Axisymmetric gas-liquid displacement flow under a confined elastic slab

Abstract: A circular Hele-Shaw cell bounded by a volumetrically confined elastic solid can act as a fluidic fuse: during radially outward fluid flow, the solid deforms in response to the viscous pressure field such that the gap expands near the inlet (at the centre) and contracts near the outlet (around the rim). If the flow rate exceeds a critical value, the gap at the outlet can close completely, interrupting/choking the flow. Here, we consider the injection of gas into such a soft-walled Hele-Shaw cell filled with viscous liquid. Our theoretical model and numerical simulations for axisymmetric flow driven by the injection of an expanding gas bubble show that the bubble increases the critical flow rate of choking via two mechanisms. Firstly, as the interface approaches the rim, it reduces the length over which the viscous pressure gradient deforms the solid, which increases the critical flow rate above which choking occurs. Secondly, compression of the gas reduces the outlet flow rate relative to the inlet flow rate. As a consequence, for large injection rates, a near-choking regime is established in which the outlet flow rate becomes independent of the injection rate and instead depends only on the instantaneous position of the interface. Our travelling-wave model for the advancement of the bubble front will enable future reduced-order modelling of non-axisymmetric problems, such as viscous fingering.