平直槽道内柱体绕流场中流致振动的研究

A novel physical model system, the flow-induced vibrations in flow around cylinders in a plane channel (PFIV), will be researched in this project to investigate the dynamics behaviors and the internal mechanism of such a system. Using the two- and three- dimensional lattice Boltzmann equations, the model systems of one degree-of-freedom (the oscillators are free to move in the transverse direction) and two degree-of-freedom (the oscillators are free to move in the transverse direction and to rotate around their axes) will be numerically simulated, respectively. The motion types of one, two side-by-side and two tandem circular and square cylinders and the corresponding flow structures will be investigated at different physical conditions. For the case of an isolated circular cylinder with one degree-of-freedom, an equivalent elastic coefficient will be introduced to construct a preliminary theory, by which the dynamic mechanism of the PFIV will be described. The dynamics behaviors and the mechanisms of the PFIV will be compared to that of the classic elastically mounted cylinder to explore the intrinsic nature of the flow-induced vibrations (FIV). The present study will be helpful to a comprehensive understanding of the dynamics behaviors and internal mechanism of the present model system, to provide scientific evidence to establish the present model system as a novel type of FIV, and to provide new ideas in designing a fluid mixer or a heat transmitter.

以一种新型的动力学系统：平直槽道内柱体绕流场中流致柱体振动（PFIV）为研究对象，旨在对其动力学行为及其内在机理进行探索。拟采用二维和三维格子Boltzmann方程对单自由度（振子仅作横向运动）与双自由度（振子可同时作横向运动和绕柱体轴线旋转）系统分别加以直接数值模拟。获得按单体、并列和串列双体等方式排列的圆柱形和方柱形振子，在不同物理参数条件下的运动方式以及相应的流场结构。针对单自由度单圆柱PFIV，拟通过引入等效弹性系数概念建立一个初步的理论模型并以此分析其动力学机制。分析PFIV与弹性支撑柱体的形成机理的异同，以深化对流致振动（FIV）内在本质的认识。通过本项目研究可全面认识PFIV的动力学行为及其形成机理，为确立其作为一种新型FIV提供科学依据，而且为设计高效混溶器和换热器提供新的思路。

本项目通过格子Boltzmann方法研究一种新型涡激振动（VIV）系统：Poiseuille流致振动（PFIV）并取得以下进展：（1）研究了圆柱与方柱PFIV在不同雷诺数、阻塞率、质量比及截面长宽比等物理参数下的动力学行为。结果显示柱体振动广泛存在并表现为周期振动、拟周期振动、拍击振动、弛振等多种不同特征的运动模态与双列涡、单列涡、多涡脱落等多种尾流模态。观测到临界质量比、临界阻塞率与临界截面长宽比等临界现象。（2）对于双柱体PFIV，间距比往往起着关键性作用。当间距比较小时，柱体之间由于间隙流而产生强烈的相互干扰。柱体耦合运动发生多次相变并表现为同步同相振动、同步反相振动、竞争振动、翻滚振动等多种模态。（3）引入稳定平衡位置、等效弹性系数等概念并结合柱体受力、频谱与涡脱落模态分析，揭示了各种运动模态的形成与转捩机理并解释了所观测到的临界现象。研究成果阐明了PFIV的内在机理，并通过与弹性体VIV进行对比分析，发现二者之间存在内在关联，从而深化了对VIV本质的认识。（4）在亚临界区圆柱PFIV与低截面长宽比方柱PFIV中，均观测到了高质量比大振幅振动，为研发依据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。