Dispersion of particles by spontaneous interparticle percolation through unconsolidated porous media

12 pagesInternational audienceWe have performed extensive experimental and numerical studies of spontaneous percolation of small beads through an unconsolidated porous media made with large glass beads. In this paper, an experimental setup and a fast "discrete element method" algorithm are presented to deal with large numbers of particles during our interparticle percolation phenomenon studies. In all the experimental and numerical analyses, the size ratio between the moving beads and the stable packing was chosen larger than the geometrical trapping threshold: ξc=((2/(√3−1))^−1=6.464.... We measure the longitudinal and transverse dispersion coefficients versus the height of the porous medium or the number of falling small beads. The influence of bead properties such as density, diameter, or restitution coefficients was investigated by using either steel or glass beads. The individual description of these effects and their explanations were made possible by confrontation and coupling between experimental and numerical results. Indeed, with our numerical model, individual analysis of the effects of these mechanical or geometrical parameters were made possible and carried out

Transit time during the interparticle percolation process

International audienceA numerical investigation of jamming effect during the spontaneous interparticle percolation process of small beads through an unconsolidated porous media has been performed. The size ratio between the moving beads and the ones building up the porous medium was chosen larger than the geometrical trapping threshold: ξc=(2/√3−1)−1=6.464.... In this paper, we used the discrete element method algorithm to study the rebounds of particles on the top of the porous medium and the transit times of an assembly of particles through it. Several parameters such as the number of injected particles, the size ratio between beads, and the energy restitution coefficient are investigated. This study leads to give some important results of the evolution of the transit time versus the contiguous volume occupied by the percolating particles

A coupled discrete element - lattice Boltzmann method to investigate internal erosion in soil

International audienceIn this paper, we present a coupled Discrete Element (DE) and Lattice Boltzmann (LB) method to model fluid-solid interactions. This method is applied to study and model a two-dimensional piping erosion through a set-up inspired by the Hole Erosion Test (HET). In this work, we mainly focus on grain detachments under hydraulic loading. Simulation results show that the erosion law classically used in such experiments, can be retrieved with our model. It illustrates that such coupled systems can be investigated with the LB-DE approach developed in this work. This approach is a promising tool which is well designed to perform such investigations at the grain scal

Ecoulements de particules dans un milieu poreux

This work deals with experimental and numerical investigations on particles flow through a packing of larger spheres.We built an experimental device to study lateral dispersion and the mean transit time of a blob of particles through a porous medium. Particularly, we determined the dependence of the mean transit time on the number of particles, on particle size and on the height of the porous medium. We also characterized the dependence of the lateral dispersion coefficient on the number of particles moving in the porous structure.Then, we developed numerical simulation models based on "Event-Driven" and "molecular dynamic of soft spheres" methods. Those allowed us to supplement the experimental study by analyzing the influence of various additional parameters. The access inside the porous medium allowed a finer analysis of particles dispersion.Finally, we approached the possibility of using the spontaneous percolation phenomenon to produce a mixer. Thanks to the numerical tool, we carried out and characterized mixtures of particles of different sizes. We showed that this process proves to be a simple and effective method to obtain homogeneous mixtures of particles.Cette thèse a pour objet l'étude expérimentale et numérique de l'écoulement de particules dans un empilement de sphères plus grosses. Un dispositif expérimental a été mis au point pour étudier la dispersion latérale et le temps moyen de séjour d'un paquet de particules dans un milieu poreux. Nous avons en particulier déterminé la dépendance du temps moyen de transit en fonction du nombre de particules en écoulement, de la taille des particules et de la hauteur du milieu poreux. Nous avons également caractérisé la dépendance du coefficient de dispersion latéral vis-à-vis du nombre de particules transitant dans la structure poreuse.Dans un deuxième temps, nous avons développé des modèles de simulations numériques basés sur les méthodes "Event-Driven" et "dynamique moléculaire de sphères molles". Ceux-ci nous ont permis de compléter l'étude expérimentale en analysant l'influence de divers paramètres supplémentaires. L'accès à l'intérieur du milieu poreux a permis une analyse plus fine de la dispersion des particules. Enfin, nous avons abordé la possibilité d'utiliser le phénomène de percolation spontanée pour réaliser un mélangeur. Grâce à l'outil numérique, nous avons réalisé et caractérisé des mélanges de particules de tailles différentes. Nous avons alors montré que ce procédé s'avère être un moyen simple et efficace pour obtenir des mélanges homogènes de particules

Stokes Flow Within Networks of Flow Branches

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Particle percolation through a porous medium

International audienceIn this paper we study transport of particles due to gravity in a porous medium simulated by a packing of large beads. We determine the dependency of the mean transit time for different percolating particle batches and for different packing heights. We compare our results with numerical simulations based on the Discrete Element Method to extend experimental studies and to analyze the part play by the coefficient of restitution and the aspect ratio between the two size of beads

Transport of small particles through a 3D packing of spheres: experimental and numerical approaches

In this paper, we study the transport of particles through a porous structure. Experimentally, we focus our attention on the dependence of the mean transit time on some parameters like the number of small particles injected in the structure, and the height of the packing. We have developed a numerical model, based on a DEM method, to simulate the experiment. This model is useful for accessing the internal structure of the packing and for analysing precisely the influence of the restitution coefficient and the size ratio between spheres

Two-scale analysis of the permeability of 3D periodic granular and fibrous media

International audienceIn this paper, a numerical study of slow flow through a filter viewed as a porous medium made of arrays of cubic solid particles or solid fibers of square cross section is considered. A double-scale asymptotic method is used to determine a system of equations that are then solved numerically to calculate the permeability. Simulations are made at the REV scale, and macroscopic properties are deduced. At the microscale, three arrangements (simple cubic, body-centered cubic and face-centered cubic) are analyzed. A parametric study is carried out, for both granular and fibrous cases, showing the porosity evolution with the size ratio between the solid particles and the periodic cell. At the macroscopic scale, the interest of this analysis is to compute the Darcy's permeability of such arrays as a function of the porosity and the packing characteristics. Results are given over the full porosity range for SC, BCC and FCC arrays. On the other side, the microscopic analysis shows the influence of particle or fiber arrangement and size on the fluid velocity and the pressure field inside the porous structure

Performance prediction of filters with rectangular fibers using coupled lattice Boltzmann and discrete element methods

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