平直槽道流中细长截面柱体涡激振动特性研究

Vortex-induced vibration (VIV) which exists extensively in nature and engineering, is a hot issue in fluid mechanics constantly. This project is to research the dynamic behaviors, as well as the response mechanisms, of a rectangular or elliptical cylindrical oscillator in a novel VIV model system, named the Poiseuille flow-induced vibrations (PFIV) by numerical simulation, experimental investigation, in combination with the theoretical analysis. A significant characteristic of the present PFIV model system is that the cylinder oscillation is excited by the interaction between shedding vortices and channel wall confinement, rather than by the interaction of shedding vortices and structural elasticity for the classic VIV of an elastic structure. The main purpose of this project is to explore and clarify: (1) The characteristics of cylinder motions and vortex shedding modes for PFIV in laminar, transition and turbulent regimes and the mechanisms for the excitations and transitions of response modes in different flow regimes. (2) The mechanism for the phenomenon of critical mass ratio and the theoretical prediction model for critical mass ratio. (3) The intrinsic connections of the inducement mechanisms between PFIV and VIV of an elastic structure. .The present project will be helpful to a comprehensive understanding of the internal mechanism of the present PFIV model system, as well as the intrinsic nature of VIV. The obtention of large-amplitude oscillator with high mass ratio and the production of PFIV in laboratory, will provide new ideas and scientific basis in designing a fluid mixer or a heat transmitter based on PFIV.

涡激振动（VIV）广泛存在于自然界与工程应用，历来是流体力学的热点问题之一。本项目拟采用数值模拟、实验观测并结合理论分析研究长方柱与椭圆柱等具有细长截面的柱状振子在一种新型VIV系统：泊肃叶流致振动（PFIV）中的动力学行为及其响应机理。相对于弹性体VIV，PFIV的主要特征是柱体振动由尾流脱落涡与槽道壁面限制，而非与结构固有弹性，相互作用所激发。研究旨在探索与阐明：（1）层流区、过渡区和湍流区PFIV中柱体运动与涡脱落模态特性及各流动区域响应模态形成与转捩机制；（2）临界质量比现象发生机理及其理论预报模型；（3）PFIV与弹性体VIV诱发机制的内在关联。.项目的实施不仅能够揭示PFIV深层次发生机理，而且有助于深入认识VIV本质，具有重要的理论意义。同时，大振幅高质量比振子的获得和模型系统的实验室实现，为设计依据PFIV机制的高效混合器和换热器提供新的思路与科学依据。

本项目通过数值模拟、实验观测并结合理论分析研究了PFIV以及若干相关问题，取得如下进展：（1）长方柱与椭圆柱PFIV动力学行为丰富并在不同雷诺数、阻塞率、边/轴长比与质量比条件下分别表现为周期、拟周期、二次频等多种不同特性的柱体运动及尾流模态。长方柱较椭圆柱响应特性更为复杂，同时椭圆柱较长方柱振动通常更为剧烈。柱体运动存在临界质量比现象，并对于高阻塞率与低阻塞率情形，分别显示一阶与二阶临界质量比现象。（2）并列双长方柱与椭圆柱PFIV中双柱往往作同步运动。随着边长比增大，双长方柱呈同步反相-同相-反相振动模态二级相变。当雷诺数较小，阻塞率与轴长比较大时，双椭圆柱表现为同步同相振动模态；随着雷诺数增大，阻塞率与轴长比减小，则逐步转变为同步反相振动模态。在两种同步模态之间存在一个双稳过渡模态。（3）根据稳定平衡位置附近受力分布，引入等效弹性系数等概念并依此建立PFIV理论模型，进而阐明响应模态发生机理并揭示PFIV与VIV二者之间内在关联。（4）对于小边/轴长比情形，长方柱与椭圆柱PFIV中均可激发高质量比大振幅振动，为后续研发依据PFIV机制的混溶器、换热器和涡街流量计提供新的思路与科学依据。