Energy exchanges in the flow past a cylinder with a leeward control rod
Energy exchanges in the flow past a cylinder with a leeward control rod
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DOI：
10.1017/jfm.2022.297
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发表时间：
2022-05
影响因子：
3.7
通讯作者：
Neelakash Biswas;M. Cicolin;O. Buxton
中科院分区：
文献类型：
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作者：
Neelakash Biswas;M. Cicolin;O. Buxton
摘要利用雷诺数为20×10^3的粒子图像测速数据，研究了有背风控制棒的圆柱尾迹中相干结构与平均流动之间的能量交换。控制棒的脱落依赖于迎面而来的剪切层，因此主缸和控制棒尾迹的下游相互作用强烈地依赖于控制棒的安装角。在这项工作中，我们研究了在不同的圆柱体和控制棒的脱落模式之间的相互作用。除了控制棒、主缸及其谐波的脱落频率外，流场中还出现了具有明显特征频率的新的二次相干运动。应用多尺度三重分解方法提取与每个频率相关的相干模式，并利用动能平衡方程研究了模式的动力学行为。控制棒和主缸的一次脱落模式以及主缸脱落模式的谐波主要由此时的平均流量提供能量，而二次模式几乎完全由一次模式提供能量，这与Baj&Buxton(Phys.流体修订版，第2卷，第11期，2017年，114607)，用于不同的多尺度流动配置。在两个不同的研究中观察到的形成二次相干模的能量交换过程的显著相似性，暗示了在多尺度流动中这些二次结构的形成过程可能具有普遍性。
Abstract We study the energy exchanges between coherent structures and the mean flow in the wake of a cylinder in the presence of a leeward control rod using particle image velocimetry data at Reynolds number ($Re$) $20\times 10^3$. The shedding of the control rod depends on the oncoming shear layer and hence the downstream interaction of the main cylinder's and control rod's wake strongly depends on the control rod's setting angle ($\theta$). In this work we study this interaction between the shedding modes from the cylinder and control rod at different $\theta$. New secondary coherent motions with distinct characteristic frequencies appear in the flow field aside from the frequencies associated with the sheddings of the control rod, the main cylinder and its harmonics. A multiscale triple decomposition method is applied to extract the coherent modes associated with each of these frequencies, and the dynamics of the modes are studied using kinetic energy budget equations. The primary shedding modes of the control rod and main cylinder, as well as the harmonics of the main cylinder's shedding modes, are found to be primarily energised by the mean flow at this $Re$, while the secondary modes are almost entirely energised by the primary modes, similar to the findings of Baj & Buxton (Phys. Rev. Fluids, vol. 2, issue 11, 2017, 114607) for a different multiscale flow configuration. The remarkable similarity in the energy exchange process forming the secondary coherent modes, observed in two different studies, hints at a possible universality in the formation process of these secondary structures in a multiscale flow.