Numerical dispersion modeling of droplets expired by humans while speaking

Abstract

As known from recent COVID-19 pandemics, droplets emitted by humans during various respiratory activities can contain pathogens and be responsible for infectious disease transmission. The study of droplet dispersion is fundamental to estimate and possibly control the associated risk. Numerical simulations are useful as they make it possible to afford the complexity of this phenomenon. However, they require precise droplet and air properties as input data in order to provide reliable results. A lack of knowledge still exists due to the difficulties in measuring droplet sizes over a wide range and in capturing sizes and velocities simultaneously. In this work, numerical simulations were conducted using experimental data collected by the authors, taking advantage of innovative information about particle velocity relative to their size. Two measurement campaigns involving 20 volunteers were carried out. The size and the three velocity components of the ejected droplets were simultaneously measured for droplets down to \(\varvec{2\ \mu m}\) using an extended version of the Interferometric Laser Imaging Droplet Sizing technique. The effect of droplet initial velocity on droplet dispersion is assessed, along with the effect of other parameters, namely, ambient temperature and air ejection velocity. Both inert and evaporating droplets are considered in the simulations.