"Granular materials and suspensions" is a traditional and strong research interest in our laboratory. Our approach is mostly experimental. The main themes developed here concern natural flows (avalanches, erosion, dunes or craters formation) and industrial flows (transport in pipes, stress distributions in confined media).
Gardner transition in a granular glass
Analyzing the dynamics of a vibrated bidimensional packing of bidisperse granular disks below jamming, we provide evidence of a Gardner phase deep into the glass phase. To do so, we perform several compression cycles within a given realization of the same glass and show that the particles select different average vibrational positions at each cycle, while the neighborhood structure remains unchanged. The separation between the cages obtained for different compression cycles plateaus with an increasing packing fraction, while the mean square displacement steadily decreases.
Stresses in a sheared suspension
In a suspension of non-Brownian beads suspended in a very thick fluid, shear-induced agitation induces a particle-phase stress analogous to osmotic pressure or dilatency mixing in granular media.
Propulsion in the vicinity of a granular media
We are interested in the particles resuspension by some flatfish, as soles or lines, capable of generating a flow allowing resuspension of sand to bury and avoid predators. Beating fins with oscillating movements, these fish create vortices that raise the sand and deposit them on their back. Here, a rigid or flexible disk is placed on top of a granular bed to mimic the movement of the fins.
Local rheology in the granular flow around an intruder
The rheological properties of granular matter within a two-dimensional flow around a moving disk is investigated experimentally. The strain and stress tensors are estimated at the grain scale in the time-averaged flow field around a large disk pulled at constant velocity.
Destabilization of an immersed granular bed by thermal convection
If the resuspension of a granular bed by fluid flows (vortices or shear flows) has been the subject of many studies, the ability to fluidize particles with a vertical gradient of temperature remains poorly understood. A localized heat source under a granular bed shows a strong entrainment of grains, occuring beyond a temperature threshold through the generation of particle-laden plumes.
Nonlinear mechanic of fragile granular packing
Jamming occurs when a system develops a yield stress—behaves as a solid—in a disordered state. Granular matter belongs to these system and have this transition. We experimentally probe the mechanical response in the vicinity of this transition with local measures of the stress state and strain state of the granular packing.
Scour around a bridge pier
Sediment erosion and transport phenomena may represent a significant threat to human activities, infrastructure and ecosystems. For example, around a bridge pier or offshore platform, erosion can damage the structure and cause its collapse. Despite the risks, a physical description of the erosion phenomenon in the vicinity of structures remains incomplete to this day, especially the coupling between fluid dynamics and transport of solid particles is not well quantified. We study this phenomenon to characterize the particle dynamics in the presence of a flow in the vicinity of one or more immersed obstacle(s).
Displacement in sand
The displacement of an object in a granular medium induces a reorganization of the grains. We study by images correlations (PIV) both the velocity field of grain and its fluctuations as well as the force required to move the object in such environment. A hydrodynamic description of granular material can account for the main observations.
Erosion of an immersed granular bed by an liquid jet
Description is coming soon.
Tsunami generation by granular collapse
Landslides or cliff collapse can generate tsunamis that can lead to serious damage to coastlines and major risks for neighboring populations. A quasi two-dimensional experiment is used to study the generation of the waves produced by a granular collapse in a fluid layer (here in green). The influence of the grains (size, shape, etc.) and the water depth on the wave produced is studied by image analysis.