Numerical Analysis of Meso-Scale Particle Structure formed in Gas-Solid Turbulence

1.垂直流道中气固两相下行流动的LBS数值模拟采用双向耦合的方法对垂直流道中的下行颗粒管状流动进行了数值模拟，其条件与斯坦福大学的数值模拟结果相一致。流体运动的计算采用与单相流相同的大涡模拟方法，单个颗粒的运动采用拉格朗日方法。考虑了颗粒-颗粒间的胶合作用。将滤波法应用于气相流场，研究了大涡模拟的网格分辨率对颗粒扩散的影响。网格分辨率的影响与斯托克斯数相关，斯托克斯数由颗粒的松弛时间与流体涡旋与颗粒相互作用的时间之比定义。提出了颗粒运动的大涡模拟网格分辨率判据。在此基础上，对实验中使用的三种颗粒进行了大涡模拟。目前的双向耦合模拟预测了颗粒在近壁区倾向于向高速条纹集中。而以前的单向耦合模型则预测了相反的趋势，预测的通道中心区域的粒子云图与实验符合得很好。颗粒团团结构对二维循环床内颗粒团簇结构进行了数值模拟，模拟结果表明，考虑Chanel壁的颗粒团簇尺寸比没有Chanel壁影响的颗粒团簇尺寸小，颗粒大小分布对颗粒团簇大小的影响较小。

1. LBS 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, of which conditions corrspond to those by a group of Stanford University.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.Particle-particle collisin was taken into considertion.First, the effect of grid resolution of LES on the particle diffusion was investigated by appling filtering to gas-flow fields.The effect of grid resolution was correlated with Stokes number defined by the ratio of particle's relaxation time to the interaction time between a fluid eddy and a particle.An criterion of grid resolution of LES for particle motion was proposed.Subsequently, LES of gas-solid flows was performed for three kinds of particles used in the corresponding experiment.The present simulations with two-way coupling predicted that particles tend to concentrate to high-speed streaks in the near-wall region, while the previous ones with one-way coupling predicted the contrary tendency.The predicted patterns of particle clauds in the channel-center region agree well with the experiment.2. Structure of paticle clusterThe structure of particle cluster in a two-dimensional circulation fluidized bed is also simulated numerically.The simulation taking account of the chanel walls predicted smaller claster size than that without the effect of the chanel walls.It was found that the effect of particle size distribution on the scale of clusters is small.