Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session M24: Granular Flows: General 
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Room: 2003 
Tuesday, November 25, 2014 8:00AM  8:13AM 
M24.00001: Imaging Forces in a ThreeDimensional Granular Material Jonathan Bares, Joshua Dijksman, Nicolas Brodu, Robert Behringer We experimentally study the quasistatic deformation of a threedimensional sphere packings subjected to macroscopic deformation. We perform these experiments on slightly polydisperse and nearly frictionless soft hydrogel spheres in a modified triaxial shear apparatus. We resolve the microscopic force and displacement network in a this three dimensional packing through imaging the entire packing at different loading steps. By resolving particle deformations via custom written image analysis software, we extract all particle contacts and contact forces with a very good accuracy. In addition, we measure boundary stresses during compression and shear. We address the nonlinear force response of a disordered packing under compression and shear, force network dynamics and explore the plastic rearrangements inside cyclically sheared and compressed packings. [Preview Abstract] 
Tuesday, November 25, 2014 8:13AM  8:26AM 
M24.00002: Threedimensional particle tracking velocimetry applied to granular flows down rotating chutes Herman Clercx, Sushil Shirsath, Johan Padding, Hans Kuipers We report on the crossvalidation of 3D particle tracking velocimetry (3DPTV) with other measurement techniques, such as particle image velocimetry (PIV), electronic ultrasonic sensor measurements for bed height and the discrete element model (DEM), for gaining more insight into the behavior of granular flows down inclined rotating chutes. In particular we aim at gaining access to Lagrangian displacement data of surface particles in granular flows and to obtain independent measurements of both the surface velocity and the bed height in the chute. The 3DPTV method is based on imaging and tracking colored tracer particles that are introduced in the granular material, which are viewed from three directions. The three cameras collect consecutive frames a known $\Delta $t apart and the PTV algorithm for locating and tracking particles is used to determine particle trajectories and velocities. The PTV and PIV results are in good mutual agreement with regard to the streamwise and spanwise surface velocity. The particle bed height obtained from 3DPTV was compared with data from an ultrasonic bedheight sensor and it is found to be in good mutual agreement, as was the case for the comparison between the experimental findings from 3DPTV and simulations by DEM. [Preview Abstract] 
Tuesday, November 25, 2014 8:26AM  8:39AM 
M24.00003: Electrical charging in shaken granular media Freja Nordsiek, Daniel Lathrop Results are presented on the electrical charging of granular media shaken between two conducting plates. Voltage measurements were taken between the plates for both monodisperse and bidisperse sets of particles of different materials with diameters in the 100 micron to 1 mm range. Particle charging was observed through capacitive coupling with the plates and electrical discharges. The following results were observed: 1) a monotonic increase in charging with shaking strength, 2) a threshold in the number of particles of filling the cell with about one layer of particles to see charging, 3) material and diameter differences causing an order of magnitude spread in measured signal, and 4) long time scale transients. The influence of collective effects and the potential relevance to natural charging phenomena seen in sand storms, volcanic ash clouds, thunderstorms, and thundersnow are discussed. [Preview Abstract] 
Tuesday, November 25, 2014 8:39AM  8:52AM 
M24.00004: Statistics from granular stickslip experiments Aghil Abed Zadeh, Jonathan Bares, Robert P. Behringer We carry out experiments to characterize stickslip 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 as well as the slider's acceleration by a force sensor attached to the spring and accelerometers on the slider. The distributions of energy release and time duration of avalanches during slip obey power laws. We apply a novel event recognition approach using wavelets to extract the avalanche properties. We compare statistics from the wavelet approach with those obtained by typical methods, to show how noise can change the distribution of events. We analyze the power spectrum of various quantities to understand the effect of the loading speed and of the spring stiffness on the statistical behavior of the system. Finally, from a more local point of view and by using a high speed camera and the photoelastic properties of our particles, we characterize the internal granular structure during avalanches. [Preview Abstract] 
Tuesday, November 25, 2014 8:52AM  9:05AM 
M24.00005: Preventing shear thickening in granular suspensions by enhancing hydrodynamic interactions Qin Xu, Sayantan Majumdar, Heinrich Jaeger As a critical volume fraction is approached, granular suspensions can increase their viscosity dramatically under rapid shear; i.e., they exhibit Discontinuous Shear Thickening (DST). Previous works show that this phenomenon is related to frictional particle interactions and the formation of force chains that span the system, similar to dry granular materials. However, frictional contacts can be possibly reduced by lubrication. We experimentally studied the flow dynamics of dense granular suspensions in highly viscous liquids. By combining rheological measurements and fast imaging techniques, we characterized the flow curves for different liquid viscosities $\eta_0$. We found that shear thickening becomes weaker with $\eta_0$ and eventually disappears for highly viscous solvent. In this regime, the suspensions show a Newtonianlike behavior with constant viscosity under shear. The crossover from granular to Newtonian regimes reflects the competition between friction and hydrodynamics. [Preview Abstract] 
(Author Not Attending)

M24.00006: NonNewtonian stress tensor and thermal conductivity tensor in granular plane shear flow Meheboob Alam, Saikat Saha The nonNewtonian stress tensor and the heat flux in the plane shear flow of smooth inelastic disks are analysed from the Gradlevel moment equations using the anisotropic Gaussian as a reference. Closedform expressions for shear viscosity, pressure, first normal stress difference (${\mathcal N}_1$) and the dissipation rate are given as functions of (i) the density or the area fraction ($\nu$), (ii) the restitution coefficient ($e$), (iii) the dimensionless shear rate ($R$), (iv) the temperature anisotropy [$\eta$, the difference between the principal eigenvalues of the second moment tensor] and (v) the angle ($\phi$) between the principal directions of the shear tensor and the second moment tensor. Particle simulation data for a sheared harddisk system is compared with theoretical results, with good agreement for $p$, $\mu$ and ${\mathcal N}_1$ over a large range of density. In contrast, the predictions from a NavierStokes order constitutive model are found to deviate significantly from both the simulation and the moment theory even at moderate values of $e$. We show that the gradient of the deviatoric part of the kinetic stress drives a heat current and the thermal conductivity is characterized by an anisotropic 2nd rank tensor for which explicit expressions are derived. [Preview Abstract] 

M24.00007: ABSTRACT WITHDRAWN 
Tuesday, November 25, 2014 9:31AM  9:44AM 
M24.00008: Predictive simulation of granular flows applied to compressible multiphase flow modeling Ryan J. Goetsch, Jonathan D. Regele Multiphase flows have been an active area of research for decades due to their complex nature and occurrence in many engineering applications. However, little information exists about the dense compressible flow regime. Recent experimental work [Wagner {\it et al.}, Exp. Fluids {\bf 52}, 1507 (2012)] using a multiphase shock tube has studied gassolid flows with high solid volume fractions ($\alpha=0.2$) by measuring shock waveparticle cloud interactions. It is still unclear what occurs at the particle scale inside and behind the particle cloud during this interaction. The objective of this work is to perform direct numerical simulations to understand this phenomena. With this goal in mind, a discrete element method (DEM) solver was developed to predict the properties of a particle cloud formed by gravity driven granular flow through a slit opening. For validation purposes, the results are compared with experimental channel flow data. It is found that the mean velocity profile and mass flow rates correlate well with the experiment, however the fluctuation velocities are significantly underpredicted for both smooth and rough wall cases. [Preview Abstract] 
Tuesday, November 25, 2014 9:44AM  9:57AM 
M24.00009: Anomalous effects in granular Poiseuille flow: temperature bimodality and Knudsen minima Deepthi Shivanna, Meheboob Alam Two wellknown rarefaction effects, the {\it Knudsen minima} and the {\it bimodality} of the temperature profile, are investigated in the granular analog of the Poiseuille flow via eventdriven simulations of smooth inelastic harddisks under gravity. The appearance of the bimodalshape of the granular temperature is found to depend crucially on wall conditions: the bimodality is most prominent for the intermediate case between the specular and the bounceback wallparticle collisions. The dependences of the height of the temperature maxima and its location (from the center of the channel) on the restitution coefficient are in variance with the related kinetic theory predictions (Tij \& Santos, J.~Stat.~Phys.~2004). For the Poiseuille flow of a rarefied gas, it is known that the mass flow rate decreases with increasing Knudsen number ($Kn$), reaches a minimum at $Kn\sim O(1)$ and increases again with further increase in $Kn$ this is dubbed {\it Knusden minima}. In a granular Poiseuille flow we show that this Knudsen minima is absent. The origin of these anomalous behaviour is shown to be tied to dissipationinduced particleclustering in the channel. [Preview Abstract] 
Tuesday, November 25, 2014 9:57AM  10:10AM 
M24.00010: The Effect of Particle Size on the Erosion of Lunar Regolith from a Spacecraft Landing Kyle Berger, Brendan Brown, Philip Metzger, Christine Hrenya The ejection of regolith from a spacecraft landing on an extraterrestrial body (Moon, Mars, etc.) can be extremely hazardous to anything near or possibly even far from the landing point. Models currently being used to describe this phenomenon use single particle trajectories and thus ignore the effects of interparticle collisions. We seek to improve those models by incorporating the effects of collisions. We model the system using the discrete element method (DEM), which models the particles individually using Newton's laws and thus explicitly includes interparticle collisions. The current study focuses on the effect of particle size, both in monodisperse systems, as well as polydisperse systems using binary and continuous particle size distributions (PSDs). While collisions above the surface are rare in the monodisperse case (about 0.0001{\%} of eroded particles), they are relatively frequent in the binary case, particularly between unlike particle species (about 15{\%} of eroded large particles). It is expected that as the size disparity becomes larger, which is the case for lunar regolith as it spans at least three orders of magnitude in size, this effect becomes enhanced. Differences in particle size can result in differences in velocity, leading to interesting phenomena. [Preview Abstract] 
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