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

1.垂直通道内气固向下流动的双耦合数值模拟研究了垂直通道内载颗粒向下的湍流流动。用与单相流相同的模型用LES模拟流体运动，用拉格朗日方法模拟单个粒子的运动。考虑了粒子间的碰撞。模拟结果表明，颗粒对流体湍流度有一定的影响，但定量结果与实测结果不一致。结果表明，即使在0（10-4）量级的粒子体积分数较低时，粒子对撞对粒子扩散的影响也很大，粒子横向波动速度的预测值是没有粒子对撞时的2倍。预测的粒子涨落速度与Kulick et al.（1994）的实验结果吻合得很好。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。结果表明，颗粒有向低速条带集中的趋势。粒子簇的结构LES的结果表明，粒子容易形成由条纹结构引起的粒子云。已知当颗粒浓度增加时，颗粒会形成密集的团簇，并对湍流结构产生很大影响。对颗粒团簇的结构进行了数值模拟。在二维场和三维场中都发现了特征结构。结果表明，颗粒粒径越大，簇的空间尺度越大。

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.