Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session G11: Granular Flows II |
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Chair: Wendy Zhang, University of Chicago Room: 314 |
Monday, November 21, 2011 8:00AM - 8:13AM |
G11.00001: Still waters: deadzone formation in granular jet impact Jake Ellowitz, Herve Turlier, Nicholas Guttenberg, Wendy W. Zhang, Sidney R. Nagel When a densely packed jet of non-cohesive grains collides with a target, a deadzone of stagnant particles forms within the jet. Analogous deadzones form when a droplet of dense suspension hits a substrate, a process important in coating and inkjet printing. In a different context, the formation of planets depends on successive collisions and aggregation of centimeter sized dust particles. The growth process is only possible if a deadzone is deposited onto the larger particle. Using experiments, discrete particle simulations and continuum modeling, we elucidate factors leading to deadzone formation in the collisions in noncohesive dense granular jet impact. We find that a frictional fluid model quantitatively reproduces the structure and stresses observed in both experiment and simulation. A deadzone does not form when the target is frictionless. In contrast, when the target shape is changed from a flat circular disk to a cone, the size of the deadzone decreases continuously with the cone angle. [Preview Abstract] |
Monday, November 21, 2011 8:13AM - 8:26AM |
G11.00002: Granular Response to an Impact Lou Kondic, Robert Behringer, Wolfgang Losert, Corey O'Hern In this computational study we discuss response of a granular system to an impact of a large intruder. We find that interaction between the granular particles strongly influences the intruder's dynamics, with particularly strong role played by friction. We will also discuss the dynamics of granular particles to an impact and correlate affine and non-affine components of particles' motion to the dynamics of intruder itself. [Preview Abstract] |
Monday, November 21, 2011 8:26AM - 8:39AM |
G11.00003: Impact Dynamics in a 3D Granular Bed Kerstin Nordstrom, Matt Harrington, Wolfgang Losert Granular impacts have been studied for many years in the scientific community. Force laws have been characterized for different systems including universal scaling relations by Katsuragi and Durian. Despite this, little is known regarding the microscopic origin of these observations. In this work, we study the impact of a projectile onto a bed of 3 mm grains immersed in an index-matched fluid. Using a laser sheet scanning technique, a high speed camera, and particle tracking, we can measure the trajectory of each grain throughout an impact event. We have characterized the nonaffine motion within the system as a function of projectile shape and initial sample preparation. Our preliminary results show significant nonaffine motion near the impactor. These results are compared and contrasted with recent experiments and simulations involving 2D systems. [Preview Abstract] |
Monday, November 21, 2011 8:39AM - 8:52AM |
G11.00004: ABSTRACT WITHDRAWN |
Monday, November 21, 2011 8:52AM - 9:05AM |
G11.00005: Study of 2D Granular Impact Dynamics with Photoelasic Particles Abe Clark, R.P. Behringer, Lou Kondic What is the response of a granular material to a high speed impact from a foreign object? Our experiments consist of a large 2D granular system which is subjected to impact by an intruder from above. Using photoelastic discs and a high-speed camera (up to 775,000 fps), we are able to observe the dynamics in this process in a way which has not been done previously. We compare results to previous work on this subject, which primarily consists of macroscopic frictional models. We observe phenomena which are not captured by averaged friction models, such as large fluctuations in the acceleration of the intruder as it moves through the granular material. The high frame rates also allow us to observe rich photoelastic behavior, including propagation of acoustic waves. The photoelastic response beneath the intruder and the measured acceleration are well correlated, suggesting that a grain-scale, stick-slip description is necessary to account for the dissipation of the intruder's kinetic energy, and that much of the energy might be carried away by compressional waves. [Preview Abstract] |
Monday, November 21, 2011 9:05AM - 9:18AM |
G11.00006: Dynamics in cohesive granular flow Jennifer Rieser, Wenbin Li, Ju Li, Jerry Gollub, Douglas Durian Inter-particle interactions often have a dramatic effect on granular flow dynamics. Here, we explore the flow resulting from an applied compressive stress on a granular pillar composed of a single layer of particles. Grain-grain attractions within the pillar are governed by tunable capillary forces induced by an interstitial fluid. Both the applied stress and the grain positions are monitored as a function of time. We determine the probability distributions of particle translational and angular velocities, local packing fraction, and the number of nearest neighbors as a function of time. In addition, instantaneous velocities are used to characterize larger scale spatial structures that emerge in the flow from the collective motion of particles. We see a striking dependence on initial conditions, for instance in the development and in the behavior of slip planes, both of which are found to be qualitatively similar to molecular dynamics simulations. [Preview Abstract] |
Monday, November 21, 2011 9:18AM - 9:31AM |
G11.00007: Blowing in the wind: the dynamics of small laboratory-scale dunes Yang Zhang, Willem van de Water Barchan dunes can be found in the desert under steady wind conditions where they translate unaltered in the direction of the wind. These remarkable natural patterns are the result of the interaction between sand and wind where the wind deposits the sand in heaps, which, in turn, change the properties of the turbulent wind. The length scales of these dunes, set by saltation of the grains, can be reduced dramatically by oscillating gravity. This makes laboratory experiments possible. We study the fate of tiny dunes sitting on an oscillating table in the turbulent boundary layer of a wind tunnel. Growth or death of these dunes depends on the influx of sand. Paradoxically, more influx can lead to more erosion. We explain this through a continuum model, and link its unknowns to detailed measurements of grain dynamics. [Preview Abstract] |
Monday, November 21, 2011 9:31AM - 9:44AM |
G11.00008: Avalanche dynamics of dry or fully immersed granular mass and temporal evolution of failure structure Yung-Ta Huang, Fuling Yang This work examines the avalanche process of dry and fully immersed granular mass abruptly released down a laboratory flume (of width 15 cm) of smooth bed at fixed inclination experimentally. The granular mass is composed of identical glass spheres (of diameter 1.6 cm) and Newtonian fluids (water or 200 cP glycerol). High-speed imaging technique was applied to capture individual sphere motion from the flume lateral side. The obtained sphere collective motion show distinctive patters in relation with the failure plane which developed during an avalanche. We also estimate instantaneous bulk velocity distribution by area-averaging of individual sphere velocities. It is observed that the interstitial liquid can enhance bulk basal slip due to lubricating effect. The liquid viscosity also gives rise to a unifying effect on bulk dynamics: sharp interface between moving and stationary spheres can be detected in dry mass but not for the liquid-immersed mass. Lastly, we apply the Coulomb failure criterion developed in soil mechanics for homogeneous infinite static mass to predict the failure plane in current finite mass in unsteady motion. It is found that as long as the basal slip is taken into account, the failure plane can be successfully captured in the dry and the water-immersed avalanches. [Preview Abstract] |
Monday, November 21, 2011 9:44AM - 9:57AM |
G11.00009: ABSTRACT WITHDRAWN |
Monday, November 21, 2011 9:57AM - 10:10AM |
G11.00010: Characterizing titanium powder: morphology, flow and segregation Nicholas A. Pohlman, John A. Roberts, Matthew Gonser Powder metallurgy manufacturing with titanium could achieve near-net shape for parts with high strength-to-weight ratio. However, pure titanium (Ti) powders have large aspect ratios that prevent smooth flow. Features of Ti powder were examined experimentally to understand its limited flowability. The surface morphology was measured using a SEM for both raw powder as well as those made ``uniform'' via milling. The poly-disperse mixture had particle sizes between 45--700~$\mu$m, of which a significant concentration were $<45\mu$m, which results in a very steep and unsteady angle of repose when the powder was placed in a rotating tumbler. The flat surface and steady flow typical of macroscopic particles is not present, but instead has slumping motion as material piles up and collapses intermittently. Spectral analysis indicates that increasing Froude number causes the slumping behavior to move to higher frequencies, but spread over a larger range. Size segregation causes porous streaks to form at the periphery of the tumbler where the angular separation of the streaks decreases with increasing Froude number. The overall conclusion is that more narrow ranges of particle size are necessary to yield usable titanium in powder metallurgy manufacturing. [Preview Abstract] |
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