≥ 1 and decreased effects as L/C becomes smaller than 1. For all L/C values, the directivity pattern of the noise resulting from the incident turbulence is seen to remain symmetric with respect to the direction of the mean flow until stall, at which point, the directivity becomes symmetric with respect to the airfoil chord. It is also observed that sensitivity to angle of attack changes is more pronounced on the model suction side than on the model pressure side, and in the higher frequency range of the spectra for the largest airfoils tested (L/C < 0.24).
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机译：对翼型与入射湍流相互作用产生的噪声进行了实验研究。测试模型包括不同弦长的NACA0015机翼，具有锋利前缘的平板以及与参考Fowler襟翼相同截面的机翼。机翼浸入几乎各向同性的湍流中。使用和比较了两种执行噪声测量的方法。研究了湍流强度和整体长度尺度，机翼几何形状，速度和攻角对入射湍流相互作用噪声的影响。给出了详细的方向性测量。已经发现，对于尖锐的机翼前缘，超出峰值频率的噪声频谱水平以较慢的速率降低，并且频谱峰值水平（在0°迎角处）似乎主要由机翼的厚度和弦控制。观察到湍流积分尺度和强度的增加导致噪声频谱水平的均匀增加，且依赖于LI〜2（其中L是湍流纵向积分尺度，而I是湍流强度）。发现噪声水平与速度的六次方和机翼弦的第二次方成比例。对迎角变化的敏感性似乎与湍流纵向积分标度和弦（C）比率有关，对于L / C≥1的噪声影响很大，而当L / C小于1时，影响减小。 C值表示入射湍流产生的噪声的方向性图相对于平均流方向保持对称，直到失速为止，此时，方向性相对于翼型弦变得对称。还可以观察到，在模型吸力侧，对迎角变化的敏感性比在模型压力侧，以及在测试的最大翼型的光谱的更高频率范围内，更明显（L / C <0.24）。
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