Forces and flow induced by a moving intruder in a granular packing: coarse-graining and DEM simulations versus experimen
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ORIGINAL PAPER
Forces and flow induced by a moving intruder in a granular packing: coarse‑graining and DEM simulations versus experiments Julien Lehuen1,2 · Jean‑Yves Delenne2 · Agnès Duri2 · Thierry Ruiz1 Received: 23 April 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The study of stress transmission and particles’ mobility in powder beds constitutes a challenging issue to improve processes such as milling, agglomeration and kneading. In this paper the ability to promote particle mobilities by means of an intruder is investigated. An experimental setup was developed to characterize the particles’ mobility at the voxel scale. A particle image velocimetry (PIV) algorithm was employed to determine the velocity fields in the vicinity of an intruder in ascendant vertical motion. A discrete element method model was developed to simulate the same system at the particle scale. Velocity maps were determined relying on a coarse-graining procedure and compared to PIV results. During the rise of the intruder the experimental and simulated drag forces are in good agreement. Spatio-temporal correlation between the granular mobility and the state of the force network are analyzed as a function of the height of the intruder. The drag force profile exhibits a relaxation trend, noised by fluctuations whose origin are in successive loading/rupture events. An interpretation of these fluctuations is proposed with regard to the development of preferential paths in the normal force network, and to the localization of sliding at the contacts scale. Finally, we show that global strains are a consequence of the ejection of particles directly in contact with the ends of the intruder. Keywords Intruder · Granular bed · Drag force · Particle image velocimetry (PIV) · Discrete element method (DEM) · Coarse graining
1 Introduction Mixing powders using intruders, such as blades, paddles, agitators… is widely used in chemical engineering [1, 2], civil engineering [3], pharmaceutical [4, 5], food science [6, 7] or agronomy [8, 9]. Common concerns regarding interactions between an intruder and a granular bed are shared by many unit operations like blending, kneading [10], wet agglomeration [11, 12] or milling [13, 14].
This article is part of the Topical Collection: Flow regimes and phase transitions in granular matter: multiscale modeling from micromechanics to continuum. * Julien Lehuen [email protected] 1
QualiSud, Univ Montpellier, CIRAD, Montpellier SupAgro, Univ Avignon, Univ La Réunion, Montpellier, France
IATE, Univ Montpellier, CIRAD, INRA, Montpellier SupAgro, Montpellier, France
2
More precisely, in blending operations, the paddle transmits mechanical energy to the granular bed inside a vessel [15]. To control the input energy or the shear rate, a range of low to high blenders are available. The efficiency of shear transmission requires adapted design of the whole setup (paddle shape and trajectory, vessel, wall-paddle gap) [16, 17]. One major issue is to transfer energy from the sca
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