Vortex-induced vibrations of a flexible cylinder at subcritical Reynolds number
Vortex-induced vibrations of a flexible cylinder at subcritical Reynolds number
复制标题
亚临界雷诺数下柔性圆柱体的涡激振动
DOI：
10.1017/jfm.2020.676
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发表时间：
2020
影响因子：
3.7
通讯作者：
R. Bourguet
中科院分区：
文献类型：
--
作者：
R. Bourguet
摘要 根据主体直径和流入速度，经过固定刚性圆柱体的流动在超过接近 47 美元的临界雷诺数后变得不稳定。本文以数值方式探讨了柔性圆柱体在亚临界雷诺数 ($Re$)（即 $Re<47$）下可能产生的涡激振动 (VIV)。发现柔性气缸 VIV 的发生率低至 $Re\大约 20$，如之前针对弹性安装刚性气缸的报道。对$Re=25$进行了详细分析，分两步：检查从VIV出现到第一结构模态激发的系统行为；然后重点放在更高模式的响应上。在所有情况下，每个方向都会激发单一振动频率。横流和同轴响应表现出截然不同的幅度（峰值振幅为 0.35 美元，直径为 0.01 美元），以及独特的对称性和演变（例如驻波/行波）。一旦圆柱体振动，流动就会不稳定，并且被发现在时间和空间上与身体运动锁定。无论振动涉及何种模式，与横流驻波响应的同步都伴随着细胞尾流模式的形成。身体轨迹沿跨度变化，但可以识别主要轨道。尽管在线响应的振幅较低，但轨道方向和流结构能量转移之间的联系仍然存在，每个方向都有不同的趋势。
Abstract The flow past a fixed rigid cylinder becomes unsteady beyond a critical Reynolds number close to $47$, based on the body diameter and inflow velocity. The present paper explores numerically the vortex-induced vibrations (VIV) that may develop for a flexible cylinder at subcritical Reynolds number ($Re$), i.e. for $Re<47$. Flexible-cylinder VIV are found to occur down to $Re\approx 20$, as previously reported for elastically mounted rigid cylinders. A detailed analysis is carried out for $Re=25$, in two steps: the system behaviour is examined from the emergence of VIV to the excitation of the first structural modes; and then focus is placed on higher-mode responses. In all cases, a single vibration frequency is excited in each direction. The cross-flow and in-line responses exhibit contrasting magnitudes (peak amplitudes of $0.35$ versus $0.01$ diameters), as well as distinct symmetry properties and evolutions (e.g. standing/travelling waves). The flow, unsteady once the cylinder vibrates, is found to be temporally and spatially locked with body motion. The synchronization with the cross-flow standing-wave responses is accompanied by the formation of cellular wake patterns, regardless of the modes involved in the vibrations. Body trajectory varies along the span, but dominant orbits can be identified. Despite the low amplitudes of the in-line responses, connections are uncovered between orbit orientation and flow–structure energy transfer, with different trends in each direction.