Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session H1: Instabilities at Soft Interfaces IIFocus
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Chair: Chris MacMinn, Department of Engineering Science, University of Oxford Room: A105 |
Monday, November 21, 2016 10:40AM - 10:53AM |
H1.00001: Bubbles Rising Through a Soft Granular Material Robin Le Mestre, Chris MacMinn, Sungyon Lee Bubble migration through a soft granular material involves a strong coupling between the bubble dynamics and the deformation of the material. This is relevant to a variety of natural processes such as gas venting from sediments and gas exsolution from magma. Here, we study this process experimentally by injecting air bubbles into a quasi-2D packing of soft hydrogel beads and measuring the size, speed, and morphology of the bubbles as they rise due to buoyancy. Whereas previous work has focused on deformation resisted by intergranular friction, we focus on the previously inaccessible regime of deformation resisted by elasticity. At low confining stress, the bubbles are irregular and rounded, migrating via local rearrangement. At high confining stress, the bubbles become unstable and branched, migrating via pathway opening. [Preview Abstract] |
Monday, November 21, 2016 10:53AM - 11:06AM |
H1.00002: Dynamic of particle-laden liquid sheet Alban Sauret, Pierre Jop, Anthony Troger Many industrial processes, such as surface coating or liquid transport in tubes, involve liquid sheets or thin liquid films of suspensions. In these situations, the thickness of the liquid film becomes comparable to the particle size, which leads to unexpected dynamics. In addition, the classical constitutive rheological law cannot be applied as the continuum approximation is no longer valid. Here, we consider experimentally a transient free liquid sheet that expands radially. We characterize the influence of the particles on the shape of the liquid film as a function of time and the atomization process. We highlight that the presence of particles modifies the thickness and the stability of the liquid sheet. Our study suggests that the influence of particles through capillary effects can modify significantly the dynamics of processes that involve suspensions and particles confined in liquid films. [Preview Abstract] |
Monday, November 21, 2016 11:06AM - 11:19AM |
H1.00003: Flow-induced compaction of soft poroelastic materials Japinder S. Nijjer, Duncan R. Hewitt, M. Grae Worster, Jerome A. Neufeld Fluid flows through poroelastic materials can result in solid deformation driven by the distribution of viscous shear stresses. The porosity and permeability of the solid matrix is altered spatially through a non-trivial coupling to the fluid flow. This behaviour is studied experimentally by examining fluid flow through a packing of soft hydrogel spheres driven by an imposed pressure head. The pressure head is varied, and, for each pressure, the steady-state mass flux and solid deformation are measured. For large pressure gradients, the fluid flow is found to decrease the permeability in such a way as to produce a flux that is independent of the applied pressure gradient. Measurements of the internal deformation, obtained by particle tracking, show that the medium compacts non-uniformly, with the porosity being lower at the outlet compared to the inlet. Intriguingly, we find a reproducible hysteresis of the poroelastic deformation between increasing and decreasing increments of the applied pressure head. The experimental results are compared to a simple one-dimensional model that accounts for non-linear elasticity of the solid and non-constant permeability. [Preview Abstract] |
Monday, November 21, 2016 11:19AM - 11:32AM |
H1.00004: Droplets sliding down inclined planes: unexpected dynamics on elastomer plates Aurelie Hourlier-Fargette, Arnaud Antkowiak, Sebastien Neukirch Droplet dynamics on an angled surface results from a competition between the weight of the droplet, capillary forces, and viscous dissipation inside the drop. The motion of droplets on stiff surfaces has been investigated for a long time, both experimentally and theoretically, while recent studies have shown the interesting physics underlying the sliding of droplets on soft surfaces. We focus on the dynamics of water-glycerol mixture droplets sliding down vertical plates of silicone elastomers, highlighting an unexpected behavior: the droplet dynamics on such a surface includes two regimes with different constant speeds. These results contrast with those found in the literature for droplets sliding on materials such as treated glass. We investigate the universality of this behavior on various elastomers, and study in detail the two regimes and the sharp transition observed between them. Different candidates can be responsible for the sudden speed change: bistability, chemical interaction with the substrate, softness of the material, etc. Our experiments to clarify the role of each of them reveal an unexpected link between microscopic phenomena at the scale of the polymer matrix and the macroscopic dynamics of a droplet. [Preview Abstract] |
Monday, November 21, 2016 11:32AM - 11:45AM |
H1.00005: Formation and destabilization of the particle band on the fluid-fluid interface Jungchul Kim, Feng Xu, Sungyon Lee An inclusion of spherical particles in a viscous fluid can fundamentally change the interfacial dynamics and even cause interfacial instabilities. For instance, particle-induced viscous fingering has been previously observed even in the absence of the destabilizing viscosity ratio, when particles are added to the viscous invading fluid inside a Hele-Shaw cell. In the same flow configuration, the effects of channel confinement lead to the appearance of a novel fingering regime which consists of the formation and break-up of a dense particle band on the interface. In this talk, we experimentally characterize the evolution of the fluid-fluid interface in this new physical regime and propose a simple model of the particle band that successfully captures the onset of fingering as a function of the particle concentrations and particle size. [Preview Abstract] |
Monday, November 21, 2016 11:45AM - 11:58AM |
H1.00006: Influence of surface tension on the instabilities and bifurcations of a particle in a drop under shear Francois Gallaire, Lailai Zhu While the deformation regimes under flow of anuclear cells, like red blood cells, have been widely analyzed, the dynamics of nuclear cells are less explored. The objective of this work is to investigate the interplay between the stiff nucleus, modeled here as a rigid spherical particle and the surrounding deformable cell membrane, modeled for simplicity as an immiscible droplet, subjected to an external unbounded plane shear flow. A three-dimensional boundary integral implementation is developed to describe the interface-structure interaction characterized by two dimensionless numbers: the capillary number $Ca$, defined as the ratio of shear to capillary forces and and the particle-droplet size ratio. For large $Ca$, i.e. very deformable droplets, the particle has a stable equilibrium position at the center of the droplet. However, for smaller $Ca$, both the plane symmetry and the time invariance are broken and the particle migrates to a closed orbit located off the symmetry plane, reaching a limit cycle. For even smaller capillary numbers, the time invariance is restored and the particle reaches a steady equilibrium position off the symmetry plane. This series of bifurcations is analyzed and possible physical mechanisms from which they originate are discussed. [Preview Abstract] |
Monday, November 21, 2016 11:58AM - 12:11PM |
H1.00007: Soft Plumbing: Direct-Writing and Controllable Perfusion of Tubular Soft Materials Axel Guenther, Patricia Omoruwa, Haotian Chen, Arianna McAllister, Mark Jeronimo, Shashi Malladi, Navid Hakimi, Li Cao, Arun Ramchandran Tubular and ductular structures are abundant in tissues in a wide variety of diameters, wall thicknesses, and compositions. In spite of their relevance to engineered tissues, organs-on-chips and soft robotics, the rapid and consistent preparation of tubular structures remains a challenge. Here, we use a microfabricated printhead to direct-write biopolymeric tubes with dimensional and compositional control. A biopolymer solution is introduced to the center layer of the printhead, and the confining fluids to the top and the bottom layers. The radially flowing biopolymer solution is sandwiched between confining solutions that initiate gelation, initially assuming the shape of a funnel until emerging through a cylindrical confinement as a continuous biopolymer tube. Tubular constructs of sodium alginate and collagen~I were obtained with inner diameters (0.6-2.2mm) and wall thicknesses (0.1-0.4mm) in favorable agreement with predictions of analytical models. We obtained homogeneous tubes with smooth and buckled walls and heterotypic constructs that possessed compositions that vary along the tube circumference or radius. Ductular soft materials were reversibly hosted in 3D printed fluidic devices for the perfusion at well-defined transmural pressures to explore the rich variety of dynamical features associated with collapsible tubes that include buckling, complete collapse, and self-oscillation [Preview Abstract] |
Monday, November 21, 2016 12:11PM - 12:24PM |
H1.00008: Fracture Phenomena in Foams: From Film Instability to Wave Propagation Sascha Hilgenfeldt, Peter Stewart Injection of a gas into a gas/liquid foam is known to give rise to instability phenomena on a variety of time and length scales. Macroscopically, one observes a propagating gas-filled structure that can display properties of liquid finger propagation as well as of fracture in solids. The observation of both large-scale, finger-like cracks (without film breakage) and brittle cleavage phenomena (consisting of successive film ruptures) is explained through careful modeling of phenomena ranging from thin-film instabilities to friction between bubbles and confining plates. Whereas we use a network approach with full representation of the foam microstructure to model the cracks, we also derive a continuum limit description in order to investigate possible modes of wave propagation and their feedback on the fracture process. [Preview Abstract] |
Monday, November 21, 2016 12:24PM - 12:37PM |
H1.00009: Instability in poroelastic media Satyajit Pramanik, John Wettlaufer Fluid flow in deformable porous materials, which play significant role in different biological and geological systems of wide range of scales, is a highly nonlinear problem. Feedback from the elastic deformation of the solid skeleton on the fluid flow and vice-versa gives rise to pattern formation in the porosity structure of the skeleton [1]. We view some of these patterns as instabilities of the coupled fluid-solid system. Due to highly nonlinear nature of the problem, very little has been understood about this instability. Here, we use a minimal poroelastic theory to understand the pattern formation in a fluid-saturated poroelastic material and discuss the similarities/differences with viscous fingering in non-deformable porous media.\newline $[1]$ C. M. MacMinn, E. R. Dufresne, and J. Wettlaufer, ``Fluid-driven deformation of a soft granular material," Phys. Rev. X 5, 011020 (2015). [Preview Abstract] |
Monday, November 21, 2016 12:37PM - 12:50PM |
H1.00010: Elasticity-Driven Backflow of Fluid-Driven Cracks Ching-Yao Lai, Emilie Dressaire, Guy Ramon, Herbert Huppert, Howard A. Stone Fluid-driven cracks are generated by the injection of pressurized fluid into an elastic medium. Once the injection pressure is released, the crack closes up due to elasticity and the fluid in the crack drains out of the crack through an outlet, which we refer to as backflow. We experimentally study the effects of crack size, elasticity of the matrix, and fluid viscosity on the backflow dynamics. During backflow, the volume of liquid remaining in the crack as a function of time exhibits a transition from a fast decay at early times to a power law behavior at late times. Our results at late times can be explained by scaling arguments balancing elastic and viscous stresses in the crack. This work may relate to the environmental issue of flowback in hydraulic fracturing. [Preview Abstract] |
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