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

了解由非均匀粒径和密度组成的非均匀床载颗粒的偏析的物理过程具有重要意义。本研究的目的是建立一种计算方法来预测非均匀粒子的湍流输运及其偏析。本研究的关键技术是处理颗粒间接触力的离散元法（DEM）、液固双向湍流模型和处理大量颗粒的并行计算方法。所开发的计算方法的特点是：(1)利用离散元法可以预测颗粒的三维平移和旋转运动，以及颗粒的三维运动。他们的联系人。(2)湍流液体流动包括固体。采用液固湍流模型对颗粒进行建模。(3)液固湍流模型考虑了液固两相的相互作用。(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)采用曲线坐标表示各子域的几何形状，适用于形状复杂的边界。(6)数值可视化方法，如粒子路径技术，使我们能够了解粒子各组分的流动模式。将所建立的计算方法应用于旋转筒体中颗粒混合、振荡液体流动中颗粒不均匀、水力学结构前颗粒偏析等问题，结果表明，预测的颗粒分布与实验结果吻合较好，并且由于并行计算，计算效率较高。

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.