Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session B04: Suspensions: General II |
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Chair: Sungyon Lee, University of Minnesota Room: 203 |
Saturday, November 23, 2019 4:40PM - 4:53PM |
B04.00001: Shear-induced migration of a suspension under planar confinement Fernando Vereda, Nikolay Ionkin, Amanda A. Howard, Martin Maxey, Daniel Harris The oscillatory flow of a suspension of neutrally buoyant, non-Brownian spherical particles in a rectangular channel at low Reynolds number is studied through experiments and numerical simulations. Particles, which are practically confined to a plane, migrate to regions of lower shear rate. Prior experimental and numerical work in oscillating Poiseuille flows has demonstrated the importance of the strain amplitude on shear-induced migration. In this talk, we present results for the early development of the suspension, including the dependence of the steady state configuration of the system and the dynamics of the shear-induced migration on particle concentration, strain amplitude, and channel dimensions. Our measurements are directly compared to simulations using the Force Coupling Method (FCM) for monodispersed spherical particles in a channel. [Preview Abstract] |
Saturday, November 23, 2019 4:53PM - 5:06PM |
B04.00002: Self-similarity in particle accumulation at fluid-fluid interface Li Wang, Yun Chen, Rui Luo, Sungyon Lee When the mixture of viscous oil and non-colloidal particles displace air between two parallel plates, the coupled effects of shear-induced migration of particles and the secondary flow near the interface lead to the gradual accumulation of particles on the advancing oil-air interface. This particle accumulation results in the fingering of an otherwise stable fluid-fluid interface. While the previous works by Xu and colleagues have focused on the resultant instability, one unexplored yet striking feature of the experiments is the self-similarity in the concentration profile of the accumulating particles. In this talk, we model the system mathematically by considering the depth-averaged particle transport equation and suspension balance model. To capture the physical effect of the particle accumulation, we extract the particle flux as a function of local particle concentration from the experiments and include the secondary flow effect in the transport equation. The numerical results of depth-averaged particle concentration profile are presented and compared with the experiments. [Preview Abstract] |
Saturday, November 23, 2019 5:06PM - 5:19PM |
B04.00003: Surface instability of shear-thickening suspensions down an inclined plane Baptiste Darbois Texier, Bloen Metzger, Henri Lhuissier, Yoel Forterre Shear-thickening of dense suspensions is one of the most appealing phenomena of science festivals. The dramatic increase of the viscosity with the shear stress is now understood as a frictional transition occurring above a critical stress set by a repulsive interaction between particles. Here, we investigate the stability of a thin film of cornstarch suspension flowing down an inclined plane. At low packing fractions, the film is unstable above a critical Reynolds number given by the well-known Kapitza criterium for Newtonian fluids. However, at high packing fractions, as shear-thickening becomes discontinuous, a new instability emerges at Reynolds numbers much smaller than the Kapitza threshold. We show that this instability arises from the characteristic S-shape of the rheological law. [Preview Abstract] |
Saturday, November 23, 2019 5:19PM - 5:32PM |
B04.00004: Particle-induced miscible fingering Rui Luo, Yun Chen, Sungyon Lee We experimentally inject silicone oil into the mixture of oil and non-colloidal particles inside a Hele-Shaw cell, to investigate the connection between miscible fingering and the flow structure that develops in the thin gap. Previous studies with pure fluids have demonstrated that the onset of miscible fingering coincides with the transition from a smooth tongue-like structure to a sharp front between invading and defending fluids inside the thin gap. Our current experiments with suspensions reveal the same general behavior at the onset of miscible fingering, which we capture qualitatively using a continuum model. However, beyond the onset, we observe distinctly different morphologies of miscible fingering, which depend on the ratio of the gap thickness to particle diameter. We present the new quantitative measurements that highlight these differences and discuss how the wall confinement may alter the particle dynamics and the resultant fingering patterns. [Preview Abstract] |
Saturday, November 23, 2019 5:32PM - 5:45PM |
B04.00005: Experimental and numerical studies of particle-laden fluid flows over a porous media model Eileen Haffner, Changwoo Kang, Nina Shapley, Parisa Mirbod Suspension flows has been extensively studied through various experimental techniques and numerical simulations but only in smooth channels. On the other hand, flow of pure Newtonian fluid over porous media has been the topic of several investigations. However, to the best of the author's knowledge, how these two engineering systems relate to one another is still unknown. This study was conducted to examine the interaction between various suspensions over a porous media model. Two experimental techniques were utilized, particle image velocimetry (PIV) and nuclear magnetic resonance (NMR) imaging. The PIV data provided two dimensional velocity vector fields which was used to extract slip velocity and shear rate at the interface between the free flow region and the porous media for dilute suspension flows. The NMR measurements provided three-dimensional velocity and concentration information through and above the porous media for higher concentrated suspensions. It was found that the slip velocity, shear rate, and concentration profiles are strongly dependent on the suspension concentrations as well as the geometry and properties of the porous media. Theoretical simulations were developed and compared to the experimental results, showing good agreement in the free flow region. [Preview Abstract] |
Saturday, November 23, 2019 5:45PM - 5:58PM |
B04.00006: Hysteresis in viscous suspensions Hugo Perrin, Cecile Clavaud, Bloen Metzger, Matthieu Wyart, Yoel Forterre Hysteresis is a major feature of the solid-liquid transition in granular materials. This property, by allowing metastable states, can potentially yield catastrophic phenomena such as landslides. The origin of hysteresis in granular flows is still debated. However, most mechanisms put forward so far rely on inertia at the particle level. Here, we study the avalanche dynamics of non-Brownian suspensions in slowly rotating drums and reveal large hysteresis of the avalanche angle even without inertia. By using microsilica particles whose interparticle friction can be turned off, we show that microscopic friction, conversely to inertia, is key to triggering hysteresis. To understand this link between friction and hysteresis, we measured the suspension rheology close to the flow onset for frictional and frictionless suspensions. We show that the flow rule for frictionless particles is monotonous with a power law of exponent $0.37\pm0.05$, in close agreement with the previous theoretical prediction, $0.35$. By contrast, the flow rule for frictional particles suggests a velocity-weakening behavior. These findings show that hysteresis can occur in particulate media without inertia, and by highlighting the role of microscopic friction, it questions the intimate nature of this phenomenon. [Preview Abstract] |
Saturday, November 23, 2019 5:58PM - 6:11PM |
B04.00007: Mixing in sheared suspensions Regis Turuban, Henri Lhuissier, Bloen metzger Mixing occurs spontaneously in sheared suspensions even at low Reynolds number. The presence of particles induces disorder which lead to exponential elongations within the fluid: concentration levels thus quickly spread and decay. We experimentally characterize the evolution of the concentration PDFs of a blob of fluorescent dye initially injected in an index-matched suspension. High precision optical imaging technics reveal for the first time the finnest spatial details of the concentration field possibly generated by this chaotic flow (Batchelor scales). We find that at short times, the evolution of the concentration PDFs are correctly predicted by a model based solely on the stretching kinematics. At longer times, we show that to predict the experimental observations, the model should also include the effect of coalescence between adjacent lamellae of dye. [Preview Abstract] |
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