@conference { ISI:000280550300020, title = {Shear induced diffusion in dense granular flows}, booktitle = {IUTAM-ISIMM Symposium on Mathematical Modeling and Physical Instances of Granular Flows}, series = {AIP Conference Proceedings}, volume = {1227}, year = {2010}, note = {IUTAM-ISIMM Symposium on Mathematical Modeling and Physical Instances of Granular Flows, Reggio Calabria, ITALY, SEP 14-18, 2009}, month = {JUN}, pages = {221-229}, publisher = {IUTAM; ISIMM; Italian Inst Higher Math; US Natl Sci Fdn; Reg Council Reggio Calabria; Prov Reggio Calabria; Mediterranean Univ Reggio Calabria}, organization = {IUTAM; ISIMM; Italian Inst Higher Math; US Natl Sci Fdn; Reg Council Reggio Calabria; Prov Reggio Calabria; Mediterranean Univ Reggio Calabria}, address = {2 Huntington Quadrangle, STE 1NO1, Melville, NY 11747-4501 USA}, abstract = {

The dynamics of dense granular flows subjected to gravity induced shear are investigated experimentally using the refractive index matching technique. The system consists of grains flowing inside a bin with a rectangular cross-section and sheared by a rough boundary on one side and smooth boundaries on the remaining sides. The particles flow within a viscous interstitial liquid having the same refractive index as particles and are imaged in the bulk using laser fluorescence. The particle positions are identified very accurately and tracked over long durations to obtain the mean and fluctuating properties. The shear is observed to be non-linear and localized in a region of 3 to 4 particles near the boundary. The boundary imposes a packing order, and the grains are observed to flow in layers, parallel to the shearing boundary, which get progressively more disordered with distance from the walls. We have also carried out soft particle simulations in a equivalent system incorporating the Cundall-Strack contact model between the particles and ignoring the hydrodynamic effects of the interstitial liquid to understand the effect of particle friction coefficient, elasticity, contact model and polydispersity on the mean and fluctuating flow properties. We find the mean velocity and the number density of the particles as a function of flow cross-section and the particle fluctuation properties observed in the experiments and the simulations to in very good agreement after appropriate scaling.

}, keywords = {DEM, Diffusion, granular, index matching, LAMMPS, laser fluorescence}, isbn = {978-0-7354-0772-5}, issn = {0094-243X}, doi = {10.1063/1.3435393}, author = {Orpe, Ashish V. and Rycroft, Chris H. and Kudrolli, Arshad A.}, editor = {Goddard, J. D. and Jenkins, J. T. and Giovine, P.} } @article { ISI:000348532300001, title = {Spontaneous jamming and unjamming in a hopper with multiple exit orifices}, journal = {Physical Review E}, volume = {90}, number = {2}, year = {2014}, month = {AUG}, pages = {020201}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {

We show that the flow of granular material inside a two-dimensional flat bottomed hopper is altered significantly by having more than one exit orifice. For hoppers with small orifice widths, intermittent flow through one orifice enables the resumption of flow through the adjacent jammed orifice, thus displaying a sequence of jamming and unjamming events. Using discrete element simulations, we show that the total amount of granular material (i.e., avalanche size) emanating from all the orifices combined can be enhanced by about an order of magnitude difference by simply adjusting the interorifice distance. The unjamming is driven primarily by fluctuations alone when the interorifice distance is large, but when the orifices are brought close enough, the fluctuations along with the mean flow cause the flow to unjam.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.90.020201}, author = {Kunte, Amit and Doshi, Pankaj and Orpe, Ashish V.} } @article {44231, title = {Spreading dynamics of superposed liquid drops on a spinning disk}, journal = {Physics of Fluids}, volume = {30}, year = {2018}, month = {JAN}, pages = {012110}, type = {Article}, abstract = {

We have experimentally studied simultaneous spreading of superposed drops of two Newtonian liquids on top of a horizontal spinning disk using the flow visualization technique. An inner drop of high surface tension liquid is placed centrally on the disk followed by a drop of outer liquid (lower surface tension) placed exactly above that. The disk is then rotated at a desired speed for a range of volume ratios of two liquids. Such an arrangement of two superposed liquid drops does not affect the spreading behavior of the outer liquid but influences that of the inner liquid significantly. The drop spreads to a larger extent and breaks into more fingers (Nf) as compared to the case where the same liquid is spreading in the absence of outer liquid. The experimentally observed number of fingers is compared with the prediction using available theory for single liquid. It is found that the theory over-predicts the value of Nf for the inner liquid while it is covered by an outer liquid. We provide a theoretical justification for this observation using linear stability analysis. Our analysis demonstrates that for small but finite surface tension ratio of the two liquids, the presence of the outer interface reduces the value of the most unstable wave number which is equivalent to the decrease in the number of fingers observed experimentally. Finally, sustained rotation of the disk leads to the formation of droplets at the tip of the fingers traveling outwards. Published by AIP Publishing.

}, issn = {1070-6631}, doi = {10.1063/1.5002601}, author = {Sahoo, Subhadarshinee and Orpe, Ashish V. and Doshi, Pankaj} } @article {47459, title = {Slip behavior during pressure driven flow of Laponite suspension}, journal = {Physics of Fluids}, volume = {33}, year = {2021}, month = {MAY}, type = {Article}, abstract = {

We investigate pressure driven pipe flow of Laponite suspension, as a model thixotropic fluid. The tendency of the suspension to age is controlled by addition of sodium chloride salt to vary the ionic strength. We use a syringe pump to prescribe the flow and observe that a steady state flow is obtained. Unusually, the steady state pressure drop required to maintain a constant flow rate decreases with an increase in the flow rate, in qualitative contrast to the expectation for Poiseuille flow. We demonstrate that experimental results obtained by varying the flow rate, salt concentration, and flow geometry (pipe diameter and length) can be collapsed onto a single universal curve that can be rationalized by invoking slip of the suspension at the tube walls. The Laponite suspension exhibits plug-like flow, yielding at the tube walls. Our results suggest that the slip length varies linearly with the flow rate and inversely with the tube diameter.

}, doi = {10.1063/5.0051044}, author = {Kamdi, Prophesar M. and Orpe, Ashish V. and Kumaraswamy, Guruswamy} }