Squishy Physics Seminars

Grain and Drain: Pattern Formation and Magnetic Manipulation in Granular Flows

Louison Thorens

Dec 6, 2023
6:00 pm to 7:00 pm | Pierce Hall, 209


Many natural and industrial processes rely on the displacement of mixed liquid, gas, and granular materials through confining structures. Specifically, such multi-phase flows through porous geometries play an essential role in engineering applications ranging from oil recovery and CO2 sequestration to filtration. Despite their tremendous potential economic and environmental impact, understanding these three-phase flows remains a formidable challenge. First, we study the formation of granular plugs during the slow drainage of a liquid-grain mixture in a tube illustrating the onset of a “bulldozing” instability. We define a new unstable regime leading to the periodic formation of dunes, analogous to the road “washboarding” instability, where a key element is the strong increase of the frictional forces with the angle of attack of the pushing meniscus at the liquid/air interface. Second, we develop an original method to control the frictional interactions at the origin of this bulldozing instability, by using ferromagnetic particles: submitted to a magnetic field, they acquire a magnetic moment, leading to tunable interactions of pairs of magnetic dipoles. We demonstrate the emergence of a radial force along the walls of the container, whose amplitude and direction are determined by the applied magnetic field. This "magnetic Janssen effect" allows us to control the apparent mass of a granular column, paving the way towards the design of granular meta-materials, for which mechanical (un)jamming properties can be remotely controlled or even programmed.

Speaker Bio

Louison Thorens obtained his master’s degree in physics from the Ecole Normale Supérieure de Lyon in France, followed by a Ph.D. achieved through a collaborative effort between PoreLab at the University of Oslo in Norway and the Ecole Normale Supérieure de Lyon in France. My doctoral research focused on magnetic granular materials and flow in porous media, which serves as the basis of this talk. I am currently a postdoctoral researcher at Tufts University working with Jeffrey Guasto, my research now primarily explores polymer dynamics and stretching within microfluidic flows.


Thomas Litschel, Bobby Haney, Yujing Du


Yujing Du