The team "Granular materials and Suspensions" develops a mainly experimental work on the one hand on fundamental problems of rheology of these materials, on the other hand on natural or technological situations in which these materials are involved. The rheological studies concern both the dry grains for which the interactions are made by solid contacts and the suspensions of particles for which the interactions are also of a hydrodynamic nature via the carrier fluid. The influence of the interstitial fluid is, for example, important in the elementary process of collision between grains or grains with the walls, but also in the development of differences of normal stresses under shear or else in the phenomena of migration and particle structuring. Of particular interest is the study of dense regimes, close to the blocking transition or "jamming", separating a "fluid" state from a "solid" state.
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).
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.
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.
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.
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.
Structuration of a particle suspension oscillating in a Hele-Shaw cell
Time dependent motions of particle suspensions occur in many natural (e.g ;seabeds) and industrial flows. We have shown that the concentration of a suspension of non Brownian iso-dense particles oscillating between transparent parallel plates may vary spatially in the direction parallel to the flow, giving rising to periodic transverse streaks. The analysis of the particle distribution in the aperture of the cell shows that there is first a segregation of the particles into a plane layer in the center of the aperture which becomes wavy and, then, the periodic structure appears.
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.
Erosion of an immersed granular bed by an liquid jet
We are interested here in the erosion of a non-cohesive granular medium by a jet, circular or plane, in the laminar or turbulent regimes. After the fine characterization of the erosion threshold and crater morphology taking into account the complex hydrodynamics of the jet, we now carry out complementary measurements of the velocity field of the fluid and grains by PIV technique.