@article {42615, title = {Friction of a slider on a granular layer: non-monotonic thickness dependence and effect of boundary conditions}, journal = {Physical Review E}, volume = {73}, year = {2006}, month = {JAN}, pages = {010301}, type = {Article}, abstract = {

We investigate the effective friction encountered by a mass sliding on a granular layer as a function of bed thickness and boundary roughness conditions. The observed friction has minima for a small number of layers before it increases and saturates to a value that depends on the roughness of the sliding surface. We use an index-matched interstitial liquid to probe the internal motion of the grains with fluorescence imaging in a regime where the liquid has no significant effect on the measured friction. The shear profiles obtained as a function of depth show a decrease in slip near the sliding surface as the layer thickness is increased. We propose that the friction depends on the degree of grain confinement relative to the sliding surfaces.

}, doi = {10.1103/PhysRevE.73.010301}, author = {Siavoshi, Saloome and Orpe, Ashish V. and Kudrollim, Arshad} } @article { ISI:000263598900010, title = {Fast decay of the velocity autocorrelation function in dense shear flow of inelastic hard spheres}, journal = {EPL}, volume = {84}, number = {6}, year = {2008}, month = {DEC}, pages = {64003}, publisher = {EDP SCIENCES S A}, type = {Article}, address = {17, AVE DU HOGGAR, PA COURTABOEUF, BP 112, F-91944 LES ULIS CEDEX A, FRANCE}, abstract = {

We find in complementary experiments and event-driven simulations of sheared inelastic hard spheres that the velocity autocorrelation function psi(t) decays much faster than t(-3/2) obtained for a fluid of elastic spheres at equilibrium. Particle displacements are measured in experiments inside a gravity-driven flow sheared by a rough wall. The average packing fraction obtained in the experiments is 0.59, and the packing fraction in the simulations is varied between 0.5 and 0.59. The motion is observed to be diffusive over long times except in experiments where there is layering of particles parallel to boundaries, and diffusion is inhibited between layers. Regardless, a rapid decay of psi(t) is observed, indicating that this is a feature of the sheared dissipative fluid, and is independent of the details of the relative particle arrangements. An important implication of our study is that the non-analytic contribution to the shear stress may not be present in a sheared inelastic fluid, leading to a wider range of applicability of kinetic theory approaches to dense granular matter. Copyright (C) EPLA, 2008

}, issn = {0295-5075}, doi = {10.1209/0295-5075/84/64003}, author = {Orpe, Ashish V. and Kumaran, V. and Reddy, K. Anki and Kudrolli, Arshad} } @article { ISI:000305276600039, title = {Flow-induced channelization in a porous medium}, journal = {EPL}, volume = {98}, number = {5}, year = {2012}, month = {JUN}, pages = {58003}, publisher = {EPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETY}, address = {6 RUE DES FRERES LUMIERE, MULHOUSE, 68200, FRANCE}, abstract = {

Flow through a saturated, granular, porous medium can lead to internal erosion, preferential flow enhancement, and the formation of channels within the bulk of the medium. We examine this phenomenon using a combination of experimental observations, continuum theory and numerical simulations in a minimal setting. Our experiments are carried out by forcing water through a Hele-Shaw cell packed with bidisperse grains. When the local flow-induced stress exceeds a critical threshold, the smaller grains are dislodged and transported. This changes the porosity of the medium, thence, the local hydraulic conductivity, and leads to the development of erosional channels. Erosion is ultimately arrested due to the drop in the mean pressure gradient, while most of the flow occurs through the channels. We describe this using a minimal multiphase description of erosion where the volume fraction of the fluid, mobile, and immobile, grains change in space and time. Numerical solutions of the resulting initial boundary value problem yield results for the dynamics and morphology that are in qualitative agreement with our experiments. In addition to providing a basis for channelization in porous media, our study highlights how heterogeneity in porous media may arise from flow as a function of the erosion threshold. Copyright (C) EPLA, 2012

}, issn = {0295-5075}, doi = {10.1209/0295-5075/98/58003}, author = {Mahadevan, A. and Orpe, Ashish V. and Kudrolli, A. and Mahadevan, L.} } @article { ISI:000346833500005, title = {Flow of granular matter in a silo with multiple exit orifices: jamming to mixing}, journal = {Physical Review E}, volume = {90}, number = {6}, year = {2014}, month = {DEC}, pages = {062206}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {

We investigate the mixing characteristics of dry granular material while draining down a silo with multiple exit orifices. The mixing in the silo, which otherwise consists of noninteracting stagnant and flowing regions, is observed to improve significantly when the flow through specific orifices is stopped intermittently. This momentary stoppage of flow through the orifice is either controlled manually or is chosen by the system itself when the orifice width is small enough to cause spontaneous jamming and unjamming. We observe that the overall mixing behavior shows a systematic dependence on the frequency of closing and opening of specific orifices. In particular, the silo configuration employing random jamming and unjamming of any of the orifices shows early evidence of chaotic mixing. When operated in a multipass mode, the system exhibits a practical and efficient way of mixing particles.

}, issn = {1539-3755}, doi = {10.1103/PhysRevE.90.062206}, author = {Kamath, Sandesh and Kunte, Amit and Doshi, Pankaj and Orpe, Ashish V.} } @article { ISI:000379040200026, title = {Fingering instability of a suspension film spreading on a spinning disk}, journal = {Physics of Fluids}, volume = {28}, number = {6}, year = {2016}, month = {JUN}, pages = {063303}, publisher = {AMER INST PHYSICS}, type = {Article}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {

The spreading of a thin film of suspension on a spinning disk and the accompanying contact line instability is studied through flow visualization experiments. The critical radius for the onset of instability shows an increase with increase in the particle fraction (phi(p)) before decreasing slightly at the highest value of phi(p) studied, while the instability wavelength (lambda) exhibits a non-monotonic dependence. The value of lambda is close to that for a partially wetting liquid at lower phi(p), it decreases with increasing phi(p) to a minimum before increasing again at largest phi(p). The non-monotonic trends observed for lambda are discussed in light of the linear stability analysis of thin film equations derived for suspensions by Cook et al. [{\textquoteright}{\textquoteright}Linear stability of particle-laden thin films,{\textquoteright}{\textquoteright} Eur. Phys. J.: Spec. Top. 166, 77 (2009)] and Balmforth et al. [{\textquoteright}{\textquoteright}Surface tension driven fingering of a viscoplastic film,{\textquoteright}{\textquoteright} J. Non Newtonian Fluid Mech. 142, 143 (2007)]. Published by AIP Publishing.

}, issn = {1070-6631}, doi = {10.1063/1.4953174}, author = {Kulkarni, Mayuresh and Sahoo, Subhadarshinee and Doshi, Pankaj and Orpe, Ashish V.} } @article {46067, title = {Friction-mediated flow and jamming in a two-dimensional silo with two exit orifices}, journal = {Physical Review E}, volume = {100}, year = {2019}, month = {JUL }, pages = {012901}, type = {Article}, abstract = {

We show that the interparticle friction coefficient significantly influences the flow and jamming behavior of granular materials exiting through the orifice of a two-dimensional silo in the presence of another orifice located in its vicinity. The fluctuations emanating from a continuous flow through a larger orifice results in an intermittent flow through the smaller orifice consisting of sequential jamming and flowing events. The mean time duration of jammed and flow events, respectively, increase and decrease monotonically with increasing interparticle friction coefficient. The frequency of unjamming instances (n(u)), however, shows a nonmonotonic behavior comprising an increase followed by a decrease with increasing friction coefficient. The decrease on either side of the maximum, then, represents a system moving progressively towards a permanently jammed or a permanently flowing state. The overall behavior shows a systematic dependence on the interorifice distance, which determines the strength of the fluctuations reaching the smaller orifice leading to unjamming instances. The probability distributions of jamming and flowing times are nearly similar for different combinations of friction coefficients and interorifice distances studied and, respectively, exhibit exponential and power-law tails.

}, issn = {2470-0045}, doi = {10.1103/PhysRevE.100.012901}, author = {Orpe, Ashish V. and Doshi, Pankaj} } @article {49078, title = {Flow and clogging behavior of a mixture of particles in a silo}, journal = {Physics of Fluids }, volume = {36}, year = {2024}, month = {MAY}, type = {Article}, abstract = {

We investigated the clogging behavior observed during the flow of aspherical particles from a silo in the presence of spherical particles of different sizes and proportions using flow visualization experiments and discrete element method simulations. The size of the avalanche, essentially the tendency of clogging, exhibits non-monotonic dependence on the spherical particle volume fraction. For small enough content of spherical particles, the clogging tendency intensifies, whereas it reduces rapidly for high enough spherical particle fractions, with a minimum in between. The non-monotonic behavior is observed to persist over for different spherical particle sizes. The overall behavior is shown to arise due to competing effects between the localized total particle fraction influencing avalanche strength and mean size of the particles exiting the silo, influencing the probability of arch formation.

}, issn = {1070-6631}, doi = {10.1063/5.0205141}, author = {Bhure, Sukhada C. and Doshi, Pankaj and Orpe, Ashish V.} }