Morphodynamics during air injection into a confined granular suspension

Chevalier, Christophe; Lindner, Anke; Leroux, Maxime; Clément, Éric

doi:10.1016/j.jnnfm.2008.07.007

Cited by 53 publications

(82 citation statements)

References 42 publications

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“…Finally, a new regime was reported in the 2D experiment, with a transition between the growth of an air finger and the fracture of the above granular layer at a given height in the cell. Such patterns as fingering and fracturing have been reported in the literature in deformable, saturated porous media, when varying the grain volume fraction [40,55,56]. These patterns, however, were mainly described for horizontal Hele-Shaw cell, in which buoyancy does not govern the system dynamics.…”

Section: Discussionmentioning

confidence: 71%

“…In the recent years, a thorough description of the patterns and hydrodynamic regimes have been reported for systems where gas is injected in a saturated granular medium. For injection at a fixed overpressure and grain compacity in a quasibidimensional (Hele-Shaw) cell, a transition has been reported between the viscous and frictional regimes [39], or between a Saffman-Taylor instability, dense suspension fracturing and fingering in a fixed porous medium [40]. When the compacity is not constrained, and the cell gap varies, more regimes can be found, exhibiting a strong coupling between the fluid and grain flows, as well as an expansion and fluidization of the granular bed [41].…”

Section: Introductionmentioning

confidence: 99%

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Flow and fracture in water-saturated, unconstrained granular beds

et al. 2015

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The injection of gas in a liquid-saturated granular bed gives rise to a wide variety of invasion patterns. Many studies have focused on constrained porous media, in which the grains are fixed in the bed and only the interstitial fluid flows when the gas invades the system. With a free upper boundary, however, the grains can be entrained by the ascending gas or fluid motion, and the competition between the upward motion of grains and sedimentation leads to new patterns. We propose a brief review of the experimental investigation of the dynamics of air rising through a water-saturated, unconstrained granular bed, in both two and three dimensions. After describing the invasion pattern at short and long time, a tentative regime-diagram is proposed. We report original results showing a dependence of the fluidized zone shape, at long times, on the injection flow rate and grain size. A method based on image analysis makes it possible to detect not only the fluidized zone profile in the stationary regime, but also to follow the transient dynamics of its formation. Finally, we describe the degassing dynamics inside the fluidized zone, in the stationary regime. Depending on the experimental conditions, regular bubbling, continuous degassing, intermittent regime or even spontaneous flow-to-fracture transition are observed.

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Section: Discussionmentioning

confidence: 71%

Section: Introductionmentioning

confidence: 99%

Flow and fracture in water-saturated, unconstrained granular beds

et al. 2015

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“…Further, during air injection into liquid saturated granular media and suspensions, the characteristics of emerging patterns and behavior of the media depend on injection rate and the competition between mobilized friction and surface forces [31][32][33][34][35][36][37][38][39][40][41][42][43][44]. For example, one observes flow regimes such as two-phase flow in rigid porous media [40][41][42][43][44], capillary fracturing, stick-slip bubbles, and labyrinth patterns [31][32][33][34][35][36][37][38][39].…”

Section: Introductionmentioning

confidence: 99%

“…For example, one observes flow regimes such as two-phase flow in rigid porous media [40][41][42][43][44], capillary fracturing, stick-slip bubbles, and labyrinth patterns [31][32][33][34][35][36][37][38][39]. In the opposite case, during liquid injection into dry granular media [45], for a given imposed flux, the flow behavior goes from stable invasion toward saturated granular fingers for increasing flow rate and viscosity of the invading fluid.…”

Section: Introductionmentioning

confidence: 99%

Pneumatic fractures in confined granular media

et al. 2017

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We perform experiments where air is injected at a constant overpressure P in , ranging from 5 to 250 kPa, into a dry granular medium confined within a horizontal linear Hele-Shaw cell. The setup allows us to explore compacted configurations by preventing decompaction at the outer boundary, i.e., the cell outlet has a semipermeable filter such that beads are stopped while air can pass. We study the emerging patterns and dynamic growth of channels in the granular media due to fluid flow, by analyzing images captured with a high speed camera (1000 images/s). We identify four qualitatively different flow regimes, depending on the imposed overpressure, ranging from no channel formation for P in below 10 kPa, to large thick channels formed by erosion and fingers merging for high P in around 200 kPa. The flow regimes where channels form are characterized by typical finger thickness, final depth into the medium, and growth dynamics. The shape of the finger tips during growth is studied by looking at the finger width w as function of distance d from the tip. The tip profile is found to follow w(d) ∝ d β , where β = 0.68 is a typical value for all experiments, also over time. This indicates a singularity in the curvaturee., more rounded tips rather than pointy cusps, as they would be for the case β > 1. For increasing P in , the channels generally grow faster and deeper into the medium. We show that the channel length along the flow direction has a linear growth with time initially, followed by a power-law decay of growth velocity with time as the channel approaches its final length. A closer look reveals that the initial growth velocity v 0 is found to scale with injection pressure as v 0 ∝ P 3 2 in , while at a critical time t c there is a cross-over to the behavior v(t) ∝ t −α , where α is close to 2.5 for all experiments. Finally, we explore the fractal dimension of the fully developed patterns. For example, for patterns resulting from intermediate P in around 100-150 kPa, we find that the box-counting dimensions lie within the range D B ∈ [1.53,1.62], similar to viscous fingering fractals in porous media.

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“…In e.g., [26][27][28] it was found that a range of different patterns emerge when air is injected in granular suspensions in thin cells. Invasion patterns such as frictional fingering, viscous fingering, fluidized fronts and stick-slip bubbles were observed depending on bead fraction and injection rate.…”

Section: Introductionmentioning

confidence: 99%

Invasion patterns during two-phase flow in deformable porous media

et al. 2015

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We study the formation of viscous fingering and fracturing patterns that occur when air at constant overpressure invades a circular Hele-Shaw cell containing a liquid-saturated deformable porous medium-i.e., during the flow of two non-miscible fluids in a confined granular medium at high enough rate to deform it. The resulting patterns are characterized in terms of growth rate, average finger thickness as function of radius and time, and fractal properties. Based on experiments with various injection pressures, we identify and compare typical pattern characteristics when there is no deformation, compaction, and/or decompaction of the porous medium. This is achieved by preparing monolayers of glass beads in cells with various boundary conditions, ranging from a rigid disordered porous medium to a deformable granular medium with either a semi-permeable or a free outer boundary. We show that the patterns formed have characteristic features depending on the boundary conditions. For example, the average finger thickness is found to be constant with radius in the non-deformable (ND) system, while in the deformable ones there is a larger initial thickness decreasing to the ND value. Then, depending on whether the outer boundary is semi-permeable or free there is a further decrease or increase in the average finger thickness. When estimated from the flow patterns, the box-counting fractal dimensions are not found to change significantly with boundary conditions, but by using a method to locally estimate fractal dimensions, we see a transition in behavior with radius for patterns in deformable systems; In the deformable system with a free boundary, it seems to be a transition in universality class as the local fractal dimensions decrease toward the outer rim, where fingers are opening up like fractures in a paste.

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Morphodynamics during air injection into a confined granular suspension

Cited by 53 publications

References 42 publications

Flow and fracture in water-saturated, unconstrained granular beds

Flow and fracture in water-saturated, unconstrained granular beds

Pneumatic fractures in confined granular media

Invasion patterns during two-phase flow in deformable porous media

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