Abstract

One known method to reduce vortex shedding from the tip of a blade is the use of end plates or winglets. Although the aerodynamic impact of such end plates has been investigated in the past, no studies exist on the effect of such end plates on the far-field noise. The aeroacoustic noise reduction of three different end-plate geometries is experimentally investigated. The end plates are applied to the free end of a wall-mounted symmetric NACA 0012 airfoil and a cambered NACA 4412 airfoil with an aspect ratio of 2 and natural boundary layer transition. Microphone array measurements are taken in the aeroacoustic open-jet wind tunnel at BTU Cottbus-Senftenberg for chord-based Reynolds numbers between 75,000 and 225,000 and angles of attack from 0\(^\circ\) to 30\(^\circ\). The obtained acoustic spectra show a broad frequency hump for the airfoil base configurations at higher angles of attack that is attributed to tip noise. Hot-wire measurements taken for one configuration show that the application of an end plate diffuses the vorticity at the tip. The aeroacoustic noise contribution of the tip can be reduced when the endplates are applied. This reduction is most effective for higher angles of attack, when the tip vortex is the dominant sound source.

Graphic abstract

中文翻译：

---

通过在壁挂式有限型机翼上安装端板来降低航空声噪声

摘要

减少涡旋从叶片尖端脱落的一种已知方法是使用端板或小翼。尽管过去已经研究了这种端板的空气动力学影响，但是还没有关于这种端板对远场噪声的影响的研究。实验研究了三种不同端板几何形状的空气声降噪。将端板施加到壁装对称NACA 0012机翼和弧形NACA 4412机翼的自由端，其宽高比为2，并且具有自然边界层过渡。麦克风阵列的测量是在BTU Cottbus-Senftenberg的空气声学开放式风洞中进行的，基于弦的雷诺数在75,000到225,000之间，迎角从0 \（^ \ circ \）到30 \（^ \ circ \）。所获得的声谱在较高的迎角处显示出翼型基座配置的宽广的频率峰，这归因于叶尖噪声。对一种配置进行的热线测量表明，端板的应用使尖端处的涡流扩散。使用端板时，可以降低尖端的空气声噪声贡献。当尖端涡旋是主要的声源时，这种减小对于较大的迎角是最有效的。

图形摘要