Morphodynamics during air injection into a confined granular suspension

We study the injection of air into a granular suspension in a confined geometry. The grains and the suspending fluid are density matched allowing to vary the grain fraction ϕϕ over the whole range accessible: from ϕ=0ϕ=0 up to close to the maximum packing fraction ϕ∼60%ϕ∼60%. In this situation, a large variety of patterns is observed, that we link directly to the rheology of the suspension in the confined geometry. For low grain fractions ϕ<50%ϕ<50%, we show that taking into account an effective viscosity for the suspension flow, resulting from particle migration, allows to link quantitatively the observed structures to the classical Saffman–Taylor selection mechanism. For higher grain fractions ϕ>55%ϕ>55% the granular matrix is jammed and we deal with a weak porous medium. In this case we link the observed patterns to the reorganization occurring in the porous medium as a consequence of the injection process.