Trapping and escape of viscous fingers in a soft Hele-Shaw cell

Abstract

We study viscous fingering instability in a soft Hele-Shaw cell, in which one of the walls is replaced by a bounded elastomer. For sufficiently high flow rates in our experiments, fingers can get trapped because the deforming solid contacts the opposite wall, sealing the cell near its rim, although in numerical simulations of axisymmetric bubble expansion at the same control parameters, the interface escapes. For parameter regimes in which narrower fingers grow, we find the opposite behavior: the cell seals in axisymmetric numerics but fingers escape the cell in experiments, suggesting that viscous fingering can either promote or suppress the choking of the cell.