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 G30: Granular Flows: General |
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Chair: Marie-Julie Dalbe, Massachusetts Institute of Technology Room: F151 |
Monday, November 21, 2016 8:00AM - 8:13AM |
G30.00001: Deformation of a 3D granular media caused by fluid invasion Marie-Julie Dalbe, Ruben Juanes Multiphase flow in porous media plays a fundamental role in many natural and engineered subsurface processes. The interplay between fluid flow, medium deformation and fracture is essential in geoscience problems as disparate as fracking for unconventional hydrocarbon production, conduit formation and methane venting from lake and ocean sediments, and desiccation cracks in soil. Several experimental and computational studies have shown that the competition between capillary and friction forces can lead to different regimes of deformation, from frictional fingering to hydro-capillary fracturing (Sandnes et al., Nat. Comm. 2011, Holtzman et al., PRL 2012). Most of these investigations have focused, however, on 2D or quasi-2D systems. Here, we develop an experimental set-up that allows us to observe two-phase flow in a fully 3D granular bed and measure the fluid pressure while controlling the level of confining stress. We use an index matching technique to directly visualize the injection of a liquid in a granular media saturated with another, immiscible liquid. We extract the deformation the whole granular bulk as well as at the particle level. Our results show the existence of different regimes of invasion patterns depending on key dimensionless groups that control the system. [Preview Abstract] |
Monday, November 21, 2016 8:13AM - 8:26AM |
G30.00002: Electrification and Charge Distribution in Vertically Shaken Granular Media. Ruben Rojas, Freja Nordsiek, Daniel Lathrop Granular charging of particle laden flows at large scales is a widespread phenomenon and has long been observed in nature: Volcanic ash clouds, desert sandstorms, dust devils, thunderstorms and snowstorms all undergo electrification at large scale. As a first approach to understand this phenomenon, we confined granular particles to a vertically oscillating cylindrical chamber with top and bottom conducting plates. Long term voltage transients between the plates and a high dependence on the total particle surface area suggested the preponderance of collective effects in the electrification processes. In order to further explore this hypothesis, we reduced the electrode area for the measurement with two 2-cm circular flat probes on the top plate. With this setup we detected differences in the charge distribution among the particles due to a more localized measurement of the voltage. [Preview Abstract] |
Monday, November 21, 2016 8:26AM - 8:39AM |
G30.00003: Avalanches and local force evolution in a granular stick-slip experiment Aghil Abed Zadeh, Jonathan Bares, Robert Behringer We perform a stick-slip experiment to characterize avalanches for granular materials. In our experiment, a constant speed stage pulls a slider which rests on a vertical bed of circular photoelastic particles in a 2D system. The stage is connected to the slider by a spring. We measure the force on the spring by a force sensor attached to the spring. We study the PDF of energy release and slip size, avalanche shape in time, and other seismicity laws during slip avalanches. We analyze the power spectrum of the force signal and probability distributions to understand the effect of the loading speed and of the spring stiffness on the statistical behavior of the system. From a more local point of view and by using a high speed camera and the photoelastic properties of our particles, we characterize the local stress change and flow of particles during avalanches. By image processing we detect the avalanches, as connected components in space and time, and the energy dissipation inside the granular medium and their PDFs. The PDFs of avalanches obey power laws both at global and local scales, but with different exponents. We try to understand the distribution and correlation of local avalanches in space and the way they coarse grain to the global avalanches. [Preview Abstract] |
Monday, November 21, 2016 8:39AM - 8:52AM |
G30.00004: Vibrational Collapse of Hexapod Packings Yuchen Zhao, Jingqiu Ding, Jonathan Bar\'{e}s, karola Dierichs, Robert Behringer Columns made of convex noncohesive grains like sand collapse after being released from a confining container. However, structures built from concave grains can be stable without external support. Previous research show that the stability of the columns depends on column diameter and height, by observing column stability after carefully lifting their confinement tubes. Thinner and taller columns collapse with higher probability. While the column stability weakly depends on packing density, it strongly depends on inter-particle friction. Experiments that cause the column to collapse also reveal similar trends, as more effort (such as heavier loading or shearing) is required to destabilize columns that are intrinsically more stable. In the current experiments, we invesitage the effect of vibration on destructing a column. Short columns collapse following the relaxation dynamics of disorder systems, which coincides with similar experiments on staple packings. However, tall columns collapse faster at the beginning, in addition to the relaxation process coming after. Using high-speed imaging, we analyze column collapse data from different column geometries. Ongoing work is focusing on characterizing the stability of hexapod packings to vibration. [Preview Abstract] |
Monday, November 21, 2016 8:52AM - 9:05AM |
G30.00005: Dynamic intermittency in discrete erodible-bed avalanches Matthew Arran, Nathalie Vriend The coexistence of fluid-like and solid-like behaviour in granular matter allows avalanches of grains to flow on the surface of a static but erodible bed. For sufficiently slow inflow, these avalanches are discrete, with previous experimentalists reporting that avalanche fronts pass a given point quasi-periodically. We report instead observations of dynamic intermittency between two regimes, one in which avalanches occur quasi-periodically and another in which the intervals between them are irregular. Finding the first regime consistent with existing models, we introduce a model for the second regime within the framework of Self-Organised Criticality, and describe the transition between the regimes with reference to the state of the erodible bed. [Preview Abstract] |
Monday, November 21, 2016 9:05AM - 9:18AM |
G30.00006: Plowing of granular surface by a vertical blade Vachitar Singh Judge, Emilie Dressaire, Alban Sauret The interaction of a blade with a layer of fluid is an important industrial problem involved in coating of substrates, removing of snow, plowing the fields for agriculture.~Most experimental and theoretical work has focused on the drag and lift forces on plowing blade as it is dragged on a granular surface or studying the flow of the fluid while plowing. However the study of~deformation of a granular surface by a vertical plow blade~has received less attention, despite significant practical and fundamental implications. In this study, we investigate experimentally the behavior of a granular substrate as a vertical plow blade of finite width is translated at constant speed. The vertical blade~directs the granular material outward and sand piles form on either sides.~We characterize the dynamics of plowing by measuring and rationalizing the influence of the width of the vertical plow blade, the height of the plow blade, and the depth granular substrate. [Preview Abstract] |
Monday, November 21, 2016 9:18AM - 9:31AM |
G30.00007: Characteristic correlation study of UV disinfection performance for ballast water treatment Te Ba, Hongying Li, Hafiiz Osman, Chang-Wei Kang Characteristic correlation between ultraviolet disinfection performance and operating parameters, including ultraviolet transmittance (UVT), lamp power and water flow rate, was studied by numerical and experimental methods. A three-stage model was developed to simulate the fluid flow, UV radiation and the trajectories of microorganisms. Navier-Stokes equation with k-epsilon turbulence was solved to model the fluid flow, while discrete ordinates (DO) radiation model and discrete phase model (DPM) were used to introduce UV radiation and microorganisms trajectories into the model, respectively. The UV dose statistical distribution for the microorganisms was found to move to higher value with the increase of UVT and lamp power, but moves to lower value when the water flow rate increases. Further investigation shows that the fluence rate increases exponentially with UVT but linearly with the lamp power. The average and minimum resident time decreases linearly with the water flow rate while the maximum resident time decrease rapidly in a certain range. The current study can be used as a digital design and performance evaluation tool of the UV reactor for ballast water treatment. [Preview Abstract] |
Monday, November 21, 2016 9:31AM - 9:44AM |
G30.00008: An Experiment Study about Forces and Shapes of Liquid bridges for Micron-particles. Huang Zhang, Shuiqing Li Wet micro-particles are often encountered in the electrostatic precipitator and fiber filtration system. The liquid bridges formed between wet granules are leading to change the flow or packing behavior of micro-particles. Firstly, the magnitude of liquid bridge force between a micron-particle and a plate is measured by atomic force microscope (AFM). The AFM tip is adopted as the sphere tip instead of the sharp one. As the humidity increases, the shape of liquid bridge between this particle and the plate is observed by confocal laser scanning microscopy (CLSM). Secondly, a suspension containing micro-particles are painting on a plate to form particles layers. As humidity increases, AFM is used to measure the forces between the sphere tip and the micro-particles in the layers. At the same time, the shape of liquid bridges is observed to see whether the bridges are formed as pendular, funicular and capillary ones by CLSM. Finally, it is found out that liquid bridges are hardly existed below a critical humidity, and the force between particles also grows slowly. Beyond this critical humidity, a sudden increase of the liquid bridge force is exhibited. Liquid forces are also compared between different shapes of liquid bridges. [Preview Abstract] |
Monday, November 21, 2016 9:44AM - 9:57AM |
G30.00009: Effects of hydrodynamic interaction on random adhesive loose packings of micron-sized particles Wenwei Liu, Ran Tao, Sheng Chen, Huang Zhang, Shuiqing Li Random loose packings of uniform spherical micron-sized particles under a uniform flow field are investigated via an adhesive discrete-element method with the two-way coupling of both the particles and the fluid. Characterized by a dimensionless adhesion parameter $Ad$, the packing fraction follows the similar law to that without fluid, but results in larger values due to the hydrodynamic compression. The total pressure drop through the packed bed increases with the packing fraction and agrees well with the theoretical predictions of Ergun function. The effects of different parameters, such as flow velocity, particle size and surface energy, on packing fraction and pressure drop take place through different ways, which can be associated with the local mechanical equilibrium in the presence of fluid. [Preview Abstract] |
Monday, November 21, 2016 9:57AM - 10:10AM |
G30.00010: Phase Transitions and Metastability in Self-Propelled Particle systems. Ajinkya Kulkarni, Sumesh Thampi, Mahesh Panchagnula Ordered motion of self-propelling micro-organisms produce interesting patterns. The objective of this study is to investigate the nature of the transition from disorganized thermal-like motion to organized vortical motion, and the resulting metastability in systems of self-propelled particles. A modified version of the Standard Vicsek Model has been used, where the particles are modeled as soft disks with finite mass, confined in a circular domain. We observe multiple phases as the local co-ordination coefficient is varied. We analyze the nature of transitions by calculating Binder Cumulants of the order parameters. An occurrence of metastability is investigated in the hysteretic region. The switching between the steady states of the system in the hysteretic region has been triggered via artificial nucleation of randomly picked particles spanning the entire domain. In addition, the effect of domain size on the nature of the phase transitions has been studied. Finally the motivation for these phase transitions has been explained via thrust generation ability and the geometry of the confinement. [Preview Abstract] |
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