Long-range wall perturbations in dense granular flows

2014 ◽  
Vol 764 ◽  
pp. 171-192 ◽  
Author(s):  
Pierre G. Rognon ◽  
Thomas Miller ◽  
Bloen Metzger ◽  
Itai Einav
Keyword(s):  
Shear Rate ◽  
Power Law ◽  
Eddy Viscosity ◽  
Granular Flows ◽  
Length Scale ◽  
Local Models ◽  
Plane Shear ◽  
Eddy Viscosity Model ◽  
Non Local ◽  
Dense Granular Flows

AbstractWe explore how the rheology of dense granular flows is affected by the presence of sidewalls. The study is based on discrete element method simulations of plane-shear flows between two rough walls, prescribing both the normal stress and the shear rate. Results confirm previous observations for different systems: large layers near the walls develop where the local viscosity is not constant, but decreases when approaching the walls. The size of these layers can reach several dozen grain diameters, and is found to increase when the flow decelerates, as a power law of the inertial number. Two non-local models are found to adequately explain such features, namely the kinetic elasto-plastic fluidity (KEP) model and the eddy viscosity model (EV). The analysis of the internal kinematics further shows that the vorticity and its associated length scale may be a key component of these non-local behaviours.

A non-local rheology for dense granular flows

2009 ◽  
Vol 367 (1909) ◽  
pp. 5091-5107 ◽  
Author(s):  
Olivier Pouliquen ◽  
Yoel Forterre
Keyword(s):  
Granular Flows ◽  
Constitutive Law ◽  
Local Theory ◽  
Plane Shear ◽  
Static Regime ◽  
Entire Flow ◽  
Non Local ◽  
Inclined Planes ◽  
Inertial Regime ◽  
Dense Granular Flows

A non-local theory is proposed to model dense granular flows. The idea is to describe the rearrangements occurring when a granular material is sheared as a self-activated process. A rearrangement at one position is triggered by the stress fluctuations induced by rearrangements elsewhere in the material. Within this framework, the constitutive law, which gives the relation between the shear rate and the stress distribution, is written as an integral over the entire flow. Taking into account the finite time of local rearrangements, the model is applicable from the quasi-static regime up to the inertial regime. We have checked the prediction of the model in two different configurations, namely granular flows down inclined planes and plane shear under gravity, and we show that many of the experimental observations are predicted within the self-activated model.

scholarly journals Self-diffusion scalings in dense granular flows

Soft Matter ◽  
2021 ◽  
Author(s):  
Riccardo Artoni ◽  
Michele Larcher ◽  
James T. Jenkins ◽  
Patrick Richard
Keyword(s):  
Shear Rate ◽  
Solid Fraction ◽  
Granular Flows ◽  
The Self ◽  
Granular Temperature ◽  
Restitution Coefficient ◽  
Self Diffusion ◽  
Diffusivity Tensor ◽  
Dense Granular Flows

The self-diffusivity tensor in homogeneously sheared dense granular flows is anisotropic. We show how its components depend on solid fraction, restitution coefficient, shear rate, and granular temperature.

scholarly journals Non-local rheology in dense granular flows

2015 ◽  
Vol 38 (11) ◽  
Author(s):  
Mehdi Bouzid ◽  
Adrien Izzet ◽  
Martin Trulsson ◽  
Eric Clément ◽  
Philippe Claudin ◽  
...  
Keyword(s):  
Granular Flows ◽  
Non Local ◽  
Dense Granular Flows

scholarly journals Microrheology to probe non-local effects in dense granular flows

2015 ◽  
Vol 109 (2) ◽  
pp. 24002 ◽  
Author(s):  
Mehdi Bouzid ◽  
Martin Trulsson ◽  
Philippe Claudin ◽  
Eric Clément ◽  
Bruno Andreotti
Keyword(s):  
Granular Flows ◽  
Local Effects ◽  
Non Local ◽  
Dense Granular Flows

Non-Newtonian Natural Convection Along a Vertical Heated Wavy Surface Using a Modified Power-Law Viscosity Model

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
M. M. Molla ◽  
L. S. Yao
Keyword(s):  
Boundary Layer ◽  
Natural Convection ◽  
Shear Rate ◽  
Power Law ◽  
Leading Edge ◽  
Numerical Results ◽  
Wavy Surface ◽  
Viscosity Model ◽  
Length Scale ◽  
Modified Power Law

Natural convection of non-Newtonian fluids along a vertical wavy surface with uniform surface temperature has been investigated using a modified power-law viscosity model. An important parameter of the problem is the ratio of the length scale introduced by the power-law and the wavelength of the wavy surface. In this model there are no physically unrealistic limits in the boundary-layer formulation for power-law, non-Newtonian fluids. The governing equations are transformed into parabolic coordinates and the singularity of the leading edge removed; hence, the boundary-layer equations can be solved straightforwardly by marching downstream from the leading edge. Numerical results are presented for the case of shear-thinning as well as shear-thickening fluid in terms of the viscosity, velocity, and temperature distribution, and for important physical properties, namely, the wall shear stress and heat transfer rates in terms of the local skin-friction coefficient and the local Nusselt number, respectively. Also results are presented for the variation in surface amplitude and the ratio of length scale to surface wavelength. The numerical results demonstrate that a Newtonian-like solution for natural convection exists near the leading edge where the shear-rate is not large enough to trigger non-Newtonian effects. After the shear-rate increases beyond a threshold value, non-Newtonian effects start to develop.

An Accurate Model for Prediction of Turbulent Frictional Pressure Loss of Power-Law Fluids in Eccentric Geometries

2021 ◽  
pp. 1-18
Author(s):  
Vahid Dokhani ◽  
Yue Ma ◽  
Zili Li ◽  
Mengjiao Yu
Keyword(s):  
Power Law ◽  
Pressure Loss ◽  
Eddy Viscosity ◽  
Numerical Study ◽  
Axial Flow ◽  
Drilling Fluids ◽  
Eddy Viscosity Model ◽  
Friction Factors ◽  
Power Law Fluids ◽  
Eccentric Annuli

Summary The effect of axial flow of power-law drilling fluids on frictional pressure loss under turbulent conditions in eccentric annuli is investigated. A numerical model is developed to simulate the flow of Newtonian and power-law fluids for eccentric annular geometries. A turbulent eddy-viscosity model based on the mixing-length approach is proposed, where a damping constant as a function of flow parameters is presented to account for the near-wall effects. Numerical results including the velocity profile, eddy viscosity, and friction factors are compared with various sets of experimental data for Newtonian and power-law fluids in concentric and eccentric annular configurations with diameter ratios of 0.2 to 0.8. The simulation results are also compared with a numerical study and two approximate models in the literature. The results of extensive simulation scenarios are used to obtain a novel correlation for estimation of the frictional pressure loss in eccentric annuli under turbulent conditions. Two new correlations are also presented to estimate the maximum axial velocity in the wide and narrow sections of eccentric geometries.

scholarly journals Eddy Viscosity in Dense Granular Flows

2013 ◽  
Vol 111 (5) ◽  
Author(s):  
T. Miller ◽  
P. Rognon ◽  
B. Metzger ◽  
I. Einav
Keyword(s):  
Eddy Viscosity ◽  
Granular Flows ◽  
Dense Granular Flows

scholarly journals Shear-induced diffusion: the role of granular clusters

2021 ◽  
Vol 249 ◽  
pp. 03035
Author(s):  
Matthew Macaulay ◽  
Pierre Rognon
Keyword(s):  
Granular Flows ◽  
Plane Shear ◽  
Self Diffusion ◽  
Physical Mechanisms ◽  
Dem Simulations ◽  
Starting Point ◽  
Correlated Motion ◽  
Contact Adhesion ◽  
Dense Granular Flows

This paper is concerned with the physical mechanisms controlling shear-induced diffusion in dense granular flows. The starting point is that of the granular random walk occurring in diluted granular flows, which underpins Bagnold’s scaling relating the coefficient of self-diffusion to the grain size and shear rate. By means of DEM simulations of plane shear flows, we measure some deviations from this scaling in dense granular flows with and without contact adhesion. We propose to relate these deviations to the development of correlated motion of grains in these flows, which impacts the magnitude of grain velocity fluctuations and their time persistence.

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