Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session D2: Suspensions: Migration and Mixing |
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Chair: Roger Bonnecaze, University of Texas at Austin Room: 101 |
Sunday, November 22, 2015 2:10PM - 2:23PM |
D2.00001: How to Magnetically Generate Flows in Dead-Ends with Dilute Suspensions of Iron Particles Roger Bonnecaze, Michael Clements Dilute suspensions of iron particles in the presence of a magnetic field can create flows in dead-ends of pores, channels and even blocked arteries to help dissolve clots. Observations show that added iron particles in a rotating magnetic field form rotating rods along the wall of the blocked channel, creating a convective flow. We present a proposed mechanism for this magnetically driven flow in the form of coupled particle-scale and channel-scale flow models. At the particle-scale, particles chain up to lengths balancing magnetic and hydrodynamic forces on the resulting rods. The weak gradient of the magnetic field causes the rods to accumulate on one side of the channel. The rods rotate due to the rotating magnetic field, provided the field strength is high enough, which creates a localized body couple in the flow that drives a macroscopic convective flow in the channel. Coupled transport equations for the particles and the suspension as a whole are presented. The model equations are solved asymptotically and numerically and compared to experimental observations. Design rules for implementation of this technique are presented to optimize the flow. [Preview Abstract] |
Sunday, November 22, 2015 2:23PM - 2:36PM |
D2.00002: Three-dimensional collision of general-shaped particles in a viscous fluid Mohsen Daghooghi, Iman Borazjani The hydrodynamic interactions between rigid particles in a viscous fluid in semi-dilute and dense suspensions require a collision strategy to detect and prevent near collision and overlapping between particles in numerical simulations. While various collision models have been developed for spherical particles, very limited models are currently available for complex-shaped particles. In earlier methods, a repulsive force is applied to the particles when their distance is less than a threshold value and, depending on the magnitude of this repulsive force, collision may not be prevented or particles may bounce unrealistically. We have developed a three-dimensional numerical technique for general-shaped particles that: (1) detects near collision of complex-shaped objects in contrast to straightforward detection of spherical particles; and (2) guaranties overlap prevention. Contrary to conventional methods, we used an iterative method to exert a sufficient force and/or moment on each particle to prevent particles from overlapping without causing them to bounce back as expected at low Stokes numbers. [Preview Abstract] |
Sunday, November 22, 2015 2:36PM - 2:49PM |
D2.00003: Transport of particle-laden viscoelastic suspensions: tuning particle behavior with elasticity and geometry Alexander Barbati, Agathe Robisson, Elizabeth Dussan V., Gareth McKinley The transport of particle-laden viscoelastic suspensions is routine in several industrial and natural systems. Many applications, such as hydraulic fracturing in the oilfield, require the successive (and occasionally simultaneous) flow and placement or rigid particles, commonly known as proppant. Hydraulically-generated fractures are routinely less than 6 particle diameters in width. We investigate the flow of viscoelastic particle-laden suspensions in microfabricated geometries mimicking hydraulically-generated fractures under a variety of dynamic conditions to illustrate the interaction between inertia, elasticity, and geometry on particle behavior during flow. We characterize the flow in these model geometries with a combination of streakline imaging, particle image velocimetry, and direct imaging of model proppant particles embedded in the flow. We accompany these small-scale measurements with macro-scale interrogation of fluid rheology by measuring material functions of the working fluid in under shear and extension. These material functions are used in concert with imposed flow conditions and imaging results to identify dominant transport mechanisms on the channel and particle scale, which indicate overall system behavior. [Preview Abstract] |
Sunday, November 22, 2015 2:49PM - 3:02PM |
D2.00004: Viscous resuspension in pressure driven confined flows of suspensions Anaïs Machado, Hugues Bodiguel, Annie Colin Flows of non-Brownian semi-dilute suspensions are mainly governed by the spatial repartition of the particles. At low Reynolds numbers, it is indeed generally non-uniform due to the cross-stream migration towards low sheared regions of the flow. Though this phenomenon has been has been the focus of many work for several decades, discrepancies still exists between experiments and modelling, and in particular for pressure driven confined flows which are the focus of this work. In order to quantify shear induced migration, we take advantage horizontal flow of buoyant particles in slits, where viscous resuspension is balanced by buoyancy. We study PMMA rigid spheres of 6~$\mu$m dispersed several liquids of various density, and impose pressure driven flows in slits of several tens of $\mu$m. Using advanced particle imaging velocimetry techniques and confocal microscopy, we measure systematically both volume fraction and velocity profiles. At low flow rates, the particle density is highly asymmetric due to buoyancy whereas it becomes symmetric at high flow rate, due to shear-induced migration. The transition occurs for a given Shields number which we characterize as a function of concentration and confinement. The results are analyzed and discussed in the framework. [Preview Abstract] |
Sunday, November 22, 2015 3:02PM - 3:15PM |
D2.00005: Particle dispersion in non-stationary and non-uniform suspension flows Amanda Howard, Martin Maxey, Kyongmin Yeo In a low Reynolds number pressure driven flow of neutrally buoyant, non-Brownian particles in suspension there is usually an irreversible dispersion of the particles and a net flux towards the central core resulting in a region of high concentration there and low concentration near the walls. Surface roughness and the resulting near-contact forces between particles have been shown to the leading source of irreversibility in suspension shear flows. We report on a series of numerical simulations of particle suspensions in a planar channel for developing flows under both steady and oscillating pressure gradients and for different non-uniform particle distributions. We observe a correlation between the particle pressure associated with contact forces and the development of particle fluxes. In low shear zones, there may be a high number of near-contacts or high coordination number but limited particle pressure. We relate the results to our recent study of suspension plugs where there is a sharp change in particle concentration across a front in the streamwise direction and in oscillatory flow gives a local flux towards the walls. We consider the results in the context of stress balance models and mechanisms generating net particle transport. [Preview Abstract] |
Sunday, November 22, 2015 3:15PM - 3:28PM |
D2.00006: Radial distribution of neutrally buoyant spherical particles suspended in Poiseuille flow Yusuke Morita, Tomoaki Itano, Masako Sugihara-Seki An experimental study of the inertial migration of neutrally buoyant spherical particles suspended in the Poiseuille flow through circular tubes has been conducted at Reynolds numbers (Re) from 100 to 1000. The distributions of particles at downstream cross-sections were measured and the probability density function (PDF) of particles was calculated as a function of the radial position. At relatively high Re, the PDF was found to have two peaks, corresponding to the so-called Segre-Silberberg annulus and the inner annulus, whereas at low Re only the Segre-Silberberg annulus was present. As the measurement sites got downstream, the fraction of the particles observed on the inner annulus decreased and its radial position moved outward towards the Segre-Silberberg annulus. These results suggest that, if the tubes were long enough, the inner annulus would disappear, so that only the Segre-Silberberg annulus would be present. [Preview Abstract] |
Sunday, November 22, 2015 3:28PM - 3:41PM |
D2.00007: The motion of a light particle in a rotating Stokes flow Tom Mullin, Tania Sauma Perez, Yang Li We present the results of experimental investigations into the motion of light spheres in a rotating horizontal drum filled with viscous fluid. Stokesian dynamics calculations indicate a single stable fixed point on the centreline of the flow whereas calculations with finite sized spheres suggest the possibility of a range of fixed points. Our results support the latter with good quantitative accord between theory and experiment. We also consider the effects of roughness, porosity and elasticity on the fixed points and dynamics. [Preview Abstract] |
Sunday, November 22, 2015 3:41PM - 3:54PM |
D2.00008: Mixing in sheared suspensions Mathieu Souzy, Nora Cherifa Abid, Emmanuel Villermaux, Bloen Metzger Mixing occurs spontaneously in sheared suspensions, even at low Reynolds number. Under flow, successive collisions between particles deviate the laminar streamlines, and thus induce disturbances in the fluid phase, which produce very efficient mixing. We measure fluid velocity fields by performing high spatial resolution PIV experiments within a sheared suspension, and we numerically advect isolated scalar filaments in the flow using Diffusive Strip Method. Stretching law parameters are measured from the elongation of the filaments, and are used to fully characterize the process. The deformation statistics are found to be well modeled by a Langevin equation with multiplicative noise, which can be coupled with diffusion to infer the probability density function of the concentration in the medium. [Preview Abstract] |
Sunday, November 22, 2015 3:54PM - 4:07PM |
D2.00009: Suspension Dynamics of Liquefied Lignocellulosic Biomass in Pipeflow using Echo Particle Image Velocimetry Nicholas DeMarchi, Christopher White Echo particle image velocimetry (EPIV) is used to acquire planar fields of velocity in pipeflow of liquefied biomass. The biomass used is acid washed corn stover liquefied by enzymatic hydrolysis. The liquefaction process produces a complex multiphase fluid suspension with a microstructure consisting of insoluble solid particles dispersed within a continuous liquid phase. The solid particles are generally heavier than the liquid phase, non-spherical, and distributed over a wide range of aspect ratios and sizes. Batches of liquefied biomass are produced at incremental mass loadings doubling from 1.5\% to 12\%. The rheology, microstructure, and solid particle settling velocities of the liquefied biomass as a function of mass loading is first quantified. Next, EPIV is used to measure and quantify the flow dynamics of liquefied biomass suspensions under laminar pressure driven pipeflow conditions. Finally, Information gathered from the experimental data is used to simulate particle settling rates and predict the particle physics under the same pipeflow conditions.? [Preview Abstract] |
Sunday, November 22, 2015 4:07PM - 4:20PM |
D2.00010: Flow of a suspension over an obstacle: revisiting an old problem in a new context Jeffrey Morris, Hamed Haddadi, Shahab Shojaei-Zadeh, Kevin Connington The flow of a fluid over an obstacle, with the associated separation of streamlines and recirculating wake, is a classical fluid mechanical phenomena that has been instrumental in development of our understanding of the interaction of viscous and inertial effects in simple fluids. Visualizations of these behaviors serve as benchmark observations. However, replacing the pure fluid with even a simple multiphase material, a suspension immersed in a Newtonian fluid, poses new questions in understanding the physics in these phenomena. In experimental observation of a dilute suspension flow over bluff bodies in a microfluidic device, we have observed formation of a depleted zone in the recirculating wake region. Using numerical simulations, it has been deduced that rigid spherical particles with finite size released inside the wake region migrate towards the wake boundaries, forming a limit cycle. The tendency of particles to outward motion leads to formation of the depleted region. In the present work, we probe the limit cycle phenomena and other aspects of the suspension flow over obstacles, such as average particle velocities and velocity fluctuations and force on the obstacle using detailed lattice-Boltzmann simulations and microfluidic experiments. [Preview Abstract] |
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