Numerical Analysis of the Structure of Gas-Solid turcbulene by Using LES

1.垂直槽道内向下气固两相流动的大涡模拟对垂直槽道内向下含颗粒的湍流流动进行了双向耦合的数值模拟。流体运动采用大涡模拟，模型与单相流相同，颗粒运动采用拉格朗日方法。考虑了颗粒间碰撞的影响.模拟结果表明，颗粒对湍流有一定的影响，但在定量上与测量结果并不一致.模拟结果表明，即使在颗粒体积分数为O（10-4）量级的低颗粒浓度下，颗粒间碰撞对颗粒扩散的影响也很大，粒子在横向的涨落速度是没有粒子-粒子碰撞时的两倍，与Kulick等（1994）的实验结果符合得很好。通过对计算流场的可视化，研究了颗粒分布与条纹结构之间的关系。大涡模拟结果表明，颗粒在低速时容易向低速条纹聚集。2.颗粒团簇的结构大涡模拟结果表明，由于条纹结构的存在，颗粒容易形成颗粒团簇。颗粒浓度增加时，颗粒形成密集的团簇，对湍流结构有很大的影响。对粒子团的结构进行了数值模拟。在二维和三维场中均发现了团簇的特征结构，团簇的空间尺度随粒径的增大而增大。

1.LES of downward gas-solid flows in a vertical channelNumerical smuations with two-way couping were performed for downward particle laden tutbulent flows in a verticul channel. Fluid motion was culculated by using LES with the same models as in single phase flows and the motin of individual particles by the Lagrangian method. Particleparticle collisin was taken into considertion.The present simulation showed that fluid turbulence is modified by particles but quantitatively did not get a good agreement with the measurement.It was found that the effects of particle-particle collisinon on particle diffusion is large even at low ppaticle volume fraction of the order O (10-4), and that the predicted paticle fluctuation velocity in transverse direction is as two times as that without particle-particle collisimon.the predicted particle fluctuation velocies agreed well with the experiment by Kulick et al. (1994). By visualizing the calculated flow field the relation between the particle distribution and the streak structure was studied. It was found that particles tend to concentrate to the low speed streaks.2.Structure of paticle clusterThe results of LES shown that particles tend to form particle clauds caused by the streak structure. It is known that particles form dense clusters and affect turbulent structure largely when particle concentration increases. The structure of particle cluster is also simulated numerically. The characteristic structures both in two-dimensional and three dimensional fields were found. It was found that the spatial scale of cluster increases with increasing particle diameter.