On the role of turbulence distortion on leading-edge noise reduction by means of porosity
On the role of turbulence distortion on leading-edge noise reduction by means of porosity
复制标题
DOI：
10.1016/j.jsv.2020.115561
复制
发表时间：
2020-10
影响因子：
4.7
通讯作者：
R. Zamponi;S. Satcunanathan;S. Moreau;D. Ragni;M. Meinke;W. Schröder;C. Schram
中科院分区：
文献类型：
--
作者：
R. Zamponi;S. Satcunanathan;S. Moreau;D. Ragni;M. Meinke;W. Schröder;C. Schram
一种可能的策略，用于减少由湍流与机翼轮廓相互作用产生的航空声学噪声，也称为前缘噪声，通过在翼型结构中实施多孔介质来表示。然而，这种噪声缓解技术所涉及的物理机制仍然不清楚。本工作的目的是阐明这些现象，特别是如何孔隙度影响传入的湍流特性的表面附近。装有三聚氰胺泡沫的多孔NACA-0024型面已与固体基线进行了比较，这两种翼型又受到上游圆杆产生的湍流的影响。沿着翼型的平均壁压分布表明，多孔材料的应用基本上保持了NACA-0024型面形状的完整性。热线风速仪和大涡模拟的结果表明，在这项研究中提出的多孔设计允许阻尼的速度波动，它对上游平均流场的影响有限。具体而言，上洗分量的均方根的速度波动原来是显着衰减，在多孔的情况下，在固体的对比，导致在滞止区的湍流动能的强烈减少。此外，入射湍流速度的功率谱密度之间的比较表明，孔隙率主要对湍流速度功率谱的低频范围的影响。这一证据与声学波束形成测量的结果一致，该结果在类似的频率范围内表现出噪声抑制。在此基础上，结合快速畸变理论的理论输入，对翼型多孔处理引起的共振-相互作用降噪现象进行了解释。
A possible strategy for the reduction of the aeroacoustic noise generated by turbulence interacting with a wing profile, also referred to as leading-edge noise, is represented by the implementation of a porous medium in the structure of the airfoil. However, the physical mechanisms involved in this noise mitigation technique remain unclear. The present work aims at elucidating these phenomena and particularly how the porosity affects the incoming turbulence characteristics in the immediate vicinity of the surface. A porous NACA-0024 profile equipped with melamine foam has been compared with a solid baseline, both airfoils being in turn subjected to the turbulence shed by an upstream circular rod. The mean wall-pressure distribution along the airfoils shows that the implementation of the porous material mostly preserves the integrity of the NACA-0024 profile's shape. Results of hot-wire anemometry and large-eddy simulations indicate that the porous design proposed in this study allows for a damping of the velocity fluctuations and it has a limited influence on the upstream mean flow field. Specifically, the upwash component of the root-mean-square of the velocity fluctuations turns out to be significantly attenuated in the porous case in contrast to the solid one, leading to a strong decrease of the turbulent kinetic energy in the stagnation region. Furthermore, the comparison between the power spectral densities of the incident turbulent velocities demonstrates that the porosity has an effect mainly on the low-frequency range of the turbulent velocity power spectrum. This evidence is in line with the results of the acoustic beamforming measurements, which exhibit a noise abatement in an analogous frequency range. On the basis of these observations, an interpretation of the phenomena occurring in the turbulence-interaction noise reduction due to a porous treatment of the airfoil is finally given with reference to the theoretical inputs of the Rapid Distortion Theory.