Bourguet Rémi, Triantafyllou Michael S
Institut de Mécanique des Fluides de Toulouse, Université de Toulouse and CNRS, Toulouse, France
Massachusetts Institute of Technology, Cambridge, MA, USA.
Philos Trans A Math Phys Eng Sci. 2015 Jan 28;373(2033). doi: 10.1098/rsta.2014.0108.
The free vibrations of a flexible circular cylinder inclined at 80° within a uniform current are investigated by means of direct numerical simulation, at Reynolds number 500 based on the body diameter and inflow velocity. In spite of the large inclination angle, the cylinder exhibits regular in-line and cross-flow vibrations excited by the flow through the lock-in mechanism, i.e. synchronization of body motion and vortex formation. A profound reconfiguration of the wake is observed compared with the stationary body case. The vortex-induced vibrations are found to occur under parallel, but also oblique vortex shedding where the spanwise wavenumbers of the wake and structural response coincide. The shedding angle and frequency increase with the spanwise wavenumber. The cylinder vibrations and fluid forces present a persistent spanwise asymmetry which relates to the asymmetry of the local current relative to the body axis, owing to its in-line bending. In particular, the asymmetrical trend of flow-body energy transfer results in a monotonic orientation of the structural waves. Clockwise and counter-clockwise figure eight orbits of the body alternate along the span, but the latter are found to be more favourable to structure excitation. Additional simulations at normal incidence highlight a dramatic deviation from the independence principle, which states that the system behaviour is essentially driven by the normal component of the inflow velocity.
通过直接数值模拟研究了在均匀流中倾斜80°的柔性圆柱体的自由振动，雷诺数基于圆柱直径和流入速度为500。尽管倾斜角度很大，但圆柱体通过锁定机制（即物体运动与涡旋形成的同步）表现出由流动激发的规则的顺流向和横向振动。与静止物体的情况相比，观察到尾流有深刻的重新配置。发现涡激振动在平行但也有斜向涡脱落的情况下发生，此时尾流的展向波数与结构响应一致。脱落角和频率随展向波数增加。圆柱体振动和流体力呈现出持续的展向不对称性，这与局部流相对于物体轴线的不对称性有关，这是由于其顺流向弯曲。特别是，流-体能量传递的不对称趋势导致结构波的单调取向。物体的顺时针和逆时针8字形轨道沿展向交替出现，但发现后者更有利于结构激发。垂直入射时的额外模拟突出了与独立性原理的显著偏差，该原理指出系统行为基本上由流入速度的法向分量驱动。
