Abstract:

The CFD-DEM(computational fluid dynamics-discrete element method) coupling calculation method was used to simulate the movement of particles with different particle sizes in the FX-50 hydrocyclone, which analyzed the formation process of the separation field. The continuous phase was obtained by solving the averaged Navier-Stokes equation. The movement of the discrete phase was calculated by the discrete element method. The fluid vlocity and pressure field, particle group velocity, total force, particle-particle and particle-wall contact force was analyzed by Eulerian-Lagrangian method and Freestream drag model. It was shown that the particle velocity loss was relatively large at the confluence of recirculation flow and inlet flow. The particles with diameter of 60μm showed the greatest possibility to accumulate at the cone part of the cyclone and the lowest separation efficiency compared to those particles with diameters of 70μm and 80μm. The variation of the average velocity of the particles experienced the process of decrease first and then increase until its final steady state. The velocity of the particle was larger in the unstable swirl field than that in the stable swirl field vertically. Furthermore, the average vertical speed of particles with 80μm was always greater than that of particles of 60μm and 70μm. In the process of particle-particle and particle-wall contact, the force of the particle was mainly in the normal direction. When the particle was in contact with the wall, the force of contact was the maximum. Due to the instability of the particles trajectory in the early transient flow, the random collisions obviously, resulting in a large fluctuation of the average contact force of the particles. While the fluctuation became unconspicuous when the swirl field reached a steady state.

Key words: CFD-DEM, hydrocyclone, computational fluid dynamics, discrete element method, Eulerian-Lagrangian, Freestream drag model

摘要：

通过CFD-DEM耦合计算方法模拟不同粒径颗粒在FX-50水力旋流器内的运动行为，分析旋流器内旋流分离场的形成过程，连续相的运动采用求解平均化的Navier-Stokes方程得到，离散相的运动通过离散元法计算。采用欧拉-拉格朗日方法，通过Freestream曳力模型传递相间数据，分析了流体的速度场、压力场，颗粒群的速度、受力、颗粒-颗粒和颗粒-壁面的接触作用力。结果表明，当循环流与入口流汇合时，颗粒速度损失较大；当旋流场稳定后，60μm粒径颗粒群在旋流器锥段的堆积最严重，分离速度较70μm、80μm颗粒低；颗粒平均速度的变化为先减小再增大，直到以后的稳定变化。旋流场未稳定时颗粒在竖直方向的运移速度大于旋流场稳定后竖直方向的运移速度，80μm颗粒竖直方向平均速度始终大于60μm和70μm。颗粒-颗粒和颗粒-壁面的接触过程中，颗粒的受力以法向方向为主，当颗粒与壁面接触时，所受合力最大；由于流动前期颗粒在旋流器内运动轨迹不稳定，颗粒随机碰撞明显，导致颗粒平均接触力波动较大，当旋流场达到稳定状态以后，数值改变很小。

关键词: 计算流体力学-离散单元法, 水力旋流器, 计算流体力学, 离散单元法, 欧拉-拉格朗日, Freestream曳力模型