Rectilinear flow of non-colloidal suspensions: From interfacial fingers to particle plumes

It is known that non-colloidal spherical particles suspended in a viscous oil can induce viscous fingering when invading air inside a Hele-Shaw cell. Termed particle-induced viscous fingering (PIVF), this counterintuitive instability is driven by the accumulation of particles near the advancing air-suspension interface. PIVF involves two concurrent pattern formations: interfacial fingers and the emergence of dense particle plumes within the suspension. These patterns are intertwined, yet their coupling has remained an open question. Notably, existing studies of PIVF are limited to a radial geometry, which lessens this potential coupling due to the nature of the continuously expanding flow. To address this gap, we experimentally displace air with a particle suspension inside a rectilinear channel, which gives rise to new regimes of PIVF, including the merging and shedding of particle plumes. In this talk, we quantitatively characterize the emergent patterns and discuss the physical mechanism behind the formation and evolution of plumes coupled to the interfacial deformations.