Bags mediated film atomization in a cough machine

TL;DR

This study investigates how fluid mechanical processes, especially bag-like structures formed during shearing of a liquid film, contribute to bioaerosol generation in coughing, combining experiments and simulations to understand droplet formation.

Contribution

It introduces a novel experimental setup and numerical analysis to elucidate the role of bag-like structures and rim dynamics in aerosol formation during coughs.

Findings

Aerosol generation is mediated by inflated bag-like structures.

Breakup of bags is triggered by retracting holes puncturing the surface.

Fluid viscosity stabilizes the film, leading to smaller droplets.

Abstract

We combine experiments and numerical computations to examine underlying fluid mechanical processes associated with bioaerosol generation during violent respiratory manoeuvres, such as coughing or sneezing. Analogous experiments performed in a cough machine -- consisting of a strong shearing airflow over a thin liquid film, allow us to illustrate the changes in film topology as it disintegrates into small droplets. We identify that aerosol generation during the shearing of the liquid film is mediated by the formation of inflated bag-like structures. The breakup of these bags is triggered by the appearance of retracting holes that puncture the bag surface. Consequently, the cascade from inflated bags to droplets is primarily controlled by the dynamics and stability of liquid rims bounding these retracting holes. We also reveal the stabilizing role of fluid viscosity that eventually leads to the generation of smaller droplets.