水平滚筒内二元颗粒体系径向分离模式的数值模拟研究

Numerical simulation of radial segregation patterns of binary granular systems in a rotating horizontal drum

发展了考虑法向接触力、切向接触力和力矩、以及滚动摩擦力矩的三维三方程线性弹性-阻尼离散单元模型及计算程序,对薄滚筒内二元S型颗粒体系进行了数值模拟,发现采用本文的数学模型可以准确地预测出滚筒内二元S型颗粒流的分层现象.分析了影响滚筒内颗粒分层的因素,讨论了滚筒转速、颗粒装载率等参数对分层的影响,当转速较高时,滚筒内形成大颗粒在外、小颗粒在内、具有圆形界面的月亮模式,当转速较低时形成具有波浪形界面的花瓣模式,并且随着滚筒转速的逐渐降低,花瓣的数量逐渐增加,数值模拟结果与实验完全符合.模拟还得到了花瓣模式的形成过程:混合均匀的两种颗粒在旋转的过程中很快分离,随后在交界区域相互渗透,造成波动界面,最终形成稳定的花瓣模式.一旦花瓣模式形成,滚筒内的颗粒流动出现明显的波动现象,颗粒流的上表面以上弦、下弦形式不断交替,同时流速也快、慢交替.最后探讨了滚筒内花瓣模式分层运动形成的必要条件及机理.

A 3D throe-equation linear spring-dashpot model considering the normal contact foroe, the tangential contact force, and the rolling friction torque, and the corresponding programs for granular dynamics were developed. The flow and the segregation of the S-type binary granular mixtures in a thin rotating horizontal drum were simulated by using the new model. The influences of the rotation speed and the load of the drum on the pattern formation were discussed. The simulation results show that the pattern formation of the S-type binary granular mixtures in the rotating drum can be predicted accurately. As the rotation speed is high, the moon pattern appears, in which the small particles concentrate in a central core and the large particles distribute in the periphery. As the rotation speed is lowered, the petal pattern is found in thin drums, and the number of petals increases as the rotation speed decreases. The process of pattern formations was obtained by the simulation. As the petal pattern forms, the wavy flow of granules in the drum appears. Finally, the necessary condition and mechanisms of the pattern formation in the thin drums are discussed in the paper.