被动控制下钝体涡致振动强化机制与驰振产生机理研究

Flow-induced motion(FIM) is widely existing in the nature and engineering applications. The interactions of the structure and flow are often very complex and the FIM is one of the research focuses in the fluid-structure interaction dynamics. Vortex-induced vibration and galloping are the most commonly observed FIM phenomena. However, the nonlinear behaviors of the vortex-induced vibration and galloping are still lack of understanding, especially for the transition from vortex-induced vibration to galloping in the relatively low speed flow. Therefore, this project studies the enhancement of vortex-induced vibration and mechanism of galloping of bluff body with passive control by means of numerical simulation and experimental observation. First, the essential features and wake vortex patterns of various FIM branches are explored very carefully by numerical simulation and flow visualization. Then, effects of surface roughness height, density, coverage, and arrangements on the flow around a bluff body are analyzed. The passive control methods and the physical mechanism of the enhancement of vortex-induced vibration are examined under different conditions. Finally, the transition from vortex-induced vibration to galloping is initiated for cylinder with passive control and the mechanism of galloping is investigated. The highest oscillatory potential of cylinder in the flow field can be explored for the utilization of relatively low speed flow energy. The proposed project has high scientific and academic values in advancing the fluid-structure interaction dynamics theory and control methods of FIM, as well as great significance for promoting the development of the national economy and the utilization technology of renewable energy.

流致振动是自然界和工程领域中普遍存在的一种流固耦合现象，其流固耦合过程非常复杂，涉及许多科学上的难题，一直是国际前沿研究热点之一。涡致振动和驰振是最为常见的两种流致振动现象，目前对于较低折减速度下涡致振动向驰振转变的机理尚不清楚，存在大量的问题亟需进一步深入研究。本项目采用数值模拟和实验观测相结合的方法，研究被动控制下钝体涡致振动强化机制与驰振产生机理，明确钝体各个振动分支的基本特征及其与尾迹旋涡结构的关系，分析粗糙表面对钝体涡致振动的影响，提出涡致振动的控制方法及其强化措施，认知被动控制下强化钝体涡致振动的物理机制，进而在较低折减速度下实现涡致振动向驰振的转变，揭示驰振产生机理，激发流体中物体极限振动潜能，探索利用低速流动能的合理途径。研究结果对于丰富和发展流固耦合动力学理论及流致振动的控制与利用方法具有非常重要的学术价值，同时对推动可再生能源利用技术和国民经济的发展具有重要意义。

在许多与流体有关的机械与工程中，流致振动是一个涉及安全性的重大问题，其流固耦合过程非常复杂，涉及许多科学上的难题。本项目采用数值模拟和实验观测相结合的方法，研究被动控制下钝体涡致振动强化机制与驰振产生机理。主要结论如下：（1）获得了被动控制单圆柱流致振动响应特征及尾流旋涡演变规律，观察到振动响应曲线出现涡致振动初支、上支和驰振三个分支，每个振动周期脱落的旋涡数量随着来流速度上升而增加，尾流旋涡形态随振动分支的切换而变化。（2）钝体截面形状对流致振动产生明显影响，被动控制圆柱和类梯形柱的边界层分离点位于钝体前端，边界层的分离点对钝体受力影响较大，在相同来流条件时，粗糙表面圆柱和类梯形柱的流致振动响应均强于其他形状钝体。（3）钝体尾流区安装分隔板时，当板长大于4.75D（D为钝体特征尺寸）时，分隔板将完全阻断剪切层之间的相互作用，钝体振动被抑制；弹性分隔板可随钝体振动而发生振动形变，采用压电片作为弹性分隔板可有效收集低速流动能。（4）得到了间隙距离对串行排列双钝体流致振动的影响规律，对于间距大于2D的串列双圆柱，上游圆柱振动响应不受下游圆柱的影响；间距大于3D时，下游圆柱驰振区域与其涡致振动上支并没有明显的过渡点；对于串列双方柱，柱体流致振动在间距4D时得到加强，上下游方柱达到最大振幅。（5）钝体产生涡致振动的激励机制是基于旋涡的交替脱落引发的振荡升力；当振动由涡致振动向驰振过渡时，旋涡脱落形态随之改变，振动激励机制也随之变化；驰振发生时，在旋涡形成过程中，分离剪切层被拉伸到几乎垂直于来流方向，使钝体受到的升力急剧增大，造成系统负阻尼引起的升力不稳定性是激励高振幅低频率驰振的主要原因。研究结果对于丰富和发展流固耦合动力学理论及流致振动的控制利用方法具有非常重要的学术价值。