Reduction of Emitted Sound by Application of Porous Trailing Edges
Reduction of Emitted Sound by Application of Porous Trailing Edges
复制标题
通过应用多孔后缘减少发出的声音
DOI：
--
复制
发表时间：
2013
期刊：
影响因子：
--
通讯作者：
J. Dierke
中科院分区：
文献类型：
--
作者：
B. Fassmann;J. Delfs;R. Ewert;J. Dierke
对NACA0012翼型后部应用多孔材料降低后缘噪声进行了数值研究。使用了一种简单的各向异性孔隙度，即窄的流向狭缝。它们从后缘向上游延伸11：25%的弦长。缝隙从翼型的上侧到下侧完全渗透到后缘。提出了后缘声减少的三种基本机制：缝隙引起的湍流产生的变化、声吸收和后缘发声过程的变化。
利用计算流体力学(CFD)和计算气动声学(CAA)对这些机理进行了系统的分析。CFD计算结果表明，窄缝对湍流的产生没有明显影响。模拟了两种不同类型的声源，并将其应用于两种不同的声源，即多孔尾缘和固体参考构型。一方面，利用在尾缘产生熟悉的尾缘声指向性的恒定振偶极子来研究声学吸收。另一方面，一个单一的平流涡被初始化，以检查湍流与翼型之间的相互作用，涉及到声音的产生。
目前的计算结果与以前的风洞试验结果相同，声学效益范围为6分贝。研究结果表明，改进后的发声过程对发声效果的影响最大，而纯吸声仅在较小的传播角范围内起重要作用。
The reduction of trailing edge sound by application of porous material at the rear part of a NACA0012 airfoil is investigated numerically. A simple, anisotropic porosity is used, namely narrow streamwise slits. They extend by 11:25% of the chord length upstream from the trailing edge. The slits completely permeate the trailing edge from the upper side of the airfoil to the lower side. Three colluding fundamental mechanisms are suggested to be responsible for the reduction of trailing edge sound: The change of turbulence production due to the slits, the acoustic absorption, and the change of the sound generating process at the trailing edge.
These mechanisms are analysed systematically by means of Computational Fluid Dynamics (CFD) and Computational Aero-Acoustics (CAA). The CFD results show no significant impact of the narrow slits on the turbulence production. Two different kinds of acoustic sources are modelled and applied to both, a porous trailing edge and a solid reference configuration. On the one hand, the acoustic absorption is investigated by use of a constantly vibrating dipole at the trailing edge which is generating the familiar directivity of trailing edge sound. On the other hand, a single advecting vortex is initialised to examine the interaction between the turbulence and the airfoil concerning the generation of sound.
The current computational results show the same range of acoustic benefit of 6 dB like former wind tunnel tests. The findings illustrate that the modified sound generating process has the major influence, while pure absorption is important only in a narrow range of propagation angles.