非球形固体颗粒对弯管内壁的磨损机制

为研究弯管内固体颗粒在液相夹带条件下的运动特性及颗粒对弯管内壁的磨损，采用计算流体动力学与离散元耦合的方法，建立数值模型，考虑固液两相之间的作用，对弯管内的固液两相流动进行数值模拟；通过软件的应用程序编程接口嵌入自编译磨损模型；借助试验结果，验证数值模型的有效性. 结果表明，所建立的数值模拟方案可以准确地模拟颗粒在管内的运动特征并能够预测弯管内壁的磨损位置以及磨损程度. 弯管内的二次流对颗粒运动有重要影响，弯管外侧壁面中心线附近的磨损较严重，磨损的形式以小角度划擦切削为主. 弯管磨损主要与颗粒对壁面的碰撞速度、碰撞角度及碰撞频率有关. 运动中的颗粒与壁面发生多次碰撞，碰撞角度逐渐减小. 随着颗粒球形度的增大，在相同碰撞条件下引起的磨损量变小，但是会降低颗粒的随流性. 颗粒形状影响颗粒在流场中的运动速度以及颗粒与壁面的碰撞. 随着颗粒球形度增大，严重磨损区域向弯管进口方向移动，壁面平均磨损量先减小后增大；当输送颗粒的球形度为0.91时，壁面磨损量最小. 

Mechanisms of Wear of the Inner Wall of the Elbow Pipe Interacting With Non-Spherical Solid Particles

To study the kinetic characteristics of the solid particles involved in the liquid flow in an elbow pipe and wear of the inner wall of the pipe, a numerical work was conducted using the method coupling computational fluid dynamics and discrete element method. The numerical model was established with the interaction between the solid and liquid phases considered. The two-phase flow was simulated thereby. A wear model was developed through the application programming interface of the commercial software EDEM, and the validity of the model was confirmed through the experimental results. The results showed that the numerical scheme could be used to simulate the kinetic characteristics of the solid particles, and to predict the position and extent of wear of the elbow pipe. Along the streamwise direction, the flow velocity near the inner wall continuously decreased, while the flow velocity near the outer wall continuously increased. Starting from the 30° section of the elbow, a pair of symmetrical vortices with opposite rotational directions were produced in the flow passage; the positions of the vortex cores tended to move towards the inner side of the wall, and the intensity of the vortices decreased during this process. The secondary flow in the elbow pipe had a significant influence on motion of particles. Severe wear occurred at the outer side of the wall and near the central line. The difference of wear among different positions of the elbow pipe was mainly affected by the collision velocity, the collision angle, and the collision frequency. As the particles travelled in the pipe, they collided with the wall for multiple times, and the collision angle gradually decreased. The trajectories of the particles exhibited slightly wave patterns. The concept of sphericity was adopted to describe the shape of the particles. As the sphericity increased, the particle shape developed towards the spherical shape, and the amount of the resultant wear under the same collision condition was low, but the capability of the particles of following the liquid movement was undermined. Under the operating condition of the delivery of multiple-shaped particles, in the streamwise direction, the amount of wear firstly increased and then decreased. The amount of wear reached its maximum at the 60o section of the elbow pipe. The wear pattern was dominated by scratches of small angles. Particle shape influenced both the particle velocity in the flow and the collision between particles and the wall. With increasing sphericity, severe wear migrated toward the inlet of the elbow pipe, and the average wear of the wall decreased firstly and then increased. At the sphericity of 0.91 for the delivered particles, the amount of wear attained its minimum.