水沙两相流数学模型及其应用

发布时间：2018-06-04 03:40

本文选题：水沙两相流模型 + Eulerian-Lagrangian模型　；参考：《清华大学》2016年博士论文

【摘要】：两相流模型能够较为准确地描述水沙两相间的相互作用,揭示水沙运动机理。构建高精度、适用性强的水沙两相流模型对于完善泥沙运动理论、解决工程泥沙问题有重要的意义。本文旨在完善和发展水沙两相流数学模型,基于Eulerian-Lagrangian观点构建了一个适用于悬移质泥沙运动的颗粒轨道模型;基于Eulerian-Eulerian观点构建了一个可用于大涡模拟的双流体模型,并引入光滑粒子流体动力学(SPH)方法进行求解。论文构建的Eulerian-Lagrangian两相流模型采用包含泥沙体积浓度的雷诺时均控制方程与k-ε紊流模型描述水相运动。视泥沙为分散介质,将泥沙颗粒的运动速度分解为时均流速与脉动速度,采用运动方程计算颗粒时均流速的变化,耦合涡相干模型(EIM)描述泥沙颗粒在紊动水体作用下的脉动。考虑尾流对颗粒紊动的增强效应修正涡相干模型以提高模型模拟悬移质泥沙紊动扩散的精度。基于低含沙浓度假设,简化两相控制方程,得到适用于低含沙水流悬移质输沙问题的Eulerian-Lagrangian两相流模型。将模型应用于二维明渠恒定均匀流悬移质输沙,计算了不同的泥沙粒径条件下悬移质相对浓度垂向分布,讨论了粒径对泥沙扩散系数的影响。结果显示,考虑尾流对颗粒紊动增强效应的Eulerian-Lagrangian模型能够准确模拟较宽粒径范围内的悬移质泥沙的紊动扩散。论文构建的基于SPH方法的双流体模型对连续介质假设下推导的体积平均控制方程组进行空间滤波,采用质量浓度加权的Favre平均得到空间平均的两相控制方程,采用Smagorinsky公式计算亚粒子应力。考虑两相相间作用力、泥沙颗粒粒间作用力以及泥沙对水相亚粒子应力的影响,模型能够较全面地反映水沙两相的相互作用。将含沙水流离散成一组SPH粒子,粒子以水相速度运动并携带两相物理信息。将两相控制方程改写为粒子的运动方程及其携带的物理量控制方程,并采用SPH方法离散求解。将双流体模型应用于静水中抛泥问题,讨论泥沙云团的宽度、下沉速度及浓度分布随泥沙粒径与云团初始体积的变化规律。结果显示,本文构建的双流体模型能够准确描述泥沙云团的运动特性,适用于水沙两相流问题的研究。
[Abstract]:The two-phase flow model can accurately describe the interaction between two phases of water and sediment and reveal the mechanism of water and sediment movement. It is of great significance to construct a high precision and applicable water and sediment two-phase flow model for perfecting the theory of sediment movement and solving the problem of engineering sediment. The purpose of this paper is to perfect and develop the mathematical model of water-sediment two-phase flow, to construct a particle track model suitable for suspended sediment movement based on Eulerian-Lagrangian 's viewpoint, and to construct a two-fluid model which can be used in large eddy simulation based on Eulerian-Eulerian 's viewpoint. The smooth particle hydrodynamics (SPH) method is introduced to solve the problem. The Eulerian-Lagrangian two-phase flow model constructed in this paper uses Reynolds time average control equation including sediment volume concentration and k- 蔚 turbulence model to describe the water phase motion. Considering sediment as a dispersed medium, the motion velocity of sediment particles is decomposed into mean velocity and pulsating velocity, and the variation of average velocity when particles are calculated by the equation of motion. The coupled vortex coherent model (EIMM) is used to describe the pulsation of sediment particles under the action of turbulent water body. Considering the enhancement effect of wake on particle turbulence, the vortex-coherent model is modified to improve the accuracy of simulating the turbulent diffusion of suspended sediment. Based on the assumption of low sediment concentration, the two-phase governing equation is simplified and a Eulerian-Lagrangian two-phase flow model is developed for suspended sediment transport in low-sediment flow. The model is applied to the suspended sediment transport in a two-dimensional open channel with constant uniform flow. The vertical distribution of suspended sediment relative concentration under different sediment particle size is calculated and the influence of particle size on sediment diffusion coefficient is discussed. The results show that the Eulerian-Lagrangian model can accurately simulate the turbulent diffusion of suspended sediment in a wide particle size range. The two-fluid model based on SPH method is used to filter the volumetric average governing equations derived from the continuum medium hypothesis. The two-phase governing equations of the spatial average are obtained by using the mass-concentration weighted Favre average. The subparticle stress was calculated by Smagorinsky formula. Considering the interaction force between two phases, the interaction between sediment particles and the effect of sediment on the stress of subparticle in water phase, the model can fully reflect the interaction between water and sediment. The sediment flow is separated into a group of SPH particles, which move at the velocity of water phase and carry two phase physical information. The two-phase control equation is changed into the motion equation of particles and the governing equation of physical quantities carried by them. The SPH method is used to discretize the solution. The two-fluid model is applied to the slimming problem in hydrostatic water. The variation of sediment cloud width, subsidence velocity and concentration distribution with sediment particle size and cloud initial volume is discussed. The results show that the two-fluid model constructed in this paper can accurately describe the motion characteristics of sediment cloud and is suitable for the study of water-sediment two-phase flow.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O359

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