低雷诺数下串列布置双圆柱涡激振动特性研究

STUDY ON THE VORTEX-INDUCED VIBRATION CHARACTERISTICS OF TWO TANDEM CYLINDERS AT LOW REYNOLDS NUMBER

基于四步半隐式特征线分裂算子有限元方法,对串列布置双圆柱双自由度涡激振动问题进行了数值模拟计算,并分析了间距比、剪切率、频率比以及折减速度4个参数对圆柱结构动力响应的影响.研究发现:不同固有频率比与剪切率对下游圆柱振动幅值影响较大,然而对上游圆柱振动幅值影响较小.上游圆柱在两个自由度方向达到最大值的折减速度不同,然而下游圆柱基本同步.上游圆柱共振区的范围明显宽于下游圆柱,同时上游圆柱较下游圆柱会更早进入与退出共振区间.另一方面,双圆柱主要在锁定区间完成相位的转变,随频率比增大能量从流体传递到柱体的速度会减慢,导致圆柱体结构完成从同相到反相的转变速度会减慢.剪切来流工况下,当间距比大于3.5时,升力与位移相位差会出现"平台期".当间距比超过临界值时,随着折减速度的增大,流体力功率谱密度曲线出现的杂频会增多,导致出现能量"反哺"现象.最后,在均匀来流工况下,升阻力功率谱密度曲线中主频率值呈两倍关系,然而随着剪切率的增加,流体力功率谱密度曲线会基本重合.

Based on the four-step semi-implicit characteristic line splitting operator finite element method, the vortexinduced vibration problem of two-degree-of-freedom tandem arrangement of double cylinders is numerically simulated,and the spacing ratio, shear ratio, natural frequency ratio and reduced velocity are analyzed. The influence of four parameters on the dynamic response of cylindrical structure.The study found:natural frequency ratio and shear ratio have a greater impact on the vibration amplitude of upstream cylinder. However, the impact of the natural frequency ratio and shear ratio on the downstream cylinder is small.The upstream cylinder reaches the maximum reduction speed in the two degrees of freedom direction is different, but the downstream cylinder is basically synchronized. The resonance area of the upstream cylinder is significantly wider than that of the downstream cylinder. Meanwhile, the time of upstream cylinder enter and exit the resonance area is earlier than that of the downstream cylinder. On the other hand, the two cylinders mainly complete the phase transition in the in-lock region. With the increase of the frequency ratio, the rate of the energy transfer from the fluid to the cylinder slow down, resulting in the slower rate of the cylinder complete the transition of in-phase to anti-phase. In the shear flow case, the phase difference between lift and displacement will appear “platform period” at the space ratio is more than 3.5. When the spacing ratio further increases beyond the critical value, with the increase of the reduced velocity, the more clutter frequency appears in the fluid force power spectral density curve, which leads to the phenomenon of energy “feedback”. Finally, in the uniform flow case,the main frequency value in the lift-drag power spectral density curve is twice the relationship, but as the shear rate increases, the fluid force power spectral density curve will basically coincide.