Two-dimensional numerical simulation of chimney fluidization in a granular medium using a combination of discrete element and lattice Boltzmann methods

Abstract

We present here a numerical study dedicated to the fluidization of a submerged granular medium induced by a localized fluid injection. To this end, a two-dimensional (2D) model is used, coupling the lattice Boltzmann method (LBM) with the discrete element method (DEM) for a relevant description of fluid-grains interaction. An extensive investigation has been carried out to analyze the respective influences of the different parameters of our configuration, both geometrical (bed height, grain diameter, injection width) and physical (fluid viscosity, buoyancy). Compared to previous experimental works, the same qualitative features are recovered as regards the general phenomenology including transitory phase, stationary states, and hysteretic behavior. We also present quantitative findings about transient fluidization, for which several dimensionless quantities and scaling laws are proposed, and about the influence of the injection width, from localized to homogeneous fluidization. Finally, the impact of the present 2D geometry is discussed, by comparison to the real three-dimensional (3D) experiments, as well as the crucial role of the prevailing hydrodynamic regime within the expanding cavity, quantified through a cavity Reynolds number, that can presumably explain some substantial differences observed regarding upward expansion process of the fluidized zone when the fluid viscosity is changed.

DEM investigations of internal erosion: Grain transport in the light of micromechanics

“…-A third option to account for the fluid at the local scale is to use lattice Boltzmann methods (LBMs). 5,11,[24][25][26][27] These methods rely on a statistical physics approach, and Equation 1 is replaced by Boltzmann discrete equation. The fluid behavior is described through a collision-propagation scheme.…”

“…In this paper, REVs of granular materials are considered through a discrete element modeling approach, and fluid/grains interactions are accounted for using a pore network model developed by Chareyre et al This numerical scheme offers a local scale modeling at a relatively cheap computational cost in order to enable fully resolved simulations in three dimensions. This contrasts with most of the approaches found in the literature that either consider 2D problems and introduce a hydraulic radius to recover the connectivity of the fluid phase or use in 3D a nonresolved computational fluid dynamics (CFD) approach …”

“…As a result, Equation has to be changed to account for the local porosity of the granular media. Compared with resolved CFD, unresolved CFD is computationally less expensive and requires no remeshing, but in the meantime, the microscale description of the problem is lost and ad hoc macroscopic assumptions are needed to account for the fluid flow (Darcy's law and Kozeny‐Carman expression for the permeability, for instance). ‐A third option to account for the fluid at the local scale is to use lattice Boltzmann methods (LBMs) . These methods rely on a statistical physics approach, and Equation is replaced by Boltzmann discrete equation.…”

Hydraulic failure of granular materials with artificial cementation

“…More broadly in terms of applications, we present here an investigation on the failure of a cemented granular soil when subjected to localized upward hydraulic flow, a study that can be viewed as an extension of several previous experimental and numerical works on the localized fluidization of purely frictional soils (i.e. soils with zero tensile resistance) where a fluidized cavity expands upward to create a steady vertical chimney [13,[17][18][19][20][21].…”

Future challenges on focused fluid migration in sedimentary basins: Insight from field data, laboratory experiments and numerical simulations

“…Localized fluidization has also been investigated for practical applications such as tapered beds [29], leaking pipes [30] or magmatic intrusions [31]. In this configuration, the fluid is injected through a single nozzle at the base of the granular medium leading, in the fluidization regime, to a stable fluidized cavity or a chimney crossing the whole layer [32][33][34][35]. To our knowledge, however, there has been no quantitative analysis of the morphology of the fluidized zone over long time lapses.…”