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Soutenance de Lauren Rose

Foam flow in a confined inhomogeneous medium
When Jul 01, 2022
from 02:00 to 04:00
Where Salle des thèses
Contact Name Lauren Rose
Attendees Lauren Rose
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We present an experimental study of a 2D foam, composed of a single monolayer of bubbles, forced to flow in a confining Hele-Shaw cell, which models an open fracture. A defect localized in the center of the cell, increasing or decreasing locally its gap, strongly disturbs the foam flow. The transparency of the cell allows to directly observe and monitor the bubbles’ motion and deformation. We therefore performed a systematic study of the average bubble velocity and deformation fields, as well as the spatial distribution of the bubble rearrangements, as a function of the control parameters of the experiments: the imposed driving velocity, the cell and defect geometry (gap and height), as well as the bubble size and liquid foam fraction (controlling the foam rheology). For a localized constriction, we observe a strong fore-aft asymmetry of the velocity field, with an extended region downstream, where the foam velocity is much larger than the imposed driving one. We confirm here the elastic origin of such "overshoot" » or "negative-wake", typical of viscoelastic fluid flows around an obstacle. We also show a linear correlation between longitudinal profiles of velocity and deformation in the regions far from the obstacle, both upstream (where the foam is loaded elastically) and downstream (where it relaxes). We furthermore show the importance of the friction against the wall plates for strong confinement and/or flow rates, leading to positive wakes after a local increase of the gap cell, coupled with a transversal orientation of the bubbles, as well as to strong unusual bubbles distortions. In addition, we quantify the defect permeability, by computing the evolution of the bubble velocity within the defect as a function of its height. Finally, in a complementary study, within an international collaboration, we have investigated the interfacial dynamics of a simple fluid, forced to flow through a local partial obstacle in a confining cell. We show that the two-phase interface displacements are strongly affected by the imposed flow rate, leading to asymmetric imbibition–drainage hysteresis cycles.