Distributed lock-in drives broadband vortex-induced vibrations of a long flexible cylinder in shear flow
Distributed lock-in drives broadband vortex-induced vibrations of a long flexible cylinder in shear flow
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DOI：
10.1017/jfm.2012.576
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发表时间：
2013-02
影响因子：
3.7
通讯作者：
R. Bourguet;G. Karniadakis;M. Triantafyllou
中科院分区：
文献类型：
--
作者：
R. Bourguet;G. Karniadakis;M. Triantafyllou
摘要处于剪切横流中的细长柔性体可能会发生涡激振动(VIVS)，其涉及的激励频率和结构波数范围很大。采用直接数值模拟的方法，研究了长径比为200的圆柱形张拉梁在沿跨度呈指数变化的剪切流中产生宽带涡激振动的机理。根据最大速度，雷诺数等于330，与前人关于线性剪切流动中窄带振动的工作进行了比较。在尾迹同步或锁定的条件下，流动被发现在许多不同的位置激励结构。宽带响应与锁定条件沿跨度分布的出现有关，而不是局限于高流入速度区的局部锁定区域，报告的是剪切电流中的窄带振动。尽管宽带响应具有瞬时多频率特性，但锁定现象仍然是局部单频事件，因为涡旋的形成通常与给定位置的单一振动频率同步。激发区的展向分布导致行波结构波在两个方向上移动；这与窄带情况形成对比，窄带情况下传播方向倾向于降低流入速度。对宽带VIV在锁定条件下顺流和横流响应之间的锁相机理进行了推广。高波数振动分量的顺流/横流相位差在展宽方向上的漂移与相应结构波的强烈行波特性有关。
Abstract A slender flexible body immersed in sheared cross-flow may exhibit vortex-induced vibrations (VIVs) involving a wide range of excited frequencies and structural wavenumbers. The mechanisms of broadband VIVs of a cylindrical tensioned beam of length-to-diameter aspect ratio 200 placed in shear flow, with an exponentially varying profile along the span, are investigated by means of direct numerical simulation. The Reynolds number is equal to 330 based on the maximum velocity, for comparison with previous work on narrowband vibrations in linear shear flow. The flow is found to excite the structure at a number of different locations under a condition of wake–body synchronization, or lock-in. Broadband responses are associated with a distributed occurrence of the lock-in condition along the span, as opposed to the localized lock-in regions limited to the high inflow velocity zone, reported for narrowband vibrations in sheared current. Despite the instantaneously multi-frequency nature of broadband responses, the lock-in phenomenon remains a locally mono-frequency event, since the vortex formation is generally synchronized with a single vibration frequency at a given location. The spanwise distribution of the excitation zones induces travelling structural waves moving in both directions; this contrasts with the narrowband case where the direction of propagation toward decreasing inflow velocity is preferred. A generalization of the mechanism of phase-locking between the in-line and cross-flow responses is proposed for broadband VIVs under the lock-in condition. A spanwise drift of the in-line/cross-flow phase difference is identified for the high-wavenumber vibration components; this drift is related to the strong travelling wave character of the corresponding structural waves.