SOFT-Complex Fluids & Solids

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Granular Media and Powders

This theme deals with the static and flow behaviors of granular media and cohesive powders, especially in the dense regime. A large effort has been devoted in the group over the last two decades to develop an hydrodynamic description of dense granular flows for idealized systems. We now extend this approach to more complex situations, such as the question of the forces exerted on solid objects immersed in grains, silo flows, flow of cohesive granular materials, powders compaction and the mechanics of entangled media like fibre bundles.

Research

Publications

Projects

Research

Rheology of Dense Granular Flows

Participants: Y. Forterre, B. Metzger, O. Pouliquen
Collaboration: B. Andreotti (PMMH), I. Einav (Sydney University), N. Vandenberghe (IRPHE), F. Guillard (Sydney University), society SAFE METAL, F. Bertails-Descoubes (INRIA Grenoble)
PhD/post-doc: P. Jop (PhD 2003-2006), A. Reddy (post-doc 2009-2010), F. Guillard (AMN 2010-2013), P. Rognon (post-doc, 2011-2012)

Most granular flows encountered in industry and geophysics occur in an intermediate regime between the ‘solid’ regime described in soil mechanics and the ‘gas’ regime described by the kinetic theory. In this ‘dense’ or ‘liquid’ regime, the concentration is large and both collision and enduring contacts are important making difficult the derivation of constitutive equations. Over the last two decades, we have contributed to the development of a continuous description of dense granular flows in terms of a visco-plastic frictional rheology. This approach provides a frist order description of many flow configurations but has also limitation, in particular for slow flows where nonlocal effects appear. We investigate these phenomena in simple geometries, such as flows down inclined planes, simple shear flow or Couette flow.

Granular Fluid/Structure Interaction

Participants: P. Aussillous, Y. Forterre, O. Pouliquen
Collaboration: N. Vandenberghe (IRPHE), F. Guillard (Sydney University), society SAFE METAL, F. Bertails-Descoubes (INRIA Grenoble)
PhD/post-doc: F. Guillard (AMN 2010-2013), J John Soundar Jerome (2013-2014, ANR CRASH/Labex), V. Paume (CIFRE 2020-),

Understanding the interaction between a granular flow and a solid object has applications ranging from industry (extraction and agriculture machines, locomotion of vehicules and inspection robots, balistics) to geophysics (impact cratering) to biology (animal locomotion in particulate soil, root anchoring and growth). We address this question using experiments, continuum modeling and discrete numerical simulations, in the light of the progress made on the rheology of granular flows. Investigation includes the drag and lift forces exerted on an object moving in a static granular materials, the force on large particles immersed in a granular flow in relation with particle size-segregation, the impact of a solid object on a dry or wet granular bed, the penetration of complex objects into a granular soil in relation with mining equipments.

Silo Flows

Participants: Pascale Aussillous, Blanche Dalloz
Collaborations: Université de Béchar (Algérie) – Institut de radioprotection et de Sûreté Nucléaire (IRSN), J-Y Lagrée and L. Staron (IJLRA), H. Capart (Taïwan)
PhD/Post-doc: Yixian Zhou (IRSN, 2013-2016), M. Benyamine (thèse de doctorat d’état), Z. Zou (IRSN, 2016-2019)

This subject was initiated in 2012 as part of a state thesis at the University of Béchar in Algeria. We experimentally studied the emptying of a silo containing a bidisperse mixture of grains, for two types of silos (rectangular and cylindrical, flat-bottomed). A simple physical model based on a mixing law was proposed and validated by discrete simulations. In collaboration with IRSN, we are now studying the dynamics of silo discharge when the grains are ejected by a pressurized gas using a combination of experiments and two-phase contiuum modeling in collaboration with the Institut d’Alembert and the experimental shock team of IUSTI.

Cohesive Powders

Participants: B. Dalloz, M. Nicolas, O. Pouliquen
Collaboration: P. Sornay, CEA, PY Lagrée (IJLRA), A. Sauret (CNRS/Santa-Barbara), Saint-Gobain/CREE Cavaillon
PhD/post-doc: A. Benedetti, J.-E. Mathonnet (PhD, CEA), A. Gens (PhD Ministère 2018-), S. Mandal (post-doc ANR, 2018-)

Characterization and prediction of the ‘flowability’ of powders are of paramount importance in many industries. However, our understanding of the flow of powders like cement or flour is sparse compared to the flow of (dry) granular media like sand. The main difficulty arises because of the presence of adhesive forces between the grains, preventing smooth and continuous flows. Several tests are used in industrial contexts to probe and quantify the ‘flowability’ of powders. However, they remain empirical and would benefit from a detailed study of the physics controlling the flow dynamics. We address the flow and compaction of powders using experiments on model cohesive granular materials and discrete numerical simulations. Several configuration are investigated, such as powder flows under vertical or horizontal vibrations, flow in silo, flow down inclined planes or granular collapse of cohesive medium.