ON THE EJECTION SCALE PROBLEM OF EXPIRATORY EVENTS FROM THEORY AND SIMULATIONS

Abstract

The overall purpose of this study is to investigate expiratory events such as coughs and sneezes in the ejection scale framework, i.e. within a short time span immediately after the expiration process. We conducted large eddy simulations (LES) and compared the results with a recent theoretical model put forth by Balachandar et al. [2]. The theoretical model [2] has been formulated to estimate the evolution of expiratory events such as coughs and sneezes. Some of the key features of the model include estimates for the time evolution of the puff centroid, its size, as well as the number and size of droplets suspended within. The theoretical model includes closure parameters that have been obtained from LES [6, 7]. The simulations cover a wide range of parameters, such as the ejection volume of the puff, its momentum, the ejection angle (whether horizontal, inclined, or vertical), and the ambient humidity. One of the important findings is that while certain aspects such as the front-most location and the lateral extent of the puff, show large variability from one realization to the other, global parameters, such as the centroid location, total volume, and buoyancy show are much less sensitive to turbulent fluctuations. The results also indicate that humid ambient conditions favor stronger gravitational settling of the ejected virus-laden droplets, thus decreasing the risk of infection from the dominant airborne route. Furthermore, the simulations highlight a mechanism for transporting a relatively large amount of droplets over distances upward of 2 meters in a time span on the order of one second. This mechanism, which is also observed in experiments, consists of fast moving detached vortex rings that propagate in a seemingly random direction. We further quantify the size and viral content of the detached portions. © 2022 Begell House Inc.. All rights reserved.