尾缘锯齿结构对叶片边界层不稳定噪声的影响

实验研究了不同雷诺数（2×10⁵~8×10⁵）、不同攻角状态下，3种相同波长（4%弦长）不同振幅（分别为5%、10%、15%弦长）尾缘锯齿结构对叶片层流边界层不稳定噪声的影响。研究表明，在0°攻角状态下，尾缘锯齿会增强甚至诱导产生新的不稳定噪声，显著增大叶片自噪声；在大攻角状态下，尾缘锯齿会减弱甚至完全抑制不稳定噪声，降噪量高达40 dB，降噪机制在于尾缘锯齿结构破坏了不稳定噪声产生所需的声学反馈回路。尾缘锯齿会降低不稳定噪声频率，且锯齿振幅越大，不稳定噪声频率越低。

Blade boundary layer instability noise with trailing edge serrations

The effect of three trailing edge serrations of the same wavelength (4% of the chord length) and different amplitudes (5%, 10% and 15% of the chord length) on blade laminar boundary layer instability noise is investigated experimentally at low to moderate Reynolds number (2×10⁵-8×10⁵) and different angle of attacks. It can be concluded that at zero angle of attack, trailing edge serrations can reinforce or even induce boundary layer instability noise to lead to an increase of the blade self-noise. At larger angle of attack, instability noise is reduced or even totally suppressed by the trailing edge serrations, resulting in a maximum noise reduction of 40 dB. The noise reduction mechanism can be attributed to the destruction of the acoustic feed-back loop, which is essential for the generation of instability noise, by the trailing edge serrations. Trailing edge serrations will decrease the instability tonal noise frequency, and the instability noise frequency is lower with larger serration amplitude.