Buoyant convection in a porous medium with an inclined permeability jump: An experimental investigation of filling box-type flows

Employing the concept of a ‘filling-box’ model, we report upon experiments featuring a dense, Boussinesq plume falling through a two-layered porous medium characterized by a high permeability upper layer and a low permeability lower layer. Upon striking the permeability jump, the plume fluid bifurcates leading to the formation of a pair of (up- and downdip) ‘primary’ gravity currents. The associated early time spreading behavior has been investigated in our previous work (Bharath et.al, JFM, vol. 902, 2020). It was shown that the primary gravity currents reach a state of runout wherein the inflow from the plume is precisely matched by the outflow due to draining. As an extension of our previous work, we herein examine the flow evolution over longer times and thereby study the impact of the lower layer depth. To this end, we characterize the formation of `secondary’ gravity currents, which form when the fluid draining from the underside of the gravity currents strikes the bottom (impermeable) boundary. As a consequence of the propagation of these secondary gravity currents, the primary gravity currents may become remobilized. Later, the gravity currents flow become impeded by the vertical sidewall boundaries, allowing us to categorize two qualitatively different filling regimes.