转鼓中双组元颗粒混合物形成斑图的模式和机制

Patterns formative model and mechanism of binary granular mixtures in a thin rotating drum

双组元颗粒混合物在薄转鼓中形成花瓣斑图的物理现象引起了学术界的关注,实验研究和理论分析已逐渐揭示出花瓣形成过程的复杂行为。本研究受波破裂模型的启发,通过开展一系列双组元颗粒混合物在转鼓中形成花瓣斑图的实验研究,得出如下结论:1)颗粒混合物在流动层中的混合—分聚竞争及与之相伴的波破裂行为是斑图形成过程的重要动态平衡特征,提出的"双重波破裂模式"可描述前半花瓣和后半花瓣形成过程的不同动力学特征;2)颗粒沉积结构对流动状态具有记忆效应并作为来流的初始条件在循环运动中起到正反馈作用,强化了花瓣结构的周期性演化过程。花瓣斑图的形成机制可简要地归结为:自发分聚,耦合强化;3)在形成规则花瓣斑图的转速范围内,花瓣数量随转鼓转速提高而减少,而与转鼓尺寸及不同组元颗粒物性间的复杂关系仍有待深入研究。

The phenomenon of patterns formation of binary granular mixtures in a thin rotating drum has aroused the concern of academics, and experimental research and theoretical analysis on the forming process reveals the complex behaviour. In the present paper, on the basis of the inspiration by wave breaking model, the authores conducted a series of experimental research on the physical mechanisms of pattern formation. Conclusions are drawn as follows： （1） the competition of mixing-demixing between components of binary granular mixture and the associated wave breaking behaviours in flowing layer are the important dynamic features, and “the double wave breaking model” describes the different dynamic characteristics of the formation processes of the first half and the second half petal; （2） the particle deposition structure memorizes the granular flowing state and subsequently as initial conditions of the circulation flow plays a positive feedback mechanism, so it strengthens periodic evolution process with the petal structure. Petal pattern formation mechanism can be briefly summed up as： spontaneous segregation and coupling strengthening; （3） in the rotation speed range of forming regular petal pattern, the number of petals increases with the decrease of drum rotation speed, and the complex relationship of the number of petals between the rotating drum sizes and different components of granular mixtures remains to be further studied.