Stannarius, R. (Ralf)
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- Continuously heated granular gas of elongated particles(2021) Harth, K. (Kirsten); Stannarius, R. (Ralf); Puzyrev, D. (Dmitry); Pongó, T. (Tivadar); Cruz-Hidalgo, R. (Raúl)Some years ago, Harth et al. experimentally explored the steady state dynamics of a heated granular gas of rod-like particles in microgravity [K. Harth et al. Phys. Rev. Lett. 110, 144102 (2013)]. Here, we report numerical results that quantitatively reproduce their experimental findings and provide additional insight into the process. A system of sphero-cylinders is heated by the vibration of three flat side walls, resulting in one symmetrically heated direction, one non-symmetrically heated direction, and one non-heated direction.
- Flow in an hourglass: particle friction and stiffness matter(2021) Stiga, V. (Viktória); Stannarius, R. (Ralf); Pongó, T. (Tivadar); Cruz-Hidalgo, R. (Raúl); Torok, J. (János); Szabó, B. (B.); Lévay, S. (Sára); Börzsönyi, T. (Tamás)Granular flow out of a silo is studied experimentally and numerically. The time evolution of the discharge rate as well as the normal force (apparent weight) at the bottom of the container is monitored. We show that particle stiffness has a strong effect on the qualitative features of silo discharge. For deformable grains with a Young modulus of about Ym ¿ 40 kPa in a silo with basal pressure of the order of 4 kPa, lowering the friction coefficient leads to a gradual change in the discharge curve: the flow rate becomes filling height dependent, it decreases during the discharge process. For hard grains with a Young modulus of about Ym ¿ 500 MPa the flow rate is much less sensitive to the value of the friction coefficient. Using DEM data combined with a coarse-graining methodology allows us to compute all the relevant macroscopic fields, namely, linear momentum, density and stress tensors. The observed difference in the discharge in the low friction limit is connected to a strong difference in the pressure field: while for hard grains Janssen-screening is effective, leading to high vertical stress near the silo wall and small pressure above the orifice region, for deformable grains the pressure above the orifice is larger and gradually decreases during the discharge process. We have analyzed the momentum balance in the region of the orifice (near the location of the outlet) for the case of soft particles with low friction coefficient, and proposed a phenomenological...
- Cluster dynamics in dense granular gases of rod-like particles(2021) Harth, K. (Kirsten); Trittel, T. (Torsten); Fischer, D. (David); Stannarius, R. (Ralf); Puzyrev, D. (Dmitry); Cruz-Hidalgo, R. (Raúl)Granular gases are interesting multiparticle systems which, irrespective of the apparent simplicity of particle interactions, exhibit a rich scenario of so far only little understood features. We have numerically investigated a dense granular gas composed of frictional spherocylinders which are excited mechanically by lateral vibrating container walls. This study was stimulated by experiments in microgravity on parabolic flights. The formation of spatial inhomogeneities (clusters) was observed in a region near the corners of the container, about halfway from the excitation plates. The particles in the clusters show a tendency to align parallel to the container walls, seemingly increasing the stabilizing effect of friction. The simulation results provide hints that the phase difference of the vibrations of the two excitation walls might affect the cluster dynamics.
- Silo discharge of mixtures of soft and rigid grains(2021) Harth, K. (Kirsten); Trittel, T. (Torsten); Wang, J. (Jing); Stannarius, R. (Ralf); Pongó, T. (Tivadar); Cruz-Hidalgo, R. (Raúl); Illig, M. (Maja); Fan, B. (Bo); Börzsönyi, T. (Tamás)We study the outflow dynamics and clogging phenomena of mixtures of soft, elastic low-friction spherical grains and hard frictional spheres of similar size in a quasi-two-dimensional (2D) silo with narrow orifice at the bottom. Previous work has demonstrated the crucial influence of elasticity and friction on silo discharge. We show that the addition of small amounts, even as low as 5%, of hard grains to an ensemble of soft, low-friction grains already has significant consequences. The mixtures allow a direct comparison of the probabilities of the different types of particles to clog the orifice. We analyze these probabilities for the hard, frictional and the soft, slippery grains on the basis of their participation in the blocking arches, and compare outflow velocities and durations of non-permanent clogs for different compositions of the mixtures. Experimental results are compared with numerical simulations. The latter strongly suggest a significant influence of the inter-species particle friction.
- An instrument for studying granular media in low-gravity environment(American Institute of Physics, 2018) Pöschel, T. (T.); Falcon, E. (Eric); Yu, P. (P.); Palencia, F. (F.); Fischer, D. (David); Luding, S. (S.); Fauve, S. (S.); Clement, E. (E.); Garrabos, Y. (Y.); Schockmel, J. (J.); Lecoutre, C. (C.); Stannarius, R. (Ralf); Opsomer, E. (E.); Hou, M. (M.); Cazaubiel, A. (A.); Noirhomme, M. (M.); Crassous, J. (Jérome); NO USAR Maza, D. (D.); Aumaitre, S. (S.); Montero, Á. (Ángel); Jia, X. (X.); Vandewalle, N. (N.); Sperl, M. (M.); Behringer, R.P. (R. P.); Durian, D.J. (D. J.)A new experimental facility has been designed and constructed to study driven granular media in a lowgravity environment. This versatile instrument, fully automatized, with a modular design based on several interchangeable experimental cells, allows to investigate research topics ranging from dilute to dense regimes of granular media such as granular gas, segregation, convection, sound propagation, jamming and rheology - all without the disturbance by gravitational stresses active on Earth. Here, we present the main parameters, protocols and performance characteristics of the instrument. The current scientific objectives are then briefly described and, as a proof of concept, some first selected results obtained in low gravity during parabolic flight campaigns are presented.
- Linking bottleneck clogging with flow kinematics in granular materials: the role of silo width(2017) Zuriguel-Ballaz, I. (Iker); Stannarius, R. (Ralf); Ashour, A. (Ahmed); Arevalo, R. (Roberto); Maza-Ozcoidi, D. (Diego); Gella, D. (Diego)We demonstrate experimentally that clogging in a silo correlates with some features of the particle velocities in the outlet proximities. This finding, that links the formation of clogs with a kinematic property of the system, is obtained by looking at the effect that the position of the lateral walls of the silo has on the flow and clogging behavior. Surprisingly, the avalanche size depends nonmonotonically on the distance of the outlet from the lateral walls. Apart from evidencing the relevance of a parameter that has been traditionally overlooked in bottleneck flow, this nonmonotonicity supposes a benchmark with which to explore the correlation of clogging probability with different variables within the system. Among these, we find that the velocity of the particles above the outlet and their fluctuations seem to be behind the nonmonotonicity in the avalanche size versus wall distance curve.
- The role of the particle aspect ratio in the discharge of a narrow silo(2022) Stannarius, R. (Ralf); Pongó, T. (Tivadar); Cruz-Hidalgo, R. (Raúl); Torok, J. (János); Fan, B. (Bo); Hernández-Delfín, D. (Dariel); Börzsönyi, T. (Tamás)The time evolution of silo discharge is investigated for different granular materials made of spherical or elongated grains in laboratory experiments and with discrete element model (DEM) calculations. For spherical grains, we confirm the widely known typical behavior with constant discharge rate (except for initial and final transients). For elongated particles with aspect ratios between 2 < L/d < 6.1, we find a peculiar flow rate increase for larger orifices before the end of the discharge process. While the flow field is practically homogeneous for spherical grains, it has strong gradients for elongated particles with a fast-flowing region in the middle of the silo surrounded by a stagnant zone. For large enough orifice sizes, the flow rate increase is connected with a suppression of the stagnant zone, resulting in an increase in both the packing fraction and flow velocity near the silo outlet within a certain parameter range.