Modal analysis of the laminar boundary layer instability and tonal noise of an airfoil at Reynolds number 150,000
Modal analysis of the laminar boundary layer instability and tonal noise of an airfoil at Reynolds number 150,000
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DOI：
10.1177/1475472x18812798
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发表时间：
2018-12
影响因子：
1
通讯作者：
M. Sanjosé;A. Towne;Prateek Jaiswal;S. Moreau;S. Lele;Adrien Mann
中科院分区：
文献类型：
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作者：
M. Sanjosé;A. Towne;Prateek Jaiswal;S. Moreau;S. Lele;Adrien Mann
首次在消声风洞中采用格子Boltzmann方法对5 °攻角、高雷诺数1.5 × 105条件下的可控扩散翼型绕流场进行了直接数值模拟。模拟与壁面压力、尾流统计和远场声的实验测量相比毫不逊色。模拟明显捕捉实验观察到的高振幅的声学音调上升以上的宽带驼峰。这两个噪声分量都与在65-70%的弦附近形成的再循环气泡的呼吸有关，并且与分离的剪切层中的开尔文-亥姆霍兹不稳定性有关，所述剪切层产生分裂成湍流涡流的滚柱，所述湍流涡流在后缘处的衍射产生强偶极声场。结合一些流动可视化的壁压信号的小波分析表明，流量统计主要是由间歇性的，大的和激烈的爆裂辊引起的激烈的事件。这些事件的几个模态分析上的壁压波动和跨度平均流场，以分析边界层的不稳定性，触发典型的尖锐的音调超过宽带驼峰翼型噪声。吸力面Kelvin-Helmholtz不稳定性被观察到与压力面涡脱落相耦合，压力面涡脱落由突然过渡到湍流和钝后缘引起。
A direct numerical simulation of the flow field around a controlled-diffusion airfoil within an anechoic wind-tunnel at 5 ° incidence and a high Reynolds number of 1.5 × 10 5 is performed for the first time using a lattice Boltzmann method. The simulation compares favorably with experimental measurements of wall-pressure, wake statistics, and far-field sound. The simulation noticeably captures experimentally observed high-amplitude acoustic tones that rise above a broadband hump. Both noise components are related to a breathing of a recirculation bubble formed around 65–70% of the chord, and to Kelvin-Helmholtz instabilities in the separated shear layer that yield rollers that break down into turbulent vortices whose diffraction at the trailing edge produces a strong dipole acoustic field. A wavelet analysis of the wall-pressure signals combined with some flow visualization has shown that the flow statistics are dominated by intense events caused by intermittent, large and intense bursting rollers. Several modal analyses of these events are performed on both the wall-pressure fluctuations and the span averaged flow field in order to analyse the boundary layer instability which triggers the typical sharp tones over a broadband hump in airfoil noise. A suction side Kelvin-Helmholtz instability is observed to be coupled with a pressure side vortex shedding induced by the sudden transition to turbulence and the blunt trailing edge.