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

研究了含颗粒团簇的气固两相流动。对周期边界元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。流体运动的计算采用了与单相流相同的SGS模型。固体流动的计算采用拉格朗日方法，跟踪单个颗粒的运动，并考虑颗粒之间的碰撞。在此基础上，进行了垂直管道内颗粒沉积流动的实验，测量了颗粒团的结构，验证了数值模拟的正确性。研究结果总结如下：1.研究成果。目前的LES和DNS预测了粒子团的形成。考察了平均固相体积分数(SVF)和流体粘度对流动结构的影响。结果表明，在平均Svf为10^-lt；-5-gt；的情况下，观察到了粒子团簇的形成，但…所需的时间要长得多比高分数的病例更多。颗粒团簇的空间尺度随流体粘度的增大而减小。我们检查了当前模拟结果中的最小涡旋尺度，发现在目前的计算条件下，DNS已经执行了。结果发现，在管道的下部区域形成了充分发展的流动。利用激光薄片可视化技术观察了颗粒团簇在垂直和水平平面上的结构。观察到的团簇结构类似于线束的网络结构，与目前的数值预测和前人在CFB提升管中的实验结果相似。测量了管道横截面上固体体积分数的分布。研究发现，颗粒有向管道壁面聚集的趋势，且在高固体流率下，这种趋势增强。测得的局地SVF的起伏模式与目前的预测结果相似。测得的SVF的概率密度函数的分布与预测符合得很好。测量的SVF起伏功率谱与预测值在定性上符合，但在定量上是相当好的。较少

Gas-solid flows with particle clusters were studied. Numerical simulations were performed for the gas-solid flows in a rectangular-parallelepiped calculation domain surrounded by periodic bound-aries. Fluid motion was calculated by using DNS and LES, in which the same SGS model as in single-phase flows was assumed. Solid flow was calculated by the Lagrangian method, in which the motion of individual particles was tracked, with considering particle-particle collisions. Furthermore, an experiment on the granular sedimenting flows in a vertical duct was performed to measure the structure of particle clusters and to validate the present simulation. The results are summarized as follows.1. The present LES and DNS predicted the formation of particle clusters. Effects of mean solid- volume fraction (SVF) and fluid viscosity on the flow structure were examined. It was found that, in the case of mean SVF of 10^<-5>, the formation of particle clusters was observed, but it takes much longer time … More than the higher fraction cases. The spatial scale of particle clusters decreased with increasing the fluid viscosity. We examined the smallest eddy scale in the present simulation results and found that DNS had performed for the present calculation conditions.2. It was found that the fully developed flows were established in the lower region of the duct. The structure of particle clusters in vertical and horizontal planes were observed by using laser-sheet visualization technique. The structure of clusters observed is like a network of strands and similar to both of the present numerical predictions and previous experiments in risers of CFB.Distributions of the solid volume fraction in the duct cross-section was measured. It was found that particles tend to concentrate to duct walls and this tendency is enhanced in high solid flow rate.3. The measured fluctuation pattern of the local SVF is similar to the present predictions. The profile of probability density function of the measured SVF agrees well with the predictions. Power spectrum of fluctuation of the measured SVF agrees qualitatively with the predictions, but quantitatively, fairly well. Less