Breakup morphology of expelled respiratory liquid: From the perspective of hydrodynamic instabilities

Abstract

Understanding the breakup morphology of an expelled respiratory liquid is an emerging interest in diverse fields to enhance the efficacious strategies to attenuate disease transmission. In this paper, we present the possible hydrodynamic instabilities associated with expelling the respiratory liquid by a human. For this purpose, we have performed experiments with a cylindrical soap film and air. The sequence of the chain of events was captured with high-speed imaging. We have identified three mechanisms, namely, Kelvin–Helmholtz (K–H) instability, Rayleigh–Taylor (R–T) instability, and Plateau–Rayleigh (P–R) instability, which are likely to occur in sequence. Furthermore, we discuss the multiple processes responsible for drop fragmentation. The processes such as breakup length, rupture, ligament, and drop formation are documented with a scaling factor. The breakup length scales with We −0.17 , and the number of ligaments scales as . In addition, the thickness of the ligaments scales as We −0.5 . Here, We and Bo represent the Weber and Bond numbers, respectively. It was also demonstrated that the flapping of the liquid sheet is the result of the K–H mechanism, and the ligaments formed on the edge of the rim appear due to the R–T mechanism, and finally, the hanging drop fragmentation is the result of the P–R instability. Our study highlights that the multiple instabilities play a significant role in determining the size of the droplets while expelling a respiratory liquid. This understanding is crucial to combat disease transmission through droplets.

The perspective of fluid flow behavior of respiratory droplets and aerosols through the facemasks in context of SARS-CoV-2

“…Vadivukkarasan et al 58 experimentally investigated the breakup morphology of expelled respiratory liquid. The expelled respiratory liquid sputum from a human was emulated using a soap film, and air and flow dynamics were visualized.…”

Reducing chances of COVID-19 infection by a cough cloud in a closed space

“…Given the interest in understanding the safe distance between persons and the utility of face masks during the pandemic, a number of experimental 6,12,13 and numerical 1,2,14 studies have recently been undertaken. For instance, results of a 3D computational model 1 suggested that at large wind speeds varying from 4 km/h to 15 km/h, the cloud could travel up to 6 m. Vadivukkarasan et al 15 identified three instabilities, Kelvin–Helmholtz, Rayleigh–Taylor, and Plateau–Rayleigh, occurring in sequence to be the mechanism responsible for the breakup of the expelled respiratory liquid into respiratory droplets. The role of different sized droplets in spreading the disease has been examined.…”

SARS COV-2 virus-laden droplets coughed from deep lungs: Numerical quantification in a single-path whole respiratory tract geometry

“…Instead, aerosol droplets were assumed to stochastically fill the alveolar airspaces before coughing, and the range of the droplet size followed the measurements of Johnson et al 11 and Bake et al 18 Respiratory aerosol generation can be a highly complex process governed by multiple hydrodynamic stabilities, as demonstrated by Vadivukkarasan et al , who experimentally studied the breakup morphology of an expelled respiratory fluid. 82 Mechanisms of endogenous aerosol generation include reopening of closed airways and shear-induced destabilization of air–liquid interface. 18 Specifically, small peripheral bronchioles can narrow or close after a deep exhalation; the reopening process at the start of the inhalation produces droplets.…”