串列双圆柱绕流下游圆柱两自由度涡致振动研究

数值研究了串列双圆柱绕流下游圆柱两自由度涡致振动问题，研究发现：(1) 双自由度的圆柱振幅峰值及出现振峰的频率比都比单自由度的大；(2) 尾流圆柱中的升力远大于均匀来流的，而阻力却相反；(3) 下游圆柱的位移响应对于频率比的变化没有均匀来流中的"敏感"；(4) 尾流中，在频率比1.16和0.87之间，出现了明显的"拍"现象，即圆柱的振幅响应包含不同的频率，而在均匀来流中，并无明显的"拍"现象. 采用ALE方法，计算网格采用H-O非交错网格系统，结合分块耦合方法. N-S方程的对流项和扩散项分别采用三阶迎风紧致格式和四阶中心紧致格式离散. 圆柱振动采用弹簧柱体阻尼器模型，柱体的振动方程采用龙格-库塔法求解. 通过模拟柱体和流体之间的非线性耦合作用，成功地捕捉到了"拍"和"相位开关"等现象.

The numerical study of two-degree-of-freedom vortex-induced vibration of the downstream cylinder in tandem arrangement

A numerical study has been conducted into two-degree-of-freedom vortex-induced vibrations of the downstream elastic circular cylinder in tandem arrangement. The results show that (i) the peak value of the displacement of the cylinder for two-degree-of-freedom is larger than that for one-degree-of-freedom as well as the ratio of the frequency for which this maximum occurs; (ii) the lift of the cylinder in a wake is more larger than that in a uniform flow, but the drag behaves contrary; (iii) the response of the displacement of the downstream cylinder is less of "sensitivity" than that of the cylinder in a uniform flow at various natural frequency of the cylinder; (iv) the "beating", that is the response of the oscillating cylinder involves various frequencies, are clearly showed in a wake at various ratio of the frequency from 1.16 to 0.87 but not in the uniform flow. The ALE method is adopted with an H-O type of non-stagger grid incorporating the DDM (domain decomposition method). The N-S equation's convection term and dissipation term are discretized using the third-order upwind compact scheme and the fourth-order central compact scheme, respectively. The motion of the cylinder is modeled by a spring-damper-mass system and solved using the Runge-Kutta method. By simulating the non-linear interaction of the fluid-structure system, we successfully captured the "beating" and "phase switch" phenomena.