Study on the 3-D Spatial Structure of Particle Cluster

研究了气固两相流中颗粒团簇的时空结构。对垂直管道中的重力沉降流进行了实验研究。利用高速摄像机拍摄的管道截面颗粒分布时间序列，重建了管道内颗粒团的空间和时间三维结构，并对颗粒团的三维空间结构进行了数值模拟.对周期边界包围的矩形-平行六面体计算区域内的气固两相流动进行了数值模拟。流体运动采用DNS计算，固体运动采用考虑颗粒碰撞的拉格朗日模型计算。在最大的情况下，跟踪了超过一千六百万个粒子。(1)粒子分布的三维时空结构 关于我们 从实验中获得。结果发现，三维呈现的颗粒分布，使我们能够找到的三维性质的颗粒团。(2)通过对颗粒浓度空间分布功率谱的分析，定量研究了颗粒团的空间尺度特性。结果表明，团簇由多个空间尺度组成，但以低波数、大尺度结构为主。(3)提出了一种基于波数空间低通滤波技术的颗粒团三维空间结构重建方法，并将其应用于数值模拟获得的流场数据。成功地提取了颗粒团的主要三维结构。这使得对其三维结构和行为的详细研究成为可能。我们发现在二维观测中可以识别的反U结构是弯曲管状团簇元的一部分。在三维空间中，这些集群元素以非常复杂的方式相互作用。少

Spatial and temporal structure of particle clusters formed in gas-solid flows is studied. Experiments are made for gravitational settling flow in a vertical duct. Spatial and temporal three-dimensional structure of particle clusters formed in the duct are reconstructed from the measured time series of high-speed camera images of particle distributions in a duct cross-section.In addition, numerical simulations are conducted to investigate the three-dimensional spatial structure of particle clusters. The numerical simulations are made for the gas-solid flows in a rectangular-parallelepiped calculation domain surrounded by periodic boundaries. The fluid motion is calculated by using DNS, while the solid flow is calculated by using a Lagrangian model with considering the particle-particle collision. More than sixteen million particles are tracked in the maximum case.The obtained results are summarized as follows.(1) Three-dimensional spatial and temporal structure of particle distributions … More are obtained from the experiments. It is found that three-dimensional presentation of particle distributions enables us to find the three-dimensional nature of particle clusters.(2) Spatial-scale characteristics of particle clusters were investigated quantitatively by analyzing the power spectrums of spatial particle concentration distributions obtained by the present simulation. The results showed that the cluster consists of multiple-spatial scales while the low wave-number, hence large-scale structure, is dominant.(3) A reconstruction method of three-dimensional spatial structure of particle clusters based on the low-pass filtering technique in the wave-number space are proposed and applied to the flow field data obtained from the present numerical simulations. Dominant three-dimensional structures of particle cluster are successfully extracted. It becomes possible to have the detailed investigations on its three-dimensional structures and behaviors. We found that inverse U-structure which is recognizable in two-dimensional observations is a part of bent tube-like cluster elements. In three-dimensions, these cluster elements are interacting in a very complex way. Less