Study on the Control of Meso-Scale Particle Structure formed in Gas-Solid Flow

为了对聚类流的流动控制进行基础研究，研究了粒径分布对聚类流结构的影响。在周期边界包围的矩形-平行六面体计算域中对气固流动进行了数值模拟。流体运动采用DNS计算，固体流动采用考虑粒子碰撞的拉格朗日模型计算。此外，本文还对垂直管道中的颗粒沉降流进行了实验，以测量颗粒团簇的结构，并验证了本文的模拟结果。在实验中，用激光片可视化设备测量了团簇的空间结构，用光纤粒子浓度测量系统测量了固体体积分数的时间序列，用相位多普勒风速仪测量了气体和粒子的速度。所得结果总结如下：(1)在有粒径分布的情况下，本数值模拟得到的团簇比无粒径分布的团簇大。此外，粒径分布减小了局部固体体积分数的波动。(2)相应实验的测量结果表明，考虑粒径分布的数值模型对团簇结构的预测效果优于不考虑粒径分布的数值模型。(3)在数值模拟中，颗粒团簇的发展在很大程度上受到粒径分布的抑制。认为这种对团簇发展的抑制是由粒径分布引起的粒子速度波动引起的粒子扩散引起的。(4)目前的数值模型预测，颗粒越大，团簇越大。

To make the basic study for the flow control of clustering flows the effects of particle size distribution on the structure of the clustering flow is studied. Numerical simulations are performed 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. Furthermore, an experiment on the granular sedimentation flows in a vertical duct is performed to measure the structure of particle clusters and to validate the present simulation. In the experiment, the spatial structure of clusters are measured by a laser-sheet visualization equipment, the time series of solid volume fraction by a fiber-optic particle concentration measuring system, the velocities of the gas and the particles by a phase Doppler anemometer.The obtained results are summarized as follows.(1) In the case with particle size distribution, the present numerical simulation gives the larger clusters compared with those without particle size distribution. In addition, the particle size distribution reduces the fluctuation of the local solid volume fraction.(2) The measurement of the corresponding experiment demonstrated that the present numerical model with particle size distribution gives the better prediction about the cluster structure than that without it.(3) In the numerical simulation, the development of the particle clusters is much suppressed by the effect of the particle size distribution. It is considered that this suppression of the cluster development is caused by the particle diffusion due to the particle-velocity fluctuation made by the size distribution.(4) The present numerical model predicts that the larger particles make the larger clusters.