Interfacial tension plays a crucial role in multiphase configurations as for fragmentation and Marangoni flows. Liquid jet fragmentation is of most use in applications like aerospace cryogenic engines, ocean sprays and farming irrigation. Marangoni flows, acting at the interface between phases, can raise from the presence of trace soluble surfactants and, in the context of Liquid Infused Surfaces, have heavily detrimental effects. Those two study cases will be the focus of my seminar so to explore interfacial tension effects. On the side of liquid jet fragmentation, modelling the droplet size distribution is a core interest. For agricultural-like jets, describing droplet fragmentation as a cascade process, similarly to the eddy cascade in turbulence as suggested by Novikov & Dommermuth (1997) for turbulent sprays, would appear relevant. However, this overlooks the experimental observations of the instabilities taking place along the liquid jet, that eventually create ligaments which in turn break up into droplets. This ligament-mediated break-up was accounted for in the statistical description derived by Villermaux (2004). I highlight how those theories complement each other for the description of DNS and experimental data and conclude on their field of application, with respect to the distance from the injection nozzle. Additionally, the joint distribution of the droplet size and velocity is shown to be self-similar across a large range of Weber number, when plotted in a properly normalised phase space. On the side of Marangoni flows induced by soluble surfactants, the interest is in modelling the mass transfer of surfactant between the phases, so to accurately describe the gradient of interfacial tension. Liquid Infused Surfaces, made of millimetric oil-filled grooves, are a promising technology for reducing friction and biofouling on ship hulls, but can be fully immobilised by adverse Marangoni flows in the presence of trace surfactant. By reformulating the model of Sundin & Bagheri (2022), several regimes can be defined for both the interfacial velocity and the surfactant mass transfer from the bulk to the liquid-liquid interface. The theoretical derivations also point towards a possible influence of rheological stresses on the interface dynamics. Finally, those physical considerations have practical consequences on the LIS design so to minimise adverse surfactant-induced Marangoni flows.
Accès Salle des séminaires FAST-LPTMS (Bât. 530, salle C.120, 1er)