Development of parallel computational method for granular mixtures transported by turbulent flows

了解非均匀推移质颗粒分离的物理过程是很重要的，因为非均匀推移质颗粒由不均匀的直径和密度组成。本研究的目的是发展一种计算方法来预测非均匀颗粒的湍流传输和它们的分离。研究的关键技术是处理颗粒间接触力的离散单元法(DEM)、液-固双向湍流模型和处理大量颗粒的并行计算方法。他们的联系人。(2)包括固体在内的湍流液体流动。颗粒采用液-固两相湍流模型。(3)在液固湍流模型中考虑了液固两相之间的相互作用。(4)基于区域分解方法的并行计算方法使我们能够处理大量的粒子。(5)用曲线坐标表示每个子域的几何形状，适用于形状复杂的边界。(6)颗粒路径线技术等数值可视化方法使我们能够更好地了解颗粒各组分的流动形态，所开发的计算方法被应用于各种问题，如旋转圆柱体中的颗粒混合物、振荡液体流动中颗粒的不均匀分布、水工建筑物前方出现的颗粒分离等，证实了颗粒分布的预测值与实验结果吻合较好，由于采用了并行计算，计算效率令人满意。

It is important to understand the physical process on the segregation of the non-uniform bed-load particles, which consist of non-uniform diameters and densities. The purpose of this study is to develop a computational method to predict turbulence transportation of the non-uniform particles and their segregation. The key techniques of this study are distinct element method (DEM) to treat contact forces among particles, liquid-solid two-way turbulence model and a parallel computation method to deal with large number of particlesThe developed computational method is characterized by the following items : (1) The employment of DEM allows us to predict 3D translational and rotational motions of particles as well as. their contacts. (2) The turbulent liquid flows including solid. particles are modeled with a liquid-solid turbulence model. (3) The interaction between liquid and solid phases is taken into account in the liquid-solid turbulence model. (4) A parallel computational method based on a domain decomposition method enables us to deal with a large number of particles. (5) The curvilinear coordinates are utilized to represent the geometry of each subdomain and it is applicable to complicated-shaped boundaries. (6) The numerical visualization methods, such as a particle pathline techniques, allows us to understand the flow patterns of each component of particles.The developed computational method was applied various problems, such as a granular mixture in a rotating cylinder, non-uniform particles under oscillating liquid flows, particle segregation arising in front of hydraulics structures Generally, it was confirmed that the predicted particle distributions agree with experimental results and that computational efficiency is satisfactory due to the parallel computation.