On the leading edge noise and aerodynamics of thin aerofoil subjected to the straight and curved serrations
On the leading edge noise and aerodynamics of thin aerofoil subjected to the straight and curved serrations
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DOI：
10.1016/j.jsv.2018.02.038
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发表时间：
2018-07
影响因子：
4.7
通讯作者：
A. Juknevicius;T. Chong
中科院分区：
文献类型：
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作者：
A. Juknevicius;T. Chong
本文介绍了附加式前缘锯齿对对称NACA 0008翼型气动声学性能影响的实验研究结果。本文的气动声学部分研究了锯齿形前缘对高自由度湍流干扰宽带噪声的抑制作用。当无量纲频率f ′ < 1时，声压级降低量（ΔSPL）与无量纲频率f ′成线性关系，ΔSPL仅与锯齿振幅、锯齿波长和自由振动速度有关。具有大锯齿幅度的前缘被发现在降低宽带噪声方面非常有效，其中可以实现高达ΔSPL <$8 dB。选择具有较小锯齿波长的前缘通常更有利，尽管最有效的配置实际上结合了最大锯齿振幅和最大锯齿波长。有趣的是，对于弯曲锯齿，发现最优化的配置（具有小锯齿波长、大锯齿振幅、小倾斜角和大曲率半径）在相同频率下宽带噪声进一步降低5 dB，优于其直锯齿对应物。关于研究的空气动力学部分，为了有效地抑制边界层失速而不引起低自由度湍流强度的严重阻力损失，最有效的前缘锯齿应该具有大的锯齿波长和小的锯齿振幅。因此，对于低噪声翼型工作得很好的锯齿几何形状通常在空气动力学性能方面较差，反之亦然。仍能利用航空声学和空气动力学的良好性能的锯齿几何形状的最佳折衷应该具有最大的锯齿幅度和最大的锯齿波长。本文表明，当适当优化时，附加型前缘锯齿在降低干扰宽带噪声和抑制大迎角边界层分离方面都是非常有效的。
This paper presents the results of an experimental study into the effect of add-on type leading edge serrations on the aeroacoustic and aerodynamic performances of a symmetrical NACA0008 aerofoil. The aeroacoustic part of this paper studies the reduction of interaction broadband noise in the presence of elevated freestream turbulence by employing serrated leading edges. For non-dimensional frequenciesf′ < 1, the resulting sound pressure level reduction (ΔSPL) was found to be a linear function off′ and the ΔSPL depends only on the serration amplitude, serration wavelength and freestream velocity. Leading edge with a large serration amplitude was found to be very effective in the reduction of broadband noise where up to ΔSPL ≈ 8 dB is achievable. It is generally more beneficial to choose a leading edge with a smaller serration wavelength, although the most effective configuration actually combines the largest serration amplitude and the largest serration wavelength. Interestingly, for a curved-serration, the most optimised configuration (with small serration wavelength, large serration amplitude, small inclination angle and large curvature radius) was found to outperform its straight-serration counterpart by a further 5 dB reduction of broadband noise at the same frequency. Concerning the aerodynamic part of the study, to effectively suppress boundary layer stall without incurring severe drag penalties for low freestream turbulence intensity, the most effective leading edge serration should possess a large serration wavelength and small serration amplitude. Hence, the serration geometry that works very well for a low noise aerofoil is usually inferior in the aerodynamic performance, and vice versa. The best compromise for the serration geometry that can still harness good performances in both the aeroacoustic and aerodynamic should possess the largest serration amplitude and the largest serration wavelength. This paper demonstrates that, when optimised properly, the add-on type leading edge serration can be very effective in both the reduction of the interaction broadband noise, and the suppression of the boundary layer separation at high angle of attack.