An extensive experimental investigation was undertaken to control the flow and noise characteristics influenced by vortex shedding from a circular cylinder by implementing air blowing at the base of the cylinder. The study synchronised near-field pressure and far-field noise measurements with the wake velocity field to understand the noise reduction mechanism of base blowing. Surface pressure fluctuations were measured using pressure taps distributed around the cylinder's circumference through a remote-sensing method, while velocity measurements were obtained using planar particle image velocimetry at the midspan to examine the flow dynamics. The study unveiled the crucial role of near-field pressure, particularly induced at the shoulders of the cylinder, in generating far-field noise. The rapid vertical flow movement, arising from the interaction between shear layers, was identified as a mechanism responsible for inducing surface pressure fluctuations. This phenomenon occurred as high-momentum fluid moved from the free stream into the interior of the vortex-formation region. By applying base blowing, a remarkable reduction in both near-field pressure and far-field noise was achieved at the fundamental vortex-shedding frequency, with reductions of approximately 20 and 25 dB, respectively, compared with the baseline. Additionally, base blowing caused the shear layers to roll up farther downstream than in the baseline by decreasing the entrainment of fluid-bearing opposite vorticity by the shear layer upstream of the growing vortex. Consequently, there was a substantial decrease in turbulent kinetic energy and Reynolds stress near the cylinder, resulting in slower vertical flow movement and weaker near-field pressure.

中文翻译：

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通过主动底吹控制气缸流量和噪音

进行了广泛的实验研究，通过在圆柱体底部吹气来控制受圆柱体涡流脱落影响的流量和噪声特性。该研究将近场压力和远场噪声测量与尾流速度场同步，以了解底部吹气的降噪机制。通过遥感方法使用分布在圆柱体圆周上的测压孔测量表面压力波动，同时使用中跨处的平面粒子图像测速仪获得速度测量值以检查流动动力学。该研究揭示了近场压力（尤其是在圆柱体肩部产生的压力）在产生远场噪声方面的关键作用。由剪切层之间的相互作用引起的快速垂直流动被认为是引起表面压力波动的机制。当高动量流体从自由流移动到涡流形成区域的内部时，就会发生这种现象。通过应用基础吹气，在基本涡旋脱落频率处实现了近场压力和远场噪声的显着降低，与基线相比分别降低了约 20 和 25 dB。此外，底部吹风通过减少不断增长的涡流上游的剪切层对流体轴承相反涡度的夹带，导致剪切层在下游比基线滚动得更远。因此，圆柱体附近的湍流动能和雷诺应力显着降低，导致垂直流运动减慢和近场压力减弱。