Pattern Formation in Suspension Flows
In this talk, we focus on two complementary flow configurations in which the presence of suspended particles drastically alters the dynamics of the fluid-fluid interface and leads to pattern formation. First, we observe a particle-induced fingering instability when a mixture of particles and viscous oil displaces air inside a 2D channel. Our experimental results show that the characteristics of fingering depend on the particle volume fraction and on the ratio of the particle diameter to gap size. A reduced model is also presented to rationalize the critical wavenumber of instability. In the second part of the talk, we discuss the result of injecting air into a packing of soft hydrogel beads that are saturated in water. We find that this new combination of buoyancy, capillarity, and elasticity under confinement leads to complex morphologies of air migration, as well as nontrivial dynamics in the amount of trapped air in the system.