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

为了对聚集流的流动控制进行基础研究，研究了颗粒尺寸分布对聚集流结构的影响。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。流体运动采用数值模拟，固体流动采用考虑颗粒-颗粒碰撞的拉格朗日模型。在此基础上，进行了垂直管道内颗粒沉降流的实验，测量了颗粒团簇的结构，验证了数值模拟的正确性。在实验中，用激光薄片可视化设备测量了团簇的空间结构，用光纤颗粒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颗粒的速度，得到了如下结果：(1)在有颗粒分布的情况下，数值模拟给出了较大的团簇。此外，颗粒尺寸分布减小了局部固体体积分数的波动。(2)相应实验的测量表明，考虑颗粒尺寸分布的数值模型比没有颗粒尺寸分布的数值模型对团簇结构的预测更好。(3)在数值模拟中，颗粒尺寸分布的影响对颗粒团簇的发展有很大的抑制作用。这种对团簇发展的抑制是由于粒子团的尺寸分布引起的粒子速度起伏引起的粒子扩散所致。(4)本数值模型预测，较大的粒子会形成较大的团簇。

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.