Flow between soft boundaries: fracture propagation and atomization

Fluid flows can generate stresses sufficiently large to destabilize interfaces, deform and fracture solid substrates. The deformation of the solid substrate is often considered to be in the linear elastic regime. And while the interactions between fluid flow and surface deformation are typically studied with a single fluid, two-phase flows are common in agricultural, manufacturing, and energy processes. In this talk, I will present two recent studies on flows confined by deformable, soft boundaries that can rupture and fracture.

First, we will consider the propagation of a liquid-filled fracture. The injection of the fluid in a brittle elastic material drives the formation and growth of a penny-shape fracture. Using model experiments, we characterize the fracture dynamics. The viscous dissipation in the fluid, the elastic stresses and toughness of the matrix control the flow in the fluid-filled fracture. We demonstrate that the propagation, during and after injection depends on the regime of fracture propagation, fluid-controlled vs matrix-controlled.

Then, I will present results on the atomization of oil in water emulsions. We study the impact of a drop of emulsion on a small target which leads to the formation and atomization of a liquid sheet. Here the dispersed phase is confined between air/liquid interfaces. The oil droplets modify the dynamics of an aqueous liquid sheet and its break-up into droplets. As the viscosity of the oil phase decreases and the surface tension difference between the phases increases, the liquid sheet becomes more unstable, and holes are primarily responsible for the atomization of the sheet.

These studies illustrate the complex couplings between multiphase flows and substrate deformation.