两相混输管道流固耦合振动问题的数值模拟研究

For simulating fluid-structure interactions (FSI) in the pipe conveying two-phase fluid, we improve the two-phase FSI procedure, which is developed with a spectral/hp element method. In the fluid solver, we simulate the coupled Navier-Stokes and Cahn–Hilliard equations for two-phase flows with the phase field approach. For the structure solver, we adopt the three-dimensional beam model to simulate the dynamics of the pipe. A Galerkin method is used in Lagrangian coordinates to solve it. Based on the ALE framework, we finish the coupling between fluid solver and structure solver, and solve the moving mesh problem due to the deformation of the structure. Then we systematically study the characteristics of two-phase flow and the mechanism of two-phase flow induced vibration for a horizontal/inclined/curve pipe. We investigate the two-phase flow instability mechanism and the interaction between two-phase flow pattern and the flutter instability behavior of the pipe. The current project has very important academic value in the area of two-phase FSI algorithm and mechanism study, and it also provides great technical support for the engineering problems related to the induced vibration of pipe conveying two-phase flow.

针对两相混输管道的流固耦合振动问题，首先改进基于高精度谱元算法的两相流-流固耦合计算程序：流体求解器采用相场方法，求解Navier-Stokes和Cahn-Hilliard方程模拟管内两相流的流动。固体求解器则使用三维梁模型模拟管道的振动，并采用拉格朗日坐标系下的伽辽金法进行离散求解。基于任意拉格朗日法（ALE），实现流体和变形体之间的耦合计算，并解决管道变形产生的动网格问题。 然后系统地研究倾斜/弯曲管内两相流动机理、流型变化、管道耦合振动特性，详细地分析两相流动的不稳定特性以及管道振动响应和管内流型变化之间的互相作用。本项目的研究不仅对两相流-流固耦合的算法和物理机理的研究体系具有重要的学术意义，而且可为两相混输管道耦合振动导致的管道损坏等工程问题提供技术支撑。

管道系统越来越广泛地应用于许多领域，如城市供水的长距离管线、大规模集中供暖系统、大型油田的长距离输油管线、核电站中的水循环系统等。管道系统的耦合振动轻则降低系统的可靠性，导致管道渗漏；重则致使系统的损坏和管道的爆裂，并酿成重大事故。本项目首先改进两相流-流固耦合计算程序，开发了适合高雷诺流动的Entropy Viscosity method 以及重力条件下的管道自由端、弹性支撑等边界条件，实现对倾斜、竖直，弯曲等各种两相混输管道的流固耦合振动问题的模拟研究。然后系统地研究各相流动参数、固体参数对管内两相流的不稳定特性以及两相流型变化和管道振动响应之间的互相作用的影响，分析了管道段塞流的形成机制并通过DMD分析得出Rolling Wave模态是导致倾斜管道振动的原因。本项目的研究不仅对两相流-流固耦合的算法和物理机理的研究体系具有重要的学术意义，而且可为两相混输管道耦合振动导致的管道损坏等工程问题提供技术支撑。本项目执行期间，共发表SCI论文8篇，会议论文4篇，参加国内外会议6次，联合培养博士研究生5名，已毕业2名。