Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session K53: Granular and Multiphase Flows |
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Sponsoring Units: DFD GSOFT GSNP Room: Hilton Baltimore Holiday Ballroom 4 |
Wednesday, March 16, 2016 8:00AM - 8:12AM |
K53.00001: Ferrofluid-based Diamagnetic Particle Separation in U-shaped Microchannels. Yilong Zhou, Xiangchun Xuan We demonstrate in this talk a continuous-flow sheath-free separation method of diamagnetic particles in ferrofluids through U-shaped microchannels. Due to the action of a size-dependent magnetic force, diamagnetic particles are focused into a single stream in the inlet branch of the U-turn and then continuously separated into two streams in its outlet branch. We also develop a 3D numerical model to predict and understand the diamagnetic particle transport during the separation process. The numerical predictions are found to agree well with the experimental observations in a systematic study of multiple parameter effects including ferrofluid flow rate, concentration and magnet-channel distance. [Preview Abstract] |
Wednesday, March 16, 2016 8:12AM - 8:24AM |
K53.00002: Smart microgels for controlling two-phase fluid structure in porous media Jing Fan, David Weitz Understanding the transport of microgels in porous media directly benefits the conformance improvement technique using preformed gels in the oil industry. We develop a new type of microgels that can swell in response to specific stimuli in an aqueous environment. From a practical point of view, this enables us to deliver the microgels to the deep reservoir formation and control the permeability profile more effectively. With confocal microscopy imaging, we show that we can deliver such smart microgels to the high-permeability region in a stratified porous medium, which subsequently changes the two-phase fluid structure in the medium. From a scientific point of view, this allows for characterizing the permeability change due to homogeneous pore-clogging by soft particles instead of surface clogging; using the typical microgels this can hardly be done because we cannot place gel particles with comparable size to the pore uniformly into a porous medium. This study may shed light on understanding many other processes involving the transport of soft particles in porous structures. [Preview Abstract] |
Wednesday, March 16, 2016 8:24AM - 8:36AM |
K53.00003: Effect of Microstructural Geometry for Computing Closure Models in Multiscale Modeling of Shocked Particle Laden Flow Oishik Sen, H.S. Udaykumar, Gustaaf Jacobs Interaction of a shock wave with dust particles is a complex physical phenomenon. A computational model for studying this two-phase system is the Particle-Source in Cell (PSIC) approach. In this method, the dust particles are tracked as point particles in a Lagrangian frame of reference immersed in a compressible fluid. Two-way interaction between the carrier and the dispersed phases is ensured by coupling the momentum and energy transfer between the two phases as source terms in the respective governing equations. These source terms (e.g. drag force on particles) may be computed from resolved numerical simulations by treating each macroscopic point particle as an ensemble of cylinders immersed in a compressed fluid. However the drag so computed must be independent of the geometry of the mesoscale. In this work, the effect of the stochasticity of the microstructural geometry in construction of drag laws from resolved mesoscale computations is studied. Several different arrangement of cylinders are considered and the mean drag law as a function of Mach Number and Volume Fraction for each arrangement is computed using the Dynamic Kriging Method. The uncertainty in the drag forces arising because of the arrangement of the cylinders for a given volume fraction is quantified as 90{\%} credible sets and the effect of the uncertainty on PSIC computations is studied. [Preview Abstract] |
Wednesday, March 16, 2016 8:36AM - 8:48AM |
K53.00004: Time dependent behavior of impact angle in turbulkent pipe flows experience erosion. Amador Guzman, Diego Oyarzun, Magdalena Walczak, Javiera Aguirre Erosion-corrosion in pipe systems transporting slurry turbulent flows is of a great importance in industrial and mining applications, where large volumes of suspended solids are sent up to hundreds of kilometers, to be further processed. The slurry is typically sent over large diameter steel pipes, which not always have an anti-abrasion coating. During the transport, the thickness of the pipe diminishes and eventually leaks and breaks, due to the combined effects of wear and corrosion. The processes of pipe degradation are further enhanced by the content of the slurry electrolytes that might switch from neutral to aggressive. The understanding of these processes in terms of operational parameters is critical for anticipating and mitigating a catastrophic outcome. This paper describes turbulent flow numerical simulations in a slurry transporting steel pipe with an emphasis on the correlation between the time dependent impact angle in the vicinity of the steel pipe and the rate of material loss. Full numerical simulations in a 3D long domain by using an Eulerian --Eulerian two phase flow approach coupled to a $\kappa $-epsilon turbulent model are performed for different solid particle concentration and flow velocity and compared to existing experimental and numerical results for validation with and without gravity. Time-dependent axisymmetric turbulent flow simulations are performed for determining both the time dependent behavior of the axial and radial velocities near the pipe wall and the impact angle. [Preview Abstract] |
(Author Not Attending)
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K53.00005: Caustics and the growth of droplets Rama Govindarajan, S Ravichandran, Samriddhi Ray, P Deepu Caustics are formed when inertial particles of very different velocities collide in a flow, and are a consequence of the dissipative nature of particle motion in a suspension. Using a model vortex-dominated flow with heavy droplets in a saturated environment, we suggest that sling caustics form only within a neighbourhood around a vortex, the square of whose radius is proportional to the product of circulation and particle inertia. Droplets starting close to this critical radius congregate very close together, resulting in large spikes in (Lagrangian) number density. Allowing for merger when droplets collide, we show that droplets starting out close to the critical radius display a much more rapid growth in size than those starting elsewhere, and a large fraction of the large droplets are those that originate within the caustics-forming region. We test these predictions in a two-dimensional simulation of turbulent flow. We hope that our study will be of interest in long-standing problems of physical interest such as the mechanism of broadening of droplet spectra in a turbulent flow. [Preview Abstract] |
Wednesday, March 16, 2016 9:00AM - 9:12AM |
K53.00006: Soft Sphere Suspensions: Flow and Relaxation Marcel Workamp, Joshua A. Dijksman We experimentally study the role of particle elasticity on the rheology of soft sphere suspensions. Experiments consist of custom designed particles with tuneable stiffness. These particles allow us to probe the role of elastic timescales, relaxation and anisotropy in a custom 3D printed shear cell. We find robust rheological features, such as a flow instability, that are not well captured by existing models for suspension flows. In addition, we find relaxation effects after shear even in the absence of shear or thermal fluctuations. We aim to integrate these findings in the emerging unified framework for structured fluids. [Preview Abstract] |
Wednesday, March 16, 2016 9:12AM - 9:24AM |
K53.00007: Impact cratering on granular beds: From the impact of raindrops to the strike of hailstones Leonardo Gordillo, Junping Wang, Fred Japardi, Warren Teddy, Ming Gao, Xiang Cheng Impact craters generated by the impact of a spherical object onto a granular bed strongly depend on the material properties of impactors. As an example, impact cratering by liquid drops and by solid spheres exhibits qualitatively different power-law scalings for the size of resulting impact craters. While the basic energy conservation and dimensional analysis provide simple guiding rules, the detailed dynamics governing the relation between these power-law scalings is still far from clear. To analyze the transition between liquid-drop and solid-sphere impact cratering, we investigate impact cratering by liquid drops for a wide range of viscosities over 7 decades. Using high-speed photography and laser profilometry, we delineate the liquid-to-solid transition and show the emergence of the two asymptotic behaviors and their respective power laws. We find that granular avalanches triggered by impacts are crucial in understanding the energy partition between impacted surfaces and impactors, which directly determines the observed scaling relations. A simple model is constructed for the initial stage of the impact that explains the energy partition during crater formation. [Preview Abstract] |
Wednesday, March 16, 2016 9:24AM - 9:36AM |
K53.00008: Scaling of liquid-drop impact craters in granular media Runchen Zhao, Qianyun Zhang, Hendro Tjugito, Ming Gao, Xiang Cheng Granular impact cratering by liquid drops is a ubiquitous phenomenon, directly relevant to many important natural and industrial processes such as soil erosion, drip irrigation, and dispersion of micro-organisms in soil. Here, by combining the high-speed photography with high precision laser profilometry, we investigate the liquid-drop impact dynamics on granular surfaces and monitor the morphology of resulting craters. Our experiments reveal novel scaling relations between the size of granular impact craters and important control parameters including the impact energy, the size of impinging drops and the degree of liquid saturation in a granular bed. Interestingly, we find that the scaling for liquid-drop impact cratering in dry granular media can be quantitatively described by the Schmidt-Holsapple scaling originally proposed for asteroid impact cratering. On the other hand, the scaling for impact craters in wet granular media can be understood by balancing the inertia of impinging drops and the strength of impacted surface. Our study sheds light on the mechanism governing liquid-drop impacts on dry/wet granular surfaces and reveals a remarkable analogy between familiar phenomena of raining and catastrophic asteroid strikes. [Preview Abstract] |
Wednesday, March 16, 2016 9:36AM - 9:48AM |
K53.00009: Scaling of granular convective velocity and timescale of asteroidal resurfacing Tomoya Yamada, Kousuke Ando, Tomokatsu Morota, Hiroaki Katsuragi Granular convection is one of the well-known phenomena observed in a vertically vibrated granular bed. Recently, the possbile relation between granular convection and asteroidal surface processes has been discussed. The granular convection on the surface of small asteroids might be induced by seismic vibration resulting from meteorite impacts. To quantitatively evaluate the timescale of asteroidal resurfacing by granular convection, the granular convective velocity under various conditions must be revealed. As a first step to approach this problem, we experimentally study the velocity scaling of granular convection using a vertically vibrated glass-beads layer. By systematic experiments, a scaling form of granular convective velocity has been obtained. The obtained scaling form implies that the granular convective velocity can be written by a power-law product of two characteristic velocity components: vibrational and gravitational velocities. In addition, the system size dependence is also scaled. According to the scaling form, the granular convective velocity is almost proportional to gravitatinal acceleration. Using this scaling form, we have estimated the resurfacing timescale on small asteroid surface. [Preview Abstract] |
Wednesday, March 16, 2016 9:48AM - 10:00AM |
K53.00010: The Larger the Viscosity, the Higher the Bounce Menachem Stern, Martin Klein Schaarsberg, Ivo Peters, Kevin Dodge, Wendy Zhang, Heinrich Jaeger A low-viscosity liquid drop can bounce upon impact onto a solid. A high-viscosity drop typically just flattens, i.e., it splats. Surprisingly, our experiments with a droplet made of densely packed glass beads in silicone oil display the opposite behavior: the low-viscosity oil suspension drop splats. The high-viscosity oil suspension bounces. Increasing solvent viscosity {\it increases} the rebound energy. To gain insight into the underlying mechanism, we model the suspension as densely packed elastic spheres experiencing viscous lubrication drag between neighbors. The model reproduces the observed trends. Plots of elastic compression and drag experienced by the particles show that rebounds are made possible by (1) a fraction of the impact energy being stored during initial contact via elastic compression, (2) a rapid broadening of local lubrication drag interactions at the initial impact site into a spatially uniform upward force throughout the drop. Including finite wall drag due to the presence of ambient air into the numerical model diminishes and eventually cuts off the rebound. [Preview Abstract] |
Wednesday, March 16, 2016 10:00AM - 10:12AM |
K53.00011: Percolation velocity dependence on local concentration in bidisperse granular flows Ryan P. Jones, Hongyi Xiao, Zhekai Deng, Paul B. Umbanhowar, Richard M. Lueptow The percolation velocity, $u_{p}$, of granular material in size or density bidisperse mixtures depends on the local concentration, particle size ratio, particle density ratio, and shear rate, $\dot{\gamma}$. Discrete element method computational results were obtained for bounded heap flows with size ratios between 1 and 3 and for density ratios between 1 and 4. The results indicate that small particles percolate downward faster when surrounded by large particles than large particles percolate upward when surrounded by small particles, as was recently observed in shear-box experiments. Likewise, heavy particles percolate downward faster when surrounded by light particles than light particles percolate upward when surrounded by heavy particles. The dependence of $u_{p}/\dot{\gamma}$ on local concentration results in larger percolation flux magnitudes at high concentrations of large (or light) particles compared to high concentrations of small (or heavy) particles, while local volumetric flux is conserved. The dependence of $u_{p}/\dot{\gamma}$ on local concentration can be incorporated into a continuum model, but the impact on global segregation patterns is usually minimal. [Preview Abstract] |
Wednesday, March 16, 2016 10:12AM - 10:24AM |
K53.00012: Impact of Overburden on Segregation in Sheared Granular Flow Alexander M. Fry, Paul B. Umbanhowar, Richard M. Lueptow Dense granular materials tend to segregate into size or density graded regions when subjected to shear. Previous experiments demonstrated that overburden -- normal confining pressure on a granular system -- can slow the rate of size segregation in an annular shear cell. Here, we explore the effects of overburden on sheared granular material through Discrete Element Method (DEM) simulations in a planar shear cell geometry in which shear is applied by a moving bottom wall, while a massive upper wall provides the overburden. Segregation decreases with increasing overburden, but the picture is complicated by concurrent changes in the streamwise velocity profile. To decouple these effects, we also test an idealized system in which a desired streamwise velocity profile -- and therefore shear rate -- is imposed by applying additional horizontal forces to each particle. Based on this approach, we link the effect of overburden on segregation to the grain-scale behavior of the system. Partially funded by Procter \&\ Gamble. [Preview Abstract] |
Wednesday, March 16, 2016 10:24AM - 10:36AM |
K53.00013: Impact of a hydrophobic granular stream in water Brian Utter, Harry Mandeles, Jacob Parkhouse We experimentally investigate the flow of a stream of hydrophobic granular particles impacting a water surface from above. The granular sample is composed of a mixture of hydrophobic and hydrophilic grains and the concentration, stream diameter, and drop height are independently controlled. While granular flows are common in nature and industry, effects of surface chemistry on flow behavior have received relatively little attention. The present experiment complements rheological measurements performed in parallel and aims to elucidate prior experiments on hydrophobic samples in a rotating drum. The present experimental geometry allows us to compare the behavior of granular streams to prior work on impacts of solids and fluid streams. Sequential images of the granular stream in water are taken and analyzed. We present data on the size, length, and shape of the aggregate streams with variations in concentration, entering stream diameter, and drop height. We find that increased hydrophobic grain concentration leads to increased aggregation due to an effectively cohesive interaction mediated by entrained air. At lower concentrations, the stream exhibits a lateral instability. Finally, we will make connections to rheology and rotating drum results. [Preview Abstract] |
Wednesday, March 16, 2016 10:36AM - 10:48AM |
K53.00014: Numerical Simulation and Performance Optimization of a Magnetophoretic Bio-separation chip. Matin Golozar, Jeff Darabi, Majid Molki Separation of micro/nanoparticles is important in biomedicine and biotechnology. This research presents the modeling and optimization of a magnetophoretic bio-separation chip for the isolation of biomaterials, such as circulating tumor cells (CTCs) from the peripheral blood. The chip consists of a continuous flow through microfluidic channels that contains locally engineered magnetic field gradients. The high gradient magnetic field produced by the magnets is spatially non-uniform and gives rise to an attractive force on magnetic particles that move through the flow channel. The computational model takes into account the magnetic and fluidic forces as well as the effect of the volume fraction of particles on the continuous phase. The model is used to investigate the effect of two-way particle-fluid coupling on both the capture efficiency and the flow pattern in the separation chip. The results show that the microfluidic device has the capability of separating CTCs from their native environment. Additionally, a parametric study is performed to investigate the effects of the channel height, substrate thickness, magnetic bead size, bioparticle size, and the number of beads per cell on the cell separation performance. [Preview Abstract] |
Wednesday, March 16, 2016 10:48AM - 11:00AM |
K53.00015: A Statistical investigation of sloshing parameters for multiphase offshore separators Md Mahmud, Rafiqul Khan, Qiang Xu Liquid sloshing in multiphase offshore separators has been the subject of intense investigations for last several decades both by experiments and simulations. Large number scientists have worked to minimize sloshing impacts/intensity and some others have developed new methods to describe the sloshing patterns. In addition, complex mathematical models are developed to characterize sloshing phenomenon. However, a comprehensive statistical study of the input parameters and output results is not yet been studied. In this study, statistical approach will be considered to determine the significant parameters for liquid sloshing. The factor analysis and principal component analysis techniques are considered to identify the significant parameters for liquid sloshing. Numerical experiments are carried out through Computation Fluid Dynamics (CFD) technique using ANSYS Fluent software. The input parameters considered here are liquid depth/tank length ratio, tank acceleration, wave frequencies, amplitudes in various sea state conditions .The measured variables include hydrodynamic force, pressure, moments, turbulent kinetic energy, height of the free surface, vorticity. Mathematical correlations may be developed from the data analysis. [Preview Abstract] |
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