【作者】 刘杨；

【导师】 邵雪明；

【作者基本信息】 浙江大学 ， 流体力学， 2006， 硕士

【摘要】 粒子悬浮流在自然界和各种工业应用中普遍存在，例如江河、水库中泥沙的沉积和输运，破坏力巨大的沙尘暴以及流化床内的气固流动，管道内的气力输送和锅炉燃烧室里的煤灰和空气的混合燃烧等。粒子沉降是悬浮流的一种，粒子沉降特性的研究工作早在20世纪60年代就开始兴起，直到现在已经在这一领域的某些方面取得了一系列成果。而直接数值模拟方法，可以经济、直接、准确的给出粒子沉降的规律，是研究的一种重要手段。基于分布式拉格朗日乘子的虚拟区域方法(DLM／FD)是近年来出现的直接数值模拟粒子流的新方法之一。其基本思想是：通过假设流体也充满粒子占据的空间，这样把一个几何复杂区域内的问题扩展到一个相对大的，但几何简单的区域中，控制流体流动的N-S方程和控制粒子运动的刚体运动方程通过无滑移边界条件和作用在粒子上的力和力矩耦合在一起进行求解，而刚体运动的限制则通过一个拉格朗日乘子来施加。这样在计算时不但作用在粒子上的力和力矩不需要再显式计算，同时也可以应用固定的结构化网格和快速求解算法，避免了计算过程中重新更新和划分网格的需要。 本文在简单介绍基于分布式拉格朗日乘子的虚拟区域方法的基础上，并应用这一方法对单个的二维哑铃形粒子和三维的椭球粒子进行了数值模拟。研究哑铃形粒子在不同雷诺数和不同初始状态以及不同初始释放位置下的沉降性质，并将模拟结果和实验结果进行了对比，检验了数值方法的合理性；然后，又用该方法模拟了椭球粒子的沉降运动，分析了不同雷诺数下相同长短轴比的椭球粒子的沉降轨迹、角度变化和尾涡变化以及同一雷诺数下不同长短轴比的椭球粒子的沉降性质。最后总结出哑铃粒子和椭球粒子的沉降规律。更多还原

【Abstract】 Particulate flows are commonly encountered in various natural phenomena and industrial processes, such as the motion of sand in the river and reservoir, the sandstorm in the nature, as well as the transportation of solid particles and gas in the pipeline. The sedimentation of particles is one of the particulate flows. Research on sedimentation of particles began as early as in the middle of the 20^th century. Direct numerical simulation （DNS） method is one of the important methods for the particulate flows. Distributed Lagrange multiplier/fictitious domain （DLM/FD） method is a promising new DNS method for the particulate flows. The basic idea of DLM/FD method is to imagine that interior space of the solid is filled with the same fluids as outside, and the fluids inside, and on solid boundary is constrained to move at the same velocity of the solid by using a distributed Lagrange multiplier. Thus a problem on a geometrically complex domain can be extended to a larger, simpler domain, which allows a fixed structured mesh can be used for the entire computation, and eliminates the need for repeated remeshing and projection.In this paper, the DLM/FD method was simply introduced, and the DLM/FD method was used to simulate the sedimentations of a single dumbbell-like particle and a single ellipsoid particle in a vertical channel. The behaviors of sedimentation of a single dumbbell-likep particle in different Reynolds numbers and in the different initial conditions were both included in the research. The behaviors of sedimentation of a single ellipsoid particle in different conditions were involved in the consideration. In order to validate the DLM/FD method, the results of DNS method were compared with experimental results in this paper. In the end, the rules of the sedimentation of the particles were given.更多还原