, TORRES ULLOA, CARLOS ALEJANDRO, HERNANDEZ MONTELONGO, JESUS JACOBO, Paul Grassia, Paul S., Rajabi, Hamed, Torres-Ulloa, Carlos Alejandro, Hernández-Montelongo, Jacobo, Potter, J., Moston, J.

A two-dimensional foam staircase structure is considered with N bubbles stacked in a zigzag fashion along a channel. A model is analysed for determining the configuration of a staircase set into motion under the action of a high imposed driving pressure. Minimum and also maximum permitted bubble sizes for which the staircase structure survives are identified. Both minimum and maximum sizes are found to be decreasing functions of N. Behaviours in the limit of large N are identified, albeit tentatively, as the methodology for computing the staircase structure is found to be highly stiff. Indeed, as N increases, tiny changes in the staircase configuration at the downstream end lead to large geometric changes at the upstream end, limiting the domain of N values for which structures can be readily computed. © 2025 Elsevier B.V., All rights reserved.

, TORRES ULLOA, CARLOS ALEJANDRO, Paul Grassia, Paul S., Torres-Ulloa, Carlos Alejandro, Shokri, Nima, Aryana, Saman A.

The pressure-driven growth model is used to investigate the propagation of a foam front in a porous medium. Initially, the foam front moves forward due to an imposed gas injection pressure. Later, however, the injection pressure is reduced so that part of the front, deeper down in the medium, switches to reverse flow. The foam front is not, however, predicted to retrace its original path. Along most of its length moreover, the reverse flow front is predicted to move surprisingly quickly, which also affects the total area swept out. On the other hand, some parts of the front very close to the bottom move only slowly in reverse flow, such that the front is predicted to develop a kinked shape. Perturbations superposed on the front shape can also cause it to develop sharp concave corners. Overall, the findings enhance the understanding of foam behaviour in porous media, when sudden changes in flow direction occur during the course of the flow. © 2025 Elsevier B.V., All rights reserved.