The fluid-structure interaction mechanisms of a coating composed of flexible flaps immersed in a periodically oscillating channel flow is here studied by means of numerical simulation, employing the Euler-Bernoulli equations to account for the flexibility of the structures. A set of passively actuated flaps have previously been demonstrated to deliver favourable aerodynamic impact when attached to a bluff body undergoing periodic vortex shedding. As such, the present configuration is identified to provide a useful test-bed to better understand this mechanism, thought to be linked to experimentally observed travelling waves. Having previously validated and elucidated the flow mechanism in Paper 1 of this series, we hereby undertake a more detailed analysis of spectra obtained for different natural frequency of structures and different configurations, in order to better characterize the mechanisms involved in the organized motion of the structures. Herein, this wave-like behaviour, observed at the tips of flexible structures via interaction with the fluid flow, is characterized by examining the time history of the filaments motion and the corresponding effects on the fluid flow, in terms of dynamics and frequency of the fluid velocity. Results indicate that the wave motion behaviour is associated with the formation of vortices in the gaps between the flaps, which itself are a function of the structural resistance to the cross flow. In addition, formation of vortices upstream of the leading and downstream of the trailing flap is seen, which interact with the formation of the shear-layer on top of the row. This leads to a phase shift in the wave-type motion along the row that resembles the observation in the cylinder case.

中文翻译：

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PELskin 项目：第二部分——研究振荡流中柔性长丝之间的物理耦合

本文通过数值模拟研究了由浸入周期性振荡通道流中的柔性襟翼组成的涂层的流固耦合机制，使用欧拉-伯努利方程来解释结构的柔韧性。一组被动致动襟翼先前已被证明当连接到经历周期性涡旋脱落的钝体时可提供有利的空气动力学冲击。因此，目前的配置被确定为提供一个有用的试验台来更好地理解这种机制，被认为与实验观察到的行波有关。之前已经验证并阐明了本系列论文 1 中的流动机制，我们在此对结构的不同固有频率和不同配置获得的光谱进行更详细的分析，以更好地表征结构有组织的运动所涉及的机制。在这里，通过与流体流动的相互作用在柔性结构的尖端观察到的这种波浪状行为的特征是检查细丝运动的时间历程和对流体流动的相应影响，在动力学和频率方面流体速度。结果表明，波浪运动行为与襟翼之间间隙中涡流的形成有关，涡流本身是结构对横向流动的阻力的函数。此外，还可以看到在尾翼的前导和下游形成涡流，这与行顶部剪切层的形成相互作用。这导致沿行的波浪型运动的相移，类似于圆柱情况下的观察。