Granular flows through converging sections such as conical hoppers have been reported to be submitted to instationarities, which in certain circumstances can appear to be organized and periodic. In this paper, we explore this phenomenon by conducting discrete element modelling simulations of a 3D gravity-driven hopper flow and varying a large number of parameters such as hopper geometry and granular sample properties. Dedicated postprocessing techniques are developed and used to investigate the spatial and temporal patterns of these instationarities and to bring some understanding on the physics of this spontaneous phenomenon. Numerical results show that a clear structure appears for these instationarities, under the form of rapidly propagating waves relating variations in velocity magnitude and coordination number. While very faint, periodic variations of the sample density are also detected. The parametric study reveals that the self-organization of these variations requires a narrow set of conditions in terms of hopper geometry and intergranular contact friction coefficient.

中文翻译：

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锥形料斗中颗粒流的周期性不平稳性

据报道，流经诸如锥形漏斗之类的会聚部分的颗粒流易受平稳性的影响，在某些情况下，平稳性似乎是有组织的和周期性的。在本文中，我们通过对3D重力驱动的料斗流量进行离散元素建模仿真并更改大量参数（例如，料斗几何形状和颗粒样品属性）来探索这种现象。开发了专用的后处理技术，并将其用于研究这些不平稳现象的时空模式，并对这种自发现象的物理原理有所了解。数值结果表明，在与速度大小和配位数相关的快速传播波的形式下，这些平稳性出现了清晰的结构。虽然很晕 还可以检测到样品密度的周期性变化。参数研究表明，这些变化的自组织需要在漏斗几何形状和晶间接触摩擦系数方面狭窄的条件。