A numerical cough machine

TL;DR

This paper presents a simplified physical model of coughing and sneezing, using advanced simulation techniques to analyze droplet size distributions and atomization mechanisms, aligning with experimental observations.

Contribution

It introduces a numerical model of coughing using Volume-Of-Fluid simulations with fine mesh adaptation, providing insights into droplet size distributions and atomization processes.

Findings

Droplet size distribution follows a $d^{-3.3}$ power law.

Simulation results agree with previous experimental re-analyses.

No evidence of bimodal droplet size distribution in the model.

Abstract

We introduce a simplified model of physiological coughing or sneezing, in the form of a thin liquid layer subject to a rapid (30 m/s) air stream. The setup is simulated using the Volume-Of-Fluid method with octree mesh adaptation, the latter allowing grid sizes small enough to capture the Kolmogorov length scale. The results confirm the trend to an intermediate distribution between a Log-Normal and a Pareto distribution $P(d) \propto d^{-3.3}$ for the distribution of droplet sizes in agreement with a previous re-analysis of experimental results by one of the authors. The mechanism of atomisation does not differ qualitatively from the multiphase mixing layer experiments and simulations. No mechanism for a bimodal distribution, also sometimes observed, is evidenced in these simulations.