对有障碍物影响下的二维重力驱动颗粒泄流进行了简单的实验和数值模拟。根据先前的工作（Zurin { \it et al.，I，物理学\，修订版\，Lett.}，{ \bf 107}：278001，2011），可以通过在适当位置放置圆形障碍物来抑制颗粒排出流的堵塞。为了研究颗粒流中障碍物效应的细节，本文采用颗粒动力学方法。通过实验和数值计算发现，障碍物对出口附近的水平速度分布和填充率有显著的影响。除圆形障碍物外，我们还利用三角形、倒三角形及水平杆形障碍物来讨论颗粒排放流中的障碍物形状效应。通过对颗粒速度分布、颗粒温度、颗粒体积分数等动力学参数的研究，发现三角形障碍物或水平杆可以有效地防止颗粒堵塞。从所得到的结果，我们认为，绕过障碍物周围的颗粒和由此产生的低包装分数在出口区域有效地防止堵塞在一定类别的颗粒排放流。
英文摘要：
We conducted simple experiment and numerical simulation of two-dimensional granular discharge flow driven by gravity under the influence of an obstacle. According to the previous work (Zuriguel {\it et al.,\,Phys.\,Rev.\,Lett.}\,{\bf 107}: 278001, 2011), the clogging of granular discharge flow can be suppressed by putting a circular obstacle at a proper position. In order to investigate the details of obstacle effect in granular flow, we focused on particle dynamics in this study. From the experimental and numerical data, we found that the obstacle remarkably affects the horizontal-velocity distribution and packing fraction at the vicinity of the exit. In addition to the circular obstacle, we utilized triangular, inverted-triangular, and horizontal-bar obstacles to discuss the obstacle-shape effect in granular discharge flow. Based on the investigation of dynamical quantities such as velocity distributions, granular temperature, and volume fraction, we found that the triangular obstacle or horizontal bar could be very effective to prevent the clogging. From the obtained result, we consider that the detouring of particles around the obstacle and resultant low packing fraction at the exit region effectively prevent the clogging in a certain class of granular discharge flow.
Granular flow in a silo demonstrates multiple nonlocal rheological phenomena due to the finite size of grains. We solve the Nonlocal Granular Fluidity (NGF) continuum model in quasi-2D silo geometries and evaluate its ability to predict these nonlocal effects, including flow spreading and, importantly, clogging (arrest) when the opening is small enough. The model is augmented to include a free-separation criterion and is implemented numerically with an extension of the trans-phase granular flow solver described in arXiv:1411.5447, to produce full-field solutions. The implementation is validate…
Granular material is often handled using silos with inserts in industrial processes to prevent "rat-holing" and similar behaviour, optimise mixing behaviour, and prevent segregation. We study the mass flow rate and the static zones of granular silos using the $μ(I)$ rheology in the incompressible Navier-Stokes equations. We also extend the $μ(I)$ model to incorporate pseudo-dilatancy and nonlocal fluidity. We find that insert shape has a significant effect on flow rate and static material. We also find that the effect of inserts on flow rate is not strongly affected by the extensions, while th…
Flow and clogging in a silo with an obstacle above the orifice
在最近的一篇论文中[Zurizes et al.，物理修订版信函107，278001（2011）]已经表明，在出口上方存在障碍物可以显著降低从筒仓倾倒的颗粒物质的堵塞概率。这种减少的量很大程度上取决于障碍物的位置。在这项工作中，我们提出了新的测量来分析不同的出口尺寸，扩展前述的结果，并揭示了障碍物的效果增强作为出口尺寸的增加。此外，研究了障碍物位置对流量特性和拱的几何特征的影响。这些结果加强了以前的证据的压力降低引起的障碍。此外，它示出了如何的平均雪崩大小和平均流速不一定是联系在一起的。另一方面，一个密切的关系，建议之间的平均雪崩大小和流量波动。
On the complexity/criticality of Jamming during the discharge of granular matter from a silo
本文旨在探讨最近关于筒仓卸料问题中自组织临界性、堵塞过程和逾渗理论的比较的讨论[1]。Zurin，A. Garcimartin，D. Maza，L.A.Pugnaloni，J.M.Pastor，“Jamming during the discharge of granular matter from a silo”，Phys.Rev.E 71，051303（2005）].统计阻塞筒仓调查从不同的模型：渗流，自组织临界。
Soft smooth particles in silo discharge show peculiar characteristics, including, for example, non-permanent clogging and intermittent flow. This paper describes a study of soft, low-frictional hydro\-gel spheres in a quasi-2D silo. We enforce a more competitive behavior of these spheres during their discharge by placing an obstacle in front of the outlet of the silo. High-speed optical imaging is used to capture the process of discharge. All particles in the field of view are identified and tracked by means of machine learning software using a MASK R-CNN algorithm. With particle tracking velo…
We examine the gravity-induced flow of dry and cohesionless granular media through an outlet placed eccentrically in a planar silo, employing computations based on a soft-sphere discrete element method. The vertical velocity profiles, measured at the outlet, are self-similar when the eccentricity is given in terms of the gap ($s$) between the wall and the corner of the outlet nearest to the wall. On the other hand, the self-similarity of vertical velocity does not always hold for all eccentricities ($e$) given by the distance between the centers of an outlet and the silo base, which is a typic…
Granular material in a silo with two openings can display a `flow rate dip', where a non-monotonic relationship between flow rate and orifice separation occurs. In this paper we study continuum modelling of the silo with two openings. We find that the $μ(I)$ rheology can capture the flow rate dip if physically relevant friction parameters are used. We also extend the model by accounting for wall friction, dilatancy, and non-local effects. We find that accounting for the wall friction using a Hele-Shaw model better replicates the qualitative characteristics of the flow rate dip seen in experime…
In this paper, we have designed and employed a suspended-wall silo to remove Janssen effect in order to explore directly the local pressure dependence of Granular Orifice Flow (GOF) systematically. We find that as Janssen effect is removed, the flow rate Q changes linearly with the external pressure. The slope α of the linear change decays exponentially with the ratio of the silo size and the size of the orifice Φ/D, which suggests the existence of a characteristic ratio λ (~2.4). When Φ/D > λ, α gradually decays to zero, and the effect of external pressure on the GOF becomes negligible, where…
