平面剪切来流作用下串列布置三圆柱流致运动特性研究

基于四步半隐式特征线分裂算子有限元方法,对Re=100时,剪切来流作用下串列三圆柱体双自由度流致振动问题进行了数值计算. 首先,与现有文献结果进行对比验证该方法的正确性. 然后,着重分析剪切率、固有频率比和折减速度三个关键参数对串列三圆柱体结构流致动力响应及流场特性的影响. 数值计算结果表明:剪切率、固有频率比与折减速度对结构振幅和运动轨迹的影响较大. 随剪切率的增大,上游圆柱最大振幅的变化与单圆柱工况类似. 中下游圆柱最大振幅会增大且会出现双向共振现象,同时,发生共振响应区域会扩大. 随固有频率比的增大,上游圆柱顺流向锁定区间范围会减小,而中下游圆柱双向锁定区间会扩大. 另一方面,均匀来流作用下,结构运动轨迹以"8"字形和不规则形状为主. 随剪切率的增大,锁定区间内运动轨迹会由"8"字形转变为"雨滴"形. 在大剪切率与高固有频率比工况下,中游圆柱体结构运动轨迹会出现"双雨滴"形状. 最后,通过对流场特性的分析,揭示了剪切来流作用下串列三圆柱结构流致运动响应的内在机理. 

STUDY OF FLOW-INDUCED MOTION CHARACTERISTICS OF THREE TANDEM CIRCULAR CYLINDERS IN PLANAR SHEAR FLOW1)

Flow-induced motions of three elastically mounted circular cylinders subjected to the planar shear flow in tandem arrangement at $Re =100$ were numerically investigated by using semi-implicit characteristics-based split (CBS) finite element algorithm. Firstly, the results are compared with the existing data in the literature to verify the accurateness of the method. Then, the influence of some key parameters, such as shear ratio ($k$), natural frequency ratio ($r$) and reduced velocity ($U_{\rm r}$) on the characteristics of flow-induced dynamic responses and flow field of three circular cylinders with tandem arrangement was analyzed. The numerical results show that the shear ratio, natural frequency ratio and reduced velocity play an important role in the amplitude and trajectory of motion. The change of maximum amplitude of the upstream cylinder is similar to that of an isolated cylinder case with the increasing of $k$. The maximum amplitudes of the midstream and downstream cylinders increase, and the dual resonance is observed. Meanwhile, the increasing of $k$ causes the extension of the resonance region. With the increasing of $r$, the lock-in region of the upstream cylinder reduces in the in-line direction. However, for the midstream and downstream ones, the dual-lock-in region broadens. On the other hand, the prominent $X-Y$ trajectories of three circular cylinder resemble figure-eight shape and irregular one in the uniform flow. With the change of $k$, the motion orbit transforms from figure-eight to the raindrop shape in the lock-in region. In the larger shear ratio and higher natural frequency ratio case, the dual-raindrop is observed in the $X-Y$ vibrating trajectory of the midstream cylinder. Finally, the flow-induced motion mechanism of three tandem circular cylinders exposed to planar shear flow is revealed according to the analysis of the characteristic of the flow field.