并列双圆柱流致振动的不对称振动和对称性迟滞研究

对雷诺数Re = 100 间距比s/D = 2.5 和5.0 的并列双圆柱流致振动进行了数值模拟研究, 其中圆柱质量比m = 2.0, 折合流速U_r 在2.0~10.0 之间, 两圆柱仅能做横流向振动. 研究发现, 当间距比s/D = 2.5 时, 在折合流速4.4 < U_r< 4.8区间内, 两圆柱流致振动响应出现不对称振动现象, 在折合流速4.4 < U_r< 4.8 区间内, 两圆柱流致振动响应出现对称性迟滞现象; 而当间距比s/D = 2.5时, 圆柱流致振动响应与单圆柱涡激振动响应相似, 没有出现不对称振动和对称性迟滞现象. 在不对称振动区间内, 两圆柱的升、阻力参数也出现了不相等的情况. 此外, 当两圆柱不对称振动时, 圆柱间隙流稳定地偏斜向其中的一个圆柱; 相应地, 尾涡也出现了宽窄不等的模式. 窄尾流圆柱的振幅和升、阻力均较宽尾流圆柱的大. 通过对比不对称振动现象发生前后的尾涡模式, 对新现象的产生机制进行了阐述.

NUMERICAL INVESTIGATION ON THE ASYMMETRIC VIBRATION AND SYMMETRY HYSTERESIS OF FLOW-INDUCED VIBRATION OF TWO SIDE-BY-SIDE CYLINDERS

Flow-induced vibration of two side-by-side circular cylinders at Re= 100 is numerically investigated. The cylinders are constrained to oscillate in the cross-flow direction with a center-to-center spacing ratio s/D = 2.5 and 5.0. The mass ratio of the cylinders is 2.0 and the reduced velocity is U_r= 2.0 ～ 10.0. The results show that, for the case with s/D = 2.5, asymmetric vibrations of the two side-by-side cylinders is observed in 4.0 < U_r< 4.8, while the symmetry hysteresis is observed in 4.4 < U_r< 4.8. However, for the case with s/D = 5.0, both two phenomena disappear and the vibration responses of two side-by-side circular cylinders are close to those of an isolated circular cylinder. Moreover, it was found that the lift and drag coefficients of the two cylinders also showed asymmetric features in the asymmetric vibrations region. When the two cylinders oscillate with different amplitudes, the gap flow stably biases to one of the cylinders and thus leads to a wide-narrow near-wake pattern. The cylinder with the narrower near-wake has larger vibration amplitude, drag and lift forces than the other one with the wider near-wake. A detailed explanation on the mechanisms of the asymmetric vibration and symmetry hysteresis is presented from the point of view of near-wake patterns before and after the asymmetric vibration occurs.