01362nas a2200157 4500008004100000245011500041210006900156260000800225300001100233490000700244520076300251100002201014700002101036700002201057856012501079 2006 eng d00aFriction of a slider on a granular layer: non-monotonic thickness dependence and effect of boundary conditions0 aFriction of a slider on a granular layer nonmonotonic thickness  cJAN a0103010 v733 a

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.

1 aSiavoshi, Saloome1 aOrpe, Ashish, V.1 aKudrollim, Arshad uhttps://library.ncl.res.in/content/friction-slider-granular-layer-non-monotonic-thickness-dependence-and-effect-boundary01596nas a2200157 4500008004100000245006200041210006200103260000800165300002300173490000700196520109300203100001301296700002101309700002101330856008701351 2007 eng d00aLubrication effects on the flow of wet granular materials0 aLubrication effects on the flow of wet granular materials cAPR aArticle No. 0313020 v763 a

We investigate the dynamics of a partially saturated grain-liquid mixture with a rotating drum apparatus. The drum is partially filled with the mixture and then rotated about its horizontal axis. We focus on the continuous avalanching regime and measure the impact of the volume fraction and viscosity of the liquid on the dynamic surface angle. The inclination angle of the surface is observed to increase sharply to a peak and then decrease as a function of liquid volume fraction. The height of the peak is observed to increase with rotation rate. For higher liquid volume fractions, the inclination angle of the surface can decrease with viscosity before increasing. The viscosity where the minimum occurs decreases with the rotation rate of the drum. Limited measurements of the flow depth were made, and these were observed to show only fractional changes with volume fraction and rotation speeds. We show that the qualitative features of our observations can be understood by analyzing the effect of lubrication forces on the time scale over which particles come in contact.

1 aXu, Qing1 aOrpe, Ashish, V.1 aKudrolli, Arshad uhttps://library.ncl.res.in/content/lubrication-effects-flow-wet-granular-materials03073nas a2200145 4500008004100000245003900041210003900080260000800119300000900127490000800136520266700144100002102811700002402832856007102856 2007 eng d00aRheology of surface granular flows0 aRheology of surface granular flows cJAN a1-320 v5713 a

Surface granular flow, comprising granular material flowing on the surface of a heap of the same material, occurs in several industrial and natural systems. The rheology of such a flow was investigated by means of measurements of velocity and number-density profiles in a quasi-two-dimensional rotating cylinder, half-filled with a model granular material – monosize spherical stainless-steel particles. The measurements were made at the centre of the cylinder, where the flow is fully developed, using streakline photography and image analysis. The stress profile was computed from the number-density profile using a force balance which takes into account wall friction. Mean-velocity and root-mean-square (r.m.s.)-velocity profiles are reported for different particle sizes and cylinder rotation speeds. The profiles for the mean velocity superimpose when distance is scaled by the particle diameter d and velocity by a characteristic shear rate and the particle diameter, where βm is the maximum dynamic angle of repose and βs is the static angle of repose. The maximum dynamic angle of repose is found to vary with the local flow rate. The scaling is also found to work for the r.m.s. velocity profiles. The mean velocity is found to decay exponentially with depth in the bed, with decay length λ = 1.1d. The r.m.s. velocity shows similar behaviour but with λ = 1.7d. The r.m.s. velocity profile shows two regimes: near the free surface the r.m.s. velocity is nearly constant and below a transition point it decays linearly with depth. The shear rate, obtained by numerical differentiation of the velocity profile, is not constant anywhere in the layer and has a maximum which occurs at the same depth as the transition in the r.m.s. velocity profile. Above the transition point the velocity distributions are Gaussian and below the transition point the velocity distributions gradually approach a Poisson distribution. The shear stress increases roughly linearly with depth. The variation in the apparent viscosity η with r.m.s. velocity u shows a relatively sharp transition at the shear-rate maximum, and in the region below this point the apparent viscosity η ∼ u−1.5. The measurements indicate that the flow comprises two layers: an upper low-viscosity layer with a nearly constant r.m.s. velocity and a lower layer of increasing viscosity with a decreasing r.m.s. velocity. The thickness of the upper layer depends on the local flow rate and is independent of particle diameter while the reverse is found to hold for the lower-layer thickness. The experimental data is compared with the predictions of three models for granular flow.

1 aOrpe, Ashish, V.1 aKhakhar, Devang, V. uhttps://library.ncl.res.in/content/rheology-surface-granular-flows01327nas a2200145 4500008004100000245008100041210006900122260000800191300001100199490000700210520081400217100002101031700002101052856010801073 2007 eng d00aVelocity correlations in dense granular flows observed with internal imaging0 aVelocity correlations in dense granular flows observed with inte cJUN a2380010 v983 a

We show that the velocity correlations in uniform dense granular flows inside a silo are similar to the hydrodynamic response of an elastic hard-sphere liquid. The measurements are made using a fluorescent refractive-index-matched interstitial fluid in a regime where the flow is dominated by grains in enduring contact and fluctuations scale with the distance traveled, independent of flow rate. The velocity autocorrelation function of the grains in the bulk shows a negative correlation at short time and slow oscillatory decay to zero similar to simple liquids. Weak spatial velocity correlations are observed over several grain diameters. The mean square displacements show an inflection point indicative of caging dynamics. The observed correlations are qualitatively different at the boundaries.

1 aOrpe, Ashish, V.1 aKudrolli, Arshad uhttps://library.ncl.res.in/content/velocity-correlations-dense-granular-flows-observed-internal-imaging01930nas a2200181 4500008004100000245005900041210005900100260000800159300001000167490000800177520136900185100002901554700002101583700001701604700002101621700002001642856008601662 2008 eng d00aErosion of a granular bed driven by laminar fluid flow0 aErosion of a granular bed driven by laminar fluid flow cJUN a47-580 v6053 a

Motivated by examples of erosive incision of channels in sand, we investigate the motion of individual grains in a granular bed driven by a laminar fluid to give us new insights into the relationship between hydrodynamic stress and surface granular flow. A closed cell of rectangular cross-section is partially filled with glass beads and a constant fluid flux Q flows through the cell. The refractive indices of the fluid and the glass beads are matched and the cell is illuminated with a laser sheet, allowing us to image individual beads. The bed erodes to a rest height hr which depends on Q. The Shields threshold criterion assumes that the non-dimensional ratio θ of the viscous stress on the bed to the hydrostatic pressure difference across a grain is sufficient to predict the granular flux. Furthermore, the Shields criterion states that the granular flux is non-zero only for θ > θc. We find that the Shields criterion describes the observed relationship hr ∝ Q1/2 when the bed height is offset by approximately half a grain diameter. Introducing this offset in the estimation of θ yields a collapse of the measured Einstein number q* to a power-law function of θ − θc with exponent 1.75 ± 0.25. The dynamics of the bed height relaxation are described well by the power-law relationship between the granular flux and the bed stress.

1 aE., Lobkovsky, Alexander1 aOrpe, Ashish, V.1 aMolloy, Ryan1 aKudrolli, Arshad1 aRothman, D., H. uhttps://library.ncl.res.in/content/erosion-granular-bed-driven-laminar-fluid-flow01862nas a2200181 4500008004100000022001400041245010200055210006900157260010300226300001000329490000700339520113400346100002101480700001601501700001601517700002101533856012601554 2008 eng d a0295-507500aFast decay of the velocity autocorrelation function in dense shear flow of inelastic hard spheres0 aFast decay of the velocity autocorrelation function in dense she a17, AVE DU HOGGAR, PA COURTABOEUF, BP 112, F-91944 LES ULIS CEDEX A, FRANCEbEDP SCIENCES S AcDEC a640030 v843 a

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

1 aOrpe, Ashish, V.1 aKumaran, V.1 aReddy, Anki1 aKudrolli, Arshad uhttps://library.ncl.res.in/content/fast-decay-velocity-autocorrelation-function-dense-shear-flow-inelastic-hard-spheres-001839nas a2200169 4500008004100000022001400041245007800055210006900133260007900202300001100281490000700292520120000299100002301499700002101522700002101543856010501564 2009 eng d a1539-375500aPhysical test of a particle simulation model in a sheared granular system0 aPhysical test of a particle simulation model in a sheared granul aONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USAbAMER PHYSICAL SOCcSEP a0313050 v803 a

We report a detailed comparison of a slow gravity-driven sheared granular flow with a discrete-element simulation performed in the same geometry. In the experiments, grains flow inside a silo with a rectangular cross section and are sheared by a rough boundary on one side and smooth boundaries on the other sides. Individual grain position and motion are measured using a particle index-matching imaging technique where a fluorescent dye is added to the interstitial liquid which has the same refractive index as the glass beads. The simulations use a Cundall-Strack contact model between the grains using contact parameters that have been used in many other previous studies and ignore the hydrodynamic effects of the interstitial liquid. Computations are performed to understand the effect of particle coefficient of friction, elasticity, contact model, and polydispersity on mean flow properties. We then perform a detailed comparison of the particle fluctuation properties as measured by the displacement probability distribution function and the mean square displacement. All in all, our study suggests a high level of quantitative agreement between the simulations and experiments.

1 aRycroft, Chris, H.1 aOrpe, Ashish, V.1 aKudrolli, Arshad uhttps://library.ncl.res.in/content/physical-test-particle-simulation-model-sheared-granular-system-002525nas a2200289 4500008004100000020002200041022001400063245005200077210005200129260021600181300001200397490000900409520151800418653000801936653001401944653001301958653001901971653001101990653002302001100002102024700002302045700002502068700002002093700002002113700001602133856008602149 2010 eng d a978-0-7354-0772-5 a0094-243X00aShear induced diffusion in dense granular flows0 aShear induced diffusion in dense granular flows a2 Huntington Quadrangle, STE 1NO1, Melville, NY 11747-4501 USAbIUTAM; ISIMM; Italian Inst Higher Math; US Natl Sci Fdn; Reg Council Reggio Calabria; Prov Reggio Calabria; Mediterranean Univ Reggio CalabriacJUN a221-2290 v12273 a

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.

10aDEM10aDiffusion10agranular10aindex matching10aLAMMPS10alaser fluorescence1 aOrpe, Ashish, V.1 aRycroft, Chris, H.1 aKudrolli, Arshad, A.1 aGoddard, J., D.1 aJenkins, J., T.1 aGiovine, P. uhttps://library.ncl.res.in/content/shear-induced-diffusion-dense-granular-flows-001966nas a2200181 4500008004100000022001400041245005100055210005000106260010300156300001000259490000700269520135100276100001801627700002101645700001701666700001801683856008301701 2012 eng d a0295-507500aFlow-induced channelization in a porous medium0 aFlowinduced channelization in a porous medium a6 RUE DES FRERES LUMIERE, MULHOUSE, 68200, FRANCEbEPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETYcJUN a580030 v983 a

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

1 aMahadevan, A.1 aOrpe, Ashish, V.1 aKudrolli, A.1 aMahadevan, L. uhttps://library.ncl.res.in/content/flow-induced-channelization-porous-medium-001584nas a2200181 4500008004100000022001400041245008500055210006900140260007900209300001100288490000700299520091600306100002001222700001601242700001801258700002101276856010501297 2014 eng d a1539-375500aFlow of granular matter in a silo with multiple exit orifices: jamming to mixing0 aFlow of granular matter in a silo with multiple exit orifices ja aONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USAbAMER PHYSICAL SOCcDEC a0622060 v903 a

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.

1 aKamath, Sandesh1 aKunte, Amit1 aDoshi, Pankaj1 aOrpe, Ashish, V. uhttps://library.ncl.res.in/content/flow-granular-matter-silo-multiple-exit-orifices-jamming-mixing-001465nas a2200169 4500008004100000022001400041245007800055210006900133260007900202300001100281490000700292520083600299100001601135700001801151700002101169856010501190 2014 eng d a1539-375500aSpontaneous jamming and unjamming in a hopper with multiple exit orifices0 aSpontaneous jamming and unjamming in a hopper with multiple exit aONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USAbAMER PHYSICAL SOCcAUG a0202010 v903 a

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.

1 aKunte, Amit1 aDoshi, Pankaj1 aOrpe, Ashish, V. uhttps://library.ncl.res.in/content/spontaneous-jamming-and-unjamming-hopper-multiple-exit-orifices-001700nas a2200181 4500008004100000022001400041245007600055210006900131260008700200300001100287490000700298520102400305100002301329700002601352700001801378700002101396856010101417 2016 eng d a1070-663100aFingering instability of a suspension film spreading on a spinning disk0 aFingering instability of a suspension film spreading on a spinni a1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USAbAMER INST PHYSICScJUN a0633030 v283 a

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. [''Linear stability of particle-laden thin films,'' Eur. Phys. J.: Spec. Top. 166, 77 (2009)] and Balmforth et al. [''Surface tension driven fingering of a viscoplastic film,'' J. Non Newtonian Fluid Mech. 142, 143 (2007)]. Published by AIP Publishing.

1 aKulkarni, Mayuresh1 aSahoo, Subhadarshinee1 aDoshi, Pankaj1 aOrpe, Ashish, V. uhttps://library.ncl.res.in/content/fingering-instability-suspension-film-spreading-spinning-disk02384nas a2200169 4500008004100000245010300041210006900144260000800213300001400221490000700235520175800242100002102000700002102021700002002042700002202062856013002084 2016 eng d00aPassive microrheology in the effective time domain: analysing time dependent colloidal dispersions0 aPassive microrheology in the effective time domain analysing tim cAUG a8167-81760 v123 a

We studied the aging dynamics of an aqueous suspension of LAPONITE (R), a model time dependent soft glassy material, using a passive microrheology technique. This system is known to undergo physical aging during which its microstructure evolves progressively to explore lower free energy states. Optical microscopy is used to monitor the motion of micron-sized tracer probes embedded in a sample kept between two glass plates. The mean square displacements (MSD) obtained from the motion of the tracer particles show a systematic change from a purely diffusive behavior at short aging times to a subdiffusive behavior as the material ages. Interestingly, the MSDs at all the aging times as well as different LAPONITE (R) concentrations superpose remarkably to show a time-aging time master curve when the system is transformed from the real time domain to the effective time domain, which is obtained by rescaling the material clock to account for the age dependent relaxation time. The transformation of the master curve from the effective time domain to the real time domain leads to the prediction of the MSD in real time over a span of 5 decades when the measured data at individual aging times are only over 2 decades. Since the MSD obtained from microrheology is proportional to the creep compliance of a material, by using the Boltzmann superposition principle along with the convolution relation in the effective time domain, we predict the stress relaxation behavior of the system in real time. This work shows that the effective time approach applied to microrheology facilitates the prediction of long time creep and relaxation dynamics of a time dependent soft material by carrying out short time experiments at different aging times.

1 aVyas, Bhavna, M.1 aOrpe, Ashish, V.1 aKaushal, Manish1 aJoshi, Yogesh, M. uhttps://library.ncl.res.in/content/passive-microrheology-effective-time-domain-analysing-time-dependent-colloidal-dispersions02064nas a2200169 4500008004100000022001400041245006900055210006900124260000800193300001100201490000700212520151400219100002601733700002101759700001801780856009601798 2018 eng d a1070-663100aSpreading dynamics of superposed liquid drops on a spinning disk0 aSpreading dynamics of superposed liquid drops on a spinning disk cJAN a0121100 v303 a

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.

1 aSahoo, Subhadarshinee1 aOrpe, Ashish, V.1 aDoshi, Pankaj uhttps://library.ncl.res.in/content/spreading-dynamics-superposed-liquid-drops-spinning-disk01883nas a2200157 4500008004100000022001400041245008800055210006900143260000900212300001100221490000800232520133300240100002101573700001801594856011301612 2019 eng d a2470-004500aFriction-mediated flow and jamming in a two-dimensional silo with two exit orifices0 aFrictionmediated flow and jamming in a twodimensional silo with  cJUL  a0129010 v1003 a

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.

1 aOrpe, Ashish, V.1 aDoshi, Pankaj uhttps://library.ncl.res.in/content/friction-mediated-flow-and-jamming-two-dimensional-silo-two-exit-orifices02272nas a2200253 4500008004100000022001400041245006300055210006300118260000800181300001200189490000700201520153700208653002001745653001501765653000801780653001901788653001301807653001701820100002101837700002301858700002101881700002101902856009501923 2020 eng d a0035-451100aMicrostructure and yielding of capillary force induced gel0 aMicrostructure and yielding of capillary force induced gel cMAY a291-3060 v593 a

We have investigated the rheology and structure of a gel formed from a mixture of non-Brownian particles and two immiscible liquids. The suspension of particles in a liquid undergoes gelation upon the addition of a small content of second, wetting liquid which forms liquid bridges between particles leading to a sample spanning network. The rheology of this gel primarily exhibits a yield stress at low shear rates followed by a linear variation of shear stress at high shear rates. The apparent yield stress extracted from the flow curves increases rapidly with volume fraction of the second liquid before saturation, while it exhibits a monotonic increase with increasing particle concentration. Rescaling of the yield stress curves using suitable shift factors results in an empirical expression for the yield stress showing squared dependence on liquid fraction and a rapid increase with particle fraction above a certain value, both combined in a highly non-linear manner. The microstructural variations with changing secondary liquid content and particle fractions are captured using three-dimensional X-ray tomography technique. The microstructure is observed to show increased local compactness with increased liquid content and increased spatial homogeneity with increased particle fractions. The images from X-ray tomography are analysed to obtain the distributions of particle-particle bonds (coordination number) in the system which serve to explain the observed yield stress behaviour in a qualitative manner.

10aCapillary force10aFlow curve10agel10aMicrostructure10aRheology10aYield stress1 aHuprikar, Sameer1 aUsgaonkar, Saurabh1 aLele, Ashish, K.1 aOrpe, Ashish, V. uhttps://library.ncl.res.in/content/microstructure-and-yielding-capillary-force-induced-gel01642nas a2200145 4500008004100000245006900041210006900110260000800179490000700187520112800194100002501322700002101347700002701368856010101395 2021 eng d00aSlip behavior during pressure driven flow of Laponite suspension0 aSlip behavior during pressure driven flow of Laponite suspension cMAY0 v333 a

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.

1 aKamdi, Prophesar, M.1 aOrpe, Ashish, V.1 aKumaraswamy, Guruswamy uhttps://library.ncl.res.in/content/slip-behavior-during-pressure-driven-flow-laponite-suspension01438nas a2200157 4500008004100000022001400041245006700055210006700122260000800189490000700197520092500204100002301129700001801152700002101170856008901191 2024 eng d a1070-663100aFlow and clogging behavior of a mixture of particles in a silo0 aFlow and clogging behavior of a mixture of particles in a silo cMAY0 v363 a

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.

1 aBhure, Sukhada, C.1 aDoshi, Pankaj1 aOrpe, Ashish, V. uhttps://library.ncl.res.in/content/flow-and-clogging-behavior-mixture-particles-silo01728nas a2200157 4500008004100000022001400041245007000055210006900125260000800194300001100202490000700213520120100220100002601421700002101447856010201468 2026 eng d a1070-663100aSurface coating induced lubrication in flowing granular materials0 aSurface coating induced lubrication in flowing granular material cAPR a0433320 v383 a

We investigate the flow of spherical, bulk granular particles down an inclined plane mixed with small-sized spherical lubricant particles using discrete element method simulations. Predefined cohesive interaction is implemented between lubricant and bulk particles, enabling the coating of the former over the latter. The overall flow rate exhibits non-monotonic dependence on lubricant content. Initially, it increases with lubricant addition, reaches a maximum at an intermediate lubricant content, and decreases for even higher lubricant content. The increase in the flow rate is attributed to a lower inter-particle friction coefficient between lubricant-coated bulk particles. The decrease in the flow rate at higher lubricant content, on the other hand, is attributed to enhanced densification and increased damping between crowded particles. Both these occurrences are examined using various flow level characteristics. The simulation results are found to be in qualitative agreement with previous experimental results. Overall, the outcome integrates novel computational insights and prior experimental results to enhance the understanding of the powder lubrication phenomena.

1 aChaudhary, Sayali, V.1 aOrpe, Ashish, V. uhttps://library.ncl.res.in/content/surface-coating-induced-lubrication-flowing-granular-materials