Euler-like modelling of dense granular flows: application to a rotating drum

转鼓中的稳态颗粒流：涵盖从凸形到极凹形颗粒形状效应的应力、速度和填充率分布的通用描述

Steady Granular Flow in a Rotating Drum: Universal description of stress, velocity and packing fraction profiles covering grain shape effects from convex to very concave

本研究针对颗粒形状对转鼓稳态颗粒流的影响，构建了解析模型，拓展广义Bagnold标度并引入特征长度，经实验与模拟验证，可通用描述不同颗粒形状下的应力、速度和填充率分布。

Subdiffusive axial transport of granular materials in a long drum mixer

Granular mixtures rapidly segregate radially by size when tumbled in a partially filled horizontal drum. The smaller component moves toward the axis of rotation and forms a buried core, which then splits into axial bands. Models have generally assumed that the axial segregation is opposed by diffusion. Using narrow pulses of the smaller component as initial conditions, we have characterized axial transport in the core. We find that the axial advance of the segregated core is well described by a self-similar concentration profile whose width scales as $t^α$, with $α\sim 0.3 < 1/2$. Thus, the pr…

Continuum theory of partially fluidized granular flows

A continuum theory of partially fluidized granular flows is developed. The theory is based on a combination of the equations for the flow velocity and shear stresses coupled with the order parameter equation which describes the transition between flowing and static components of the granular system. We apply this theory to several important granular problems: avalanche flow in deep and shallow inclined layers, rotating drums and shear granular flows between two plates. We carry out quantitative comparisons between the theory and experiment.

Core Precession and Global Modes in Granular Bulk Flow

A transition from local to global shear zones is reported for granular flows in a modified Couette cell. The experimental geometry is a slowly rotating drum which has a stationary disc of radius R_s fixed at its bottom. Granular material, which fills this cell up to height H, forms a wide shear zone which emanates from the discontinuity at the stationary discs edge. For shallow layers (H/R_s < 0.55), the shear zone reaches the free surface, with the core of the material resting on the disc and remaining stationary. In contrast, for deep layers (H/R_s > 0.55), the shear zones meet below the sur…

Evidence of two effects in the size segregation process in a dry granular media

In a half-filled rotating drum, the size segregation of particles of equal density builds a ring pattern of the large particles, whose location continuously varies from the periphery to the center depending on the size ratio between particles [Thomas, Phys. Rev. E 62, 1 (2000) 961-974]. For small size ratios (typically15): large beads are close to the bottom in a reversing position. The existence of circles with an intermediate radius shows that the segregation at an intermediate level within a flow is possible. In this paper, we experimentally study the segregation of particles of different d…

Boundary Effects on the Angle of Repose in Rotating Cylinders

The angle of repose for the flow of granular materials in a half-filled rotating drum is studied by means of experiments and computer simulations. Particles of different material properties are used to investigate the effects of the end caps on the angle of repose. By fitting the numerical results to an exponentially decaying function, we are able to calculate the characteristic range, $ζ$, of the influence of the wall. We found that $ζ$ scales with the drum radius but does not depend on either the density or the gravitational constant. For increasing particle diameter, finite size effects are…

Hydrodynamics for a model of a confined quasi-two-dimensional granular gas

The hydrodynamic equations for a model of a confined quasi-two-dimensional gas of smooth inelastic hard spheres are derived from the Boltzmann equation for the model, using a generalization of the Chapman-Enskog method. The heat and momentum fluxes are calculated to Navier-Stokes order, and the associated transport coefficients are explicitly determined as functions of the coefficient of normal restitution and the velocity parameter involved in the definition of the model. Also an Euler transport term contributing to the energy transport equation is considered. This term arises from the gradie…

胶体悬浮液可以在非热摩擦颗粒的最小值以下具有非零休止角

Colloidal Suspensions can have Non-Zero Angles of Repose below the Minimal Value for Athermal Frictionless Particles

研究胶体硅颗粒在水填充微流控旋转圆筒中的休止角，探讨热与非热颗粒态的临界过渡。小颗粒热运动促进慢流，堆叠完全平坦，休止角为零；大颗粒在临界尺寸以上停止流动，休止角随颗粒大小增加但低于非热无摩擦颗粒的最小值。

Instabilities in a self-gravitating granular gas

A kinetic and hydrodynamic descriptions are developed in order to analyze the instabilities of a granular gas in the presence of a gravitational field. In the kinetic description the Boltzmann equation is coupled with the Poisson equation, while in the hydrodynamic description the Poisson equation is coupled with the balance equations of mass density, hydrodynamic velocity and temperature for an Eulerian fluid. In the background solution for both descriptions the fluid is at rest with constant mass density and gravitational potential while the temperature depends on time through Haff's law. In…