低雷诺数中等间距串列双方柱涡激振动的数值模拟

Numerical simulation on vortex-induced vibration of two tandem square cylinders with medium spacing at a low Reynolds number

摘要:

为研究典型间距比串列双方柱的涡激振动特性及其耦合机制,对雷诺数为150、柱心间距比分别为2.0和4.0的串列双方柱涡激振动进行了数值模拟,探讨了方柱振动响应随来流折减速度的变化规律,以及周围流场的流态与其演变过程,重点分析了下游方柱的能量输入机制.两方柱在不同柱心间距比下均以横流向振动为主,柱心间距比为2.0时,均在双涡脱流态内发生“弱锁定”（即方柱在振动锁定区的振动频率锁定值远小于1.0）,其横流向最大振幅皆出现在振动锁定区内且上游方柱振幅较大；在振动锁定区内,上游方柱平均阻力系数的激增导致平均柱心间距急剧减小,扰乱了下游方柱的气动升力对振动的能量输入,导致其尾流中的旋涡极不稳定.柱心间距比为4.0时,仅下游方柱在剪切层再附流态内发生“锁定”,两方柱的横流向最大振幅均出现在振动锁定区外,但上游方柱振幅远小于下游方柱,这是由于两方柱脱落的旋涡相互融合,使得气动升力对下游方柱的能量输入增强,横流向振幅和旋涡的横流向间距随之增大,造成下游方柱的尾流模态为双涡脱流态内的平行涡街模态.此外,下游方柱的横流向振幅在剪切层再附流态内也会出现较明显的极值,其对应的尾流模态均为剪切层再附流态内的平行涡街模态.

Abstract:

To investigate the vortex-induced vibration characteristics and coupling mechanisms of two tandem square cylinders with typical spacing ratio, vortex-induced vibration of two tandem square cylinders was numerically simulated at Reynolds number Re=150 with two spacing ratios of 2.0 and 4.0, and variations of the vibration responses with reduced velocity were studied. The flow pattern and the evolution of the flow field around the cylinders were discussed, and the energy input mechanism for the downstream cylinder was emphatically analyzed. The vibrations of the two cylinders were mainly in the transverse direction for the two spacing ratios. When the spacing ratio was 2.0, the “soft-lock-in” phenomenon occurred in the co-shedding regime for both cylinders (with the lock-in frequency much less than 1.0 in the vibration lock-in region). The maximum transverse amplitudes of the two cylinders both appeared in the vibration lock-in region, and the maximum amplitude of the upstream cylinder was larger. In the vibration lock-in region, due to the abrupt increase of the mean drag force of the upstream cylinder, the mean distance between the two cylinders severely decreased, which disturbed the energy input of the lift force to the vibration of the downstream cylinder. Thus, the vortex in the wake region of the downstream cylinder became unstable. When the spacing ratio was 4.0, the “lock-in” phenomenon was only observed for the downstream cylinder in the reattachment regime. The maximum transverse amplitudes of the two cylinders appeared outside the vibration lock-in region, and the maximum amplitude of the upstream cylinder was much smaller than that of the downstream cylinder. Caused by the mixing of the vortex generated by the two cylinders, the energy input of the lift force for the downstream cylinder was enhanced, enlarging its transverse amplitude. The transverse distance between the two cylinders increased accordingly, which resulted in the parallel vortex street mode of the co-shedding regime in the wake region of the downstream cylinder. In addition, the transverse amplitudes of the downstream cylinder had obvious extreme values in the reattachment regime, and the corresponding wake modes were all parallel vortex street mode of the reattachment regime.