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 G1: Instabilities at Soft Interfaces IFocus
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Chair: Camille Duprat, LadHyX, Ecole Polytechnique Room: A105 |
Monday, November 21, 2016 8:00AM - 8:13AM |
G1.00001: Sedimentation of slender elastic filaments in a viscous liquid Veronica Raspa, Anke Lindner, Olivia du Roure, Camille Duprat We explore experimentally the dynamics of slender flexible filaments sedimenting in a viscous fluid at low Reynolds number. The observed deformations and dynamics result from a balance between viscous, elastic and gravitational forces on the slender body and thus are characterized by a dimensionless elasto-gravity number. We present measurements of the filaments stationary shape, velocities and trajectories for different initial conditions and filament characteristics (i.e: density, bending rigidity, size). In particular, we observe bending and reorientation of the filament, and investigate the conditions under which the filament can buckle. The introduction of elasticity broadens the spectrum of accessible sedimentation stationary states, compared to those appearing for their rigid counterparts where nor bending or buckling are allowed. [Preview Abstract] |
Monday, November 21, 2016 8:13AM - 8:26AM |
G1.00002: Viscous fingering in an elastic channel Andrew L. Hazel, Lucie Duclou\'e, Anne Juel We investigate experimentally the fingering instability of a flat, steadily propagating interface in a Hele-Shaw channel, where the top boundary has been replaced by an elastic membrane. In order to create a steadily propagating flat front, we exploit the reopening modes of fluid-filled elasto-rigid channels. The collapsed upper boundary reopens through the steady propagation of a wide finger, when air is injected from one end at a constant flow rate. For high levels of collapse and high finger speed, the tip of the finger becomes flat, creating a leading edge normal to the direction of propagation, which in turn is subject to a smaller scale viscous fingering instability. By modifying the cross-sectional geometry of the channel, we can actuate the finger shape to observe a variety of small-scale fingering phenomena including growth in a direction normal to the propagation and dendrite formation. The instability of the flat front exhibits constant-length fingers, very similar to the stubby fingers observed in radial compliant Hele-Shaw cells, and reminiscent of the printer’s instability travel with the front. We investigate the geometry of those fingers in terms of the speed of the front, and the geometry of the reopening region. [Preview Abstract] |
Monday, November 21, 2016 8:26AM - 8:39AM |
G1.00003: Crustal fingering: solidification on a moving interface Xiaojing Fu, Joaquin Jimenez-Martinez, Mark Porter, Luis Cueto-Felgueroso, Ruben Juanes Viscous fingering--the hydrodynamic instability that takes place when a less viscous fluid displaces a more viscous fluid--is a well known phenomenon. Motivated by the formation of gas hydrates in seafloor sediments and during the ascent of gas bubbles through ocean water, here we study the interplay of immiscible viscous fingering with solidification of the evolving unstable interface. We present experimental observations of the dynamics of a bubble of Xenon in a water-filled and pressurized Hele-Shaw cell. The evolution is controlled by two processes: (1) the formation of a hydrate ``crust" around the bubble, and (2) viscous fingering from bubble expansion. To reproduce the experimental observations, we propose a phase-field model that describes the nucleation and thickening of a porous solid shell on a moving gas-liquid interface. We design the free energy of the three-phase system (gas-liquid-hydrate) to rigorously account for interfacial effects, mutual solubility, and phase transformations (hydrate formation and disappearance). We introduce a pseudo-plasticity model with large variations in viscosity to describe the plate-like rheology of the hydrate shell. We present high-resolution numerical simulations of the model, which illustrate the emergence of complex "crustal fingering" patterns as a result of gas fingering dynamics modulated by hydrate growth at the interface. [Preview Abstract] |
Monday, November 21, 2016 8:39AM - 8:52AM |
G1.00004: Elastic Suppression of Viscous Fingering Gunnar Peng, John Lister Consider peeling an elastic tape or beam away from a rigid base to which it is stuck by a film of viscous liquid. The peeling motion requires air to invade the viscous liquid and is thus susceptible to the Saffman--Taylor fingering instability. We analyse the fundamental travelling-wave solution and show that the advancing air--liquid interface remains linearly stable at higher capillary numbers than in a standard Hele-Shaw cell. A short-wavelength expansion yields an analytical expression for the growth rate which is valid for all unstable modes throughout the parameter space, allowing us to identify and quantify four distinct physical mechanisms that each help suppress the instability. Applying our method to the experiments by Pihler-Puzovic et al. (2012) reveals that the radial geometry and time-variation stabilize the system further. [Preview Abstract] |
Monday, November 21, 2016 8:52AM - 9:05AM |
G1.00005: Viscous fingering of a draining suspension Yun Chen, Frank Malambri, Sungyon Lee The Saffman-Taylor viscous fingering arises when a viscous oil is withdrawn from a Hele-Shaw cell that is filled with a less viscous fluid. When particles are introduced into the draining fluid, new behaviors emerge, which are unobserved in the well-established pure oil case. We experimentally investigate the particle-modified inward fingering for varying particle concentrations. In particular, the fingering growth rate and number of fingers are experimentally quantified and are shown to be directly affected by the presence of particles. The physical mechanism of the particle-modified fingering is also discussed. [Preview Abstract] |
Monday, November 21, 2016 9:05AM - 9:18AM |
G1.00006: Capillary pinch-off of a viscous suspension. Joris Chateau, Elisabeth Guazzelli, Henri Lhuissier We study how the presence of non-Browian, non-colloidal and neutrally buoyant beads suspended in a Newtonian liquid affects the break-up of a capillary thread. Both unstable capillary bridges and threads stretched behind a dripping drop are considered. On the early stage of pinch-off, the suspension behaves as a continuous medium. On the later stage, when the neck diameter reaches a few particle sizes, the pinch-off accelerates continuously until the thinning rate of a pure liquid thread is recovered. We will discuss how these two regimes and their transition depend on the particle volume fraction, size and wettability, as well as on the pinch-off configuration. [Preview Abstract] |
Monday, November 21, 2016 9:18AM - 9:31AM |
G1.00007: The dynamics of semiflexible actin filaments in simple shear flow Yanan LIU, Anke LINDNER, Olivia DU ROURE The rheological properties of complex fluids made of particles in a suspended fluid depend on the behavior of microscopic particles in flow. A first step to understand this link is to investigate the individual particle dynamics in simple shear flows. A rigid rod will perform so-called Jeffery orbits, however when the rod becomes flexible and Brownian, the behavior in terms of deformation and migration is still to be fully understood. We chose here to address this situation by studying experimentally the behavior of semiflexible polymers. We use actin filaments and combine fluorescent labeling techniques, microfluidic devices to carry out controlled systematical experiments. Different dynamics are observed as a function of the elasto-viscous number, comparing viscous forces to elastic restoring forces $\zeta=(8\pi\eta\dot\gamma L^4)/(Lpk_BT)$. The bending modulus of the actin filaments is given by its persistence length $Lp=17\pm1\mu m$. When increasing the elasto-visous number we subsequently observe tumbling, buckling, and bending under flow. Those observations seem to be in good agreement with recent numerical simulations. At the same time, actin filaments fluctuate due to Brownian motion and these fluctuations can modify the individual dynamics of actin filaments. [Preview Abstract] |
Monday, November 21, 2016 9:31AM - 9:44AM |
G1.00008: Swelling-induced surface instabilities in growing poroelastic polymer networks Matthew G. Hennessy, Alessandra Vitale, Joao T. Cabral, Omar K. Matar The swelling that occurs when a deformable polymer network absorbs solvent can generate large compressive stresses which, in turn, can lead to a rich variety of surface instabilities. In this talk, we will discuss recent experiments by our group which suggest that the growth of a polymer network by photopolymerisation and the onset of swelling-induced surface instabilities can simultaneously occur and drive the self-assembly of complex three-dimensional structures. In addition, we will present a theoretical model of photopolymersation that captures the growth, swelling, and mechanical response of the polymer network. The model is based on an Eulerian formulation of nonlinear poroelasticity. The transport of monomer is described by a generalisation of Darcy's law that accounts for flow due to gradients in the pressure and composition. A combination of asymptotic analysis and finite-element simulations is used to explore the coupling between growth and instability as well as the resulting surface morphologies. [Preview Abstract] |
Monday, November 21, 2016 9:44AM - 9:57AM |
G1.00009: Patterns in swelling hydrogels Chris MacMinn, Thibault Bertrand, Jorge Peixinho, Shomeek Mukhopadhyay Swelling is a process in which a porous material spontaneously grows by absorbing additional pore fluid. Polymeric hydrogels are highly deformable materials that can experience very large volume changes during swelling. This allows a small amount of dry gel to absorb a large amount of fluid, making gels extremely useful in applications from moisture control to drug delivery. However, a well-known consequence of these extreme volume changes is the emergence of a striking morphological instability. We study the transient mechanics of this instability here by combining a theoretical model with a series of simple experiments, focusing on the extent to which this instability can be controlled by manipulating the rate of swelling. [Preview Abstract] |
Monday, November 21, 2016 9:57AM - 10:10AM |
G1.00010: Lubricated wrinkles Ousmane Kodio, Ian Griffiths, Dominic Vella We investigate the problem of an elastic beam above a thin viscous layer. The beam is subject to a fixed end-to-end displacement, which will ultimately cause it to adopt the Euler-buckled state. However, additional liquid must be drawn in to allow this buckling. In the interim, the beam forms a wrinkled state with wrinkles coarsening over time. This problem has been studied experimentally by Vandeparre \textit{et al.~Soft Matter} (2010), who provided a scaling argument suggesting that the wavelength, $\lambda$, of the wrinkles grows according to $\lambda\sim t^{1/6}$. However, a more detailed theoretical analysis shows that, in fact, $\lambda\sim(t/\log t)^{1/6}$. We present numerical results to confirm this and show that this result provides a better account of previous experiments. [Preview Abstract] |
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