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

气固流中形成的细观颗粒结构研究

基本信息

批准号：
11650175
负责人：
TANAKA Toshitsugu
金额：
$ 2.3万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

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

研究了含颗粒团的气固两相流动。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。采用与单相流相同的SGS模型，采用DNS和LES计算流体运动。固体流动的计算采用拉格朗日方法，在该方法中跟踪单个颗粒的运动，并考虑颗粒之间的碰撞。此外，还对垂直管道中的颗粒沉降流动进行了实验，测量了颗粒团的结构，验证了本文模拟的正确性。研究结果如下：1.本LES和DNS预测的粒子团的形成。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.发现在平均SVF为10 μ m的情况下<-5>，可以观察到颗粒团簇的形成，但需要更长的时间 ...更多信息比高分数的情况下。颗粒团簇的空间尺度随流体粘度的增加而减小。通过对模拟结果中最小涡尺度的检验，发现DNS在当前计算条件下已经达到了预期的效果.结果发现，充分发展的流动建立在管道的下部区域。用激光片层显示技术观察了颗粒团簇在垂直和水平两个平面上的结构。观察到的团簇结构类似于股线网络，与本文的数值预测和之前的循环流化床提升管实验相似。测量了管道横截面中固体体积分数的分布。研究发现，颗粒有向管壁集中的趋势，并且在高固体流量下这种趋势增强.测得的局部SVF的波动模式与目前的预测相似。测得的SVF的概率密度函数分布与预测吻合得很好。测量的SVF的波动功率谱与预测定性一致，但定量，相当不错。少