Fragmentation versus Cohesion

Two-layer thermally driven turbulence: mechanisms for interface breakup

“…Liquid can break up or fragment in multiphase turbulence (Deane & Stokes 2002;Villermaux 2007;Wang, Mathai & Sun 2019;Villermaux 2020). This physical phenomenon is very important for raindrops (Josserand & Zaleski 2003;Villermaux & Bossa 2009), for ocean waves and the resulting spray (Veron 2015), and even for the transmission of virus-laden droplets during coughing or sneezing (Bourouiba 2020;Chong et al 2021).…”

Polymer scission in turbulent flows

“…Unlike the fragmentation of liquid jets, sheets, or drops (Villermaux 2007, 2020), the modelling of flow-driven scission in turbulent polymer solutions is still in its infancy (Soares 2020). The reason for this has to be sought in the difficulty of including the microscopic details of the scission process in constitutive models of polymer solutions.…”

Stretching and break-up of saliva filaments during speech: A route for pathogen aerosolization and its potential mitigation

“…Over many decades fluid mechanicians have looked at droplets formed in a plethora of situations [32,33] and, more recently, fragmentation of sneeze ejecta have been described [34], where large mucus ligaments of several millimeters in diameter lead to large sneeze drops. But the literature of airborne asymptomatic transmission during speech has only indirectly considered two mechanisms [4,6]: (1) bursting of films in the lungs where respiratory passages are blocked during cycles of exhalation and inhalation, which is the so-called bronchial fluid film burst hypothesis [4,35], though, in fact, the authors only measure the final droplet sizes, as do many other researchers [3,36], and (2) theoretical descriptions of shear-induced, airflow-driven instabilities of the mucus fluids lining the respiratory paths [37].…”

“…The relation of the final film thickness, prior to destabilization to form filaments, depends on the initial liquid volume of saliva, its rheology, including possible Marangoni effects [33] and material inhomogeneities, and the stretching rate; this is an interesting and challenging problem for future research. For instance, in the Supplemental Material (see Movie S13) we report a model experiment rapidly pulling a saliva film between two cylindrical plastic tubes, representing the lips: during the stretching, in some cases, we are able to visualize hole formation in the sheets, which is the precursor of filament formation (also seen in the movie), and in each of those cases nucleation occurred at the boundary.…”