Abstract

The flow field on solid and porous airfoils subjected to turbulence shed by an upstream cylindrical rod and the corresponding far-field noise radiations are studied through particle image velocimetry (PIV) and microphone measurements, respectively. Three different Reynolds numbers based on the rod diameter are considered in a range between \({2.7\times 10^4}\) and \({5.4\times 10^4}\), and two porous airfoil models are tested to analyze the influence of the design elements of the permeable treatment. A standard proper orthogonal decomposition (POD) algorithm is employed to band filter the different length scales that characterize the turbulent flow, making it feasible to determine which turbulence scales are affected by porosity. The aeroacoustic results indicate that the porous treatment of the wing profile leads to a noise reduction at low frequencies and a noise regeneration at high frequencies due to surface roughness. The investigation on the flow field shows that the main effect of porosity is to mitigate the turbulent kinetic energy in the stagnation region, attenuating the distortion of turbulence interacting with the airfoil surface. The application of the POD algorithm indicates that this effect acts mainly on the largest scales of turbulence.

Graphic abstract

中文翻译：

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湍流相干结构与多孔翼型相互作用的实验研究

摘要

分别通过粒子图像测速（PIV）和传声器测量研究了固态和多孔翼型上的流场，这些翼型受到上游圆柱杆的湍流和相应的远场噪声辐射的影响。考虑基于杆直径的三个不同的雷诺数，范围在\（{2.7 \ times 10 ^ 4} \）和\（{5.4 \ times 10 ^ 4} \）之间，并测试了两个多孔翼型模型，以分析渗透处理设计元素的影响。采用标准的适当正交分解（POD）算法对表征湍流的不同长度尺度进行带式滤波，从而确定哪些湍流尺度受孔隙度影响是可行的。空气声结果表明，机翼轮廓的多孔处理导致低频降噪，以及由于表面粗糙度而导致高频降噪。对流场的研究表明，孔隙度的主要作用是减轻滞流区域内的湍动能，从而减弱湍流与机翼表面相互作用的畸变。

图形摘要