强非线性自由面运动的CFD模型研究

发布时间：2018-03-05 12:22

本文选题：计算流体力学　切入点：自由面运动　出处：《浙江大学》2016年硕士论文　论文类型：学位论文

【摘要】：自由面运动是自然界中的一种常见现象,与人类的生存发展息息相关,在科学研究和工程应用中都有着重要的价值.然而,自由面运动是一种复杂的现象,尤其是强非线性自由面的运动,目前仍然存在很多难题有待解决.近些年来,CFD (Computational Fluid Dynamics,计算流体力学)已经被证明是一种研究自由面运动的有效手段并被广泛应用到相关研究中.本文采用自主发展的CIP-ZJU (Constraint Interpolation Profile Model in Zhejiang Univer-sity)模型来研究强非线性自由面运动,流场求解器方面,本模型采用时间,空间均为三阶的CIP方法保证了对流项的高精度求解；采用中心差分格式进行扩散性的求解；采用超松弛迭代方法求解压力Poisson方程.自由面捕捉方面,本模型包括两种高精度的VOF (Volume of Fluid,流体体积法)和一种质量守恒型的Level Set方法.同时,本文引入了基于密度重构的平衡型CSF (Continuum Surface Force)模型以及针对于欧拉网格下同种液体不同相之间界面追踪的双液相VOF方法.根据建立的模型,开展了强非线性自由面运动问题的数值模拟,包括溃坝问题,液滴冲击自由面,气泡上升,水面结构物附近波浪诱导涡等.在溃坝问题的数值研究中,本文首先根据实验结果得到一个溃坝试验中挡板运动的经验公式并进行验证,并应用于干底床和湿底床溃坝问题溃坝的数值研究,重点分析了挡板运动对于溃坝问题中水舌运动,自由面形态,压力变化等影响；此外还开展了液滴冲击自由面和三维气泡上升的数值模拟,重点观测了其演变过程中表面张力的作用及自由面的运动;在水面结构物附近波浪诱导涡的初步数值研究中,本文对规则波作用下不同宽度,纵深的薄板附近波浪诱导涡进行了数值观测,对于水面结构物附近诱导涡的运动规律有了初步的认识,为未来更深入的研究打下了良好的基础.本文的主要创新点如下：(1)提出了一种双液相VOF方法,实现了欧拉坐标系下同种流体不同相多相流体之间追踪和相互作用研究,并成功将其应用到湿底床溃坝的数值研究中.(2)提出了一种质量守恒型的Level Set方法,有效改进了Level Set方法的质量守恒率.(3)根据实验公式给出了一个溃坝试验中挡板运动的经验公式并将公式应用到数值模型中,改进了溃坝数值模拟的精度.(4)系统地研究了溃坝问题中挡板运动对溃坝水舌传播,自由面演变,后方直墙冲击压力的影响.
[Abstract]:Free surface motion is a common phenomenon in nature, closely related to the survival and development of human beings, and has important value in scientific research and engineering applications. However, free surface motion is a complex phenomenon. Especially the motion of strongly nonlinear free surface, There are still many problems to be solved. In recent years, Computational Fluid Dynamics (CFD) has been proved to be an effective method to study free surface motion and has been widely used in related research. The CIP-ZJU constraint Interpolation Profile Model in Zhejiang Univer-sitymodel is used to study strongly nonlinear free surface motion. In the aspect of flow field solver, the CIP method of time and space is adopted to ensure the accurate solution of the convection term, and the central difference scheme is used to solve the diffusivity. The overrelaxation iterative method is used to solve the pressure Poisson equation. In the aspect of free surface capture, this model includes two kinds of high-precision VOF volume of fluid (fluid volume method) and a mass-conserved Level Set method. In this paper, the equilibrium CSF continuous Surface Force model based on density reconstruction and the two-phase VOF method for the interface tracing between different phases of the same liquid under Eulerian grid are introduced. Numerical simulation of strongly nonlinear free surface motion is carried out, including dam-break problem, droplet impact on free surface, bubble rise, wave induced vorticity near water surface structure, and so on. Based on the experimental results, an empirical formula of baffle motion in dam-break test is obtained and verified in this paper, and it is applied to the numerical study of dam-break in dry bed and wet bed. The effects of baffle motion on the motion of water tongue, free surface and pressure are analyzed, and the numerical simulation of droplet impact on free surface and three dimensional bubble rise is also carried out. The effect of surface tension and the motion of free surface are observed in detail. In the preliminary numerical study of wave-induced vortices near water surface structures, different widths of regular waves are studied in this paper. The wave-induced vortex near the thin plate in depth is observed numerically, and the motion law of the induced vortex near the water surface structure is preliminarily understood. The main innovation of this paper is as follows: 1) A two-phase VOF method is proposed to study the tracing and interaction between different phases of the same fluid in Eulerian coordinate system. A mass conserved Level Set method is proposed, which is successfully applied to the numerical study of dam-break in wet bed. The mass conservation rate of Level Set method is improved effectively. (3) based on the experimental formula, an empirical formula of baffle motion in dam break test is given and applied to the numerical model. In this paper, the influence of baffle motion on the propagation of dam-break water tongue, the evolution of free surface and the impact pressure of rear straight wall are studied systematically.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TV122.4

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