Elisabeth Guazzelli (Université de Paris)

Part I: Sedimentation of particles

Sedimentation of particles is ubiquitous in natural phenomena such as mud sedimentation in rivers and estuaries and rain drop sedimentation in the atmosphere. It is also a basic engineering technique of separation or clarification used in particular in the water treatment process for removing suspended solids from water. While it can be considered as one of the simplest suspension flows, much remains to be understood. The key difficulty lies in the long-range nature of the multi-body hydrodynamic interactions between the particles which leads to a complex and collective dynamics. This will be illustrated for sedimenting suspensions of spheres, of non-spherical particles such as fibers, and for sedimenting clouds of particles.

References:
[1] E. Guazzelli and E. J. Hinch. Fluctuations and instability in sedimentation. Annu. Rev. Fluid Mech. 498(43):97-116, 2011.
[2] E. Guazzelli and J. F. Morris. A physical introduction to suspension dynamics. Cambridge Texts in Applied Mathematics, CUP, 2012.

See slides and record.

Part II: Rheology of granular suspensions

Suspensions are composed of mixtures of particles and fluid and are omnipresent in industrial processes (e.g. waste disposal, concrete, drilling muds, metalworking chip transport, and food processing) and in natural phenomena (e.g. flows of slurries, debris, and lava). There are multiple avenues to study suspension rheology that will be introduced. Suspensions can be seen as a fluid with effective rheological properties but also as a two-phase system wherein the fluid and particles can experience relative motion. They can be described with constitutive laws in which the control parameter is the normal stress imposed to the particle phase rather than the volume fraction. This alternative description inspired by the frictional approach of dry granular media is particularly suited to yield examination of the rheology close to the jamming transition. Finally, beyond the classical problem of dense suspensions of hard spheres in a Newtonian fluid, there are entirely novel avenues of study concerning more complex mixtures of particles and fluid.

References:
[2] E. Guazzelli and J. F. Morris. A physical introduction to suspension dynamics. Cambridge Texts in Applied Mathematics, CUP, 2012.
[3] E. Guazzelli and O. Pouliquen. Rheology of dense granular suspensions. J. Fluid Mech. 852:35-73, 2018.

See slides and record.