颗粒相流动边界条件对其浓度分布的影响机制  

MECHANISM OF INFLUENCE OF FLOW BOUNDARV CONDITIONS OF PARTICLE PHASE ON ITS CONCENTRATION PROFILE

作　　者：祁海鹰[1] 李宇红[1] 由长福[1] 刘双科[1] 徐旭常[1] 

机构地区：[1]清华大学煤的清洁燃烧技术国家重点实验室,北京100084

出　　处：《力学学报》2001年第5期601-611,共11页Chinese Journal of Theoretical and Applied Mechanics

基　　金：国家重点基础研究专项经费资助项目(G19990222)

摘　　要：运用描述颗粒相内部作用力的离散介质动力理论和“双流体”欧拉方法对循环流化床中 的稠密气固两相流动进行了数值模拟，并专门研究了颗粒边界条件对其在近壁区浓度分布的影 响，探讨了产生畸变的机制；比较和检验了相关的理论模型．研究表明，近壁区颗粒轴向速度 梯度大小；和在那里局部加密的计算网格，对颗粒浓度的径向分布有强烈的影响，导致浓度分 布畸变的原因是不合理的边界条件过高估计了当地颗粒的脉动强度．提出选择边界条件的原则 是允许颗粒在壁面上有一定程度的滑移．In this paper a simulation of the dense gas-solid two-phase flow in circulating fluidized bed reactor (CFB) has been performed in the frame of Eulerian approach. The kinetic theory of granular medium has been used to describe interactions within the particle phase. The typical flow pattern in CFB── “annular-core” ──has been predicted correctly by the simulation, i. e. the particle concentration in the central region of the reactor riser is low and increases monotoinally to the wall and reaches the maximum there. Compared with experiments, however, it has been found that an unexpected peak of the radial particle concentration profile appears in the region near the wall, but not at the wall, as experimentally observed in most of investigations. This is obviously an un-real and unreasonable phenomenon. According to literature two processes should be considered in the wall region due to strong interactions within the particle phase, as well as between particles and wall under the dense con- dition. One of them is the dissipation of particle fluctuating energy caused by unelastic collisions. Particle reflection from the wall after collision is weakened. Another one is the energy production caused by the particle velocity gradient resulted from shear viscosity. If the latter dominates, it is possible to form a thin layer with a low particle concentration at the wall. In the simulation the calculated particle concentration profile depends on the theoretical models by which the effect of energy production is obviously overestimated. Because unsuitable boundary conditions──the zero gradient of particle fluctuation energy (i.e. granular temperature) and zero particle velocity at the wall──has been used, namely only energy production mechanism is accounted for, the predictions on particle fluctuation energy and solid pressure are too high. As a normal stress produced by particle collision the solid pressure plays a repelling roll to prevent from exceeding the maximal particle volume fraction under the de

关 键 词：边界条件 浓度分布 稠密气固两相流动 欧拉数值模拟 

分 类 号：O359[理学—流体力学]