Liquid plug formation in an airway closure model

The flow physics of COVID-19

“…Predicting the fragmentation and droplet size distribution resulting from this fragmentation is non-trivial because mucus is a viscoelastic shear-thinning fluid subject to surface tension. This enables multiple instabilities to bear on this problem (Malashenko, Tsuda & Haber 2009), including surface-tension-driven Rayleigh-Plateau instability (Eggers 1997;Lin & Reitz 1998;Romanò et al 2019), shear-driven Kelvin-Helmholtz instability (Kataoka, Ishii & Mishima 1983;Scardovelli & Zaleski 1999) and acceleration-driven Rayleigh-Taylor instability (Joseph, Beavers & Funada 2002;Halpern & Grotberg 2003). The Rayleigh-Taylor instability is particularly important in spasmodic events such as coughing and sneezing.…”

The effect of viscoelasticity in an airway closure model

“…However, several important insights in the airway closure phenomenon can still be disclosed by reproducing the whole closure phenomenon, including the formation of a stationary plug by bifrontal plug growth that has been recently shown to be potentially a major cause of epithelial cell damage in the entire air closure process (Romanò et al. 2019).…”

“…In our previous study (Romanò et al. 2019), we modelled the annular film coating the airway by means of a Newtonian fluid. The density and dynamic viscosity were assumed to be the weighted mean of the physical properties of mucus and periciliary liquid that form the multilayer liquid coating the airways.…”

Particle accumulation in high‐Prandtl‐number liquid bridges

“…For an accurate modeling, however, the only parameter ∆ of the collision model, depending on particle size, density and flow parameters, should be determined carefully [2]. To avoid estimating ∆, we employ a more physically-based PBI model which makes use of the lubrication-induced drag acting on the particle in direction normal to the boundary [4].…”