Abstract:

By applying computational fluid dynamics (CFD) method, the large eddy simulation (LES) and Lagrangian particle tracking technology were used to calculate the flow field characteristics in the Rushton turbine stirred tank and the movement behavior of three kinds of St particles. The mean flow field (tangential velocity, axial velocity and radial velocity), particle velocity and concentration distribution were in good agreement with the experiment, which verified the reliability of the numerical simulation. The results showed that the stirred flow field and particle movement presented the characteristics of circulating flow. When the rotation speed N was constant at 313r/min, the small particles of St=0.24 were almost evenly distributed. However, the followability of large particles of St=37.3 with the fluid was poor, the bottom deposition rate was high, and a certain particle blank zone appeared on the top of the vessel. A series of turbulent vortex structures were generated near the impeller, and due to the violent particle-wall collision, the granular temperature at this location was the highest. The migration of small particles (St=0.24) was mainly controlled by the trailing vortices behind the blades, and they were evenly distributed in the low vorticity zone. Due to the large inertia of large particles (St=37.3), their motion was no longer dominated by the vortex, and was quickly thrown to the side wall by the impeller. They passed through the high vortex zone formed by the trailing vortices, so the impeller had a poor agitating effect on nearby large particles.

Key words: stirred vessel, computational fluid dynamics, liquid-solid two-phase flow, vortex structure, numerical simulation

摘要：

基于计算流体动力学（CFD）方法，采用大涡模拟（LES）和拉格朗日颗粒追踪技术计算了Rushton涡轮搅拌槽内流场特性及三种St颗粒的运动行为。平均流场（切向速度、轴向速度和径向速度）、颗粒速度及浓度分布方面与实验值的吻合度较好，验证了数值模拟的可靠性。结果表明，搅拌流场及颗粒运动均呈现循环流特性，当转速N=313r/min不变时，St=0.24的小颗粒几乎实现了均匀分布；而St=37.3的大颗粒与流体的跟随性较差，底部沉积率较高，容器顶部会出现一定的颗粒空白区。叶轮附近产生一系列的湍流涡结构，并且由于剧烈的颗粒-壁面碰撞，该位置颗粒拟温度最高；小颗粒（St=0.24）的运移主要受叶片后方尾涡的控制，均匀分布在低涡量区；而大颗粒（St=37.3）由于具有较大的惯性，运动不再由涡主导，很快被叶轮甩向边壁，穿过了尾涡所形成的高涡量区，故而叶轮对附近大颗粒的搅拌效果较差。

关键词: 搅拌容器, 计算流体力学, 液固两相流, 涡旋结构, 数值模拟