UFII COVID-19 SEED Awardees Virtual Seminar Series

Host-to-Host Airborne Contagion As a Multiphase Flow Problem For Science-Based Social Distance Guidelines – An Update by Dr. S. “Bala” Balachandar

Distinguished Professor in the Department of Mechanical & Aerospace Engineering

Friday, November 13, 2020

The COVID-19 pandemic has brought sudden and broad social awareness about the fundamental role of airborne droplets and aerosols as virus carriers. Droplets are formed and emitted at high speed during a sneeze, and at lower speed while coughing, talking or breathing. But no two coughs or sneezes are alike – many aspects of these expiratory events vary from one individual to another. For example, a violent sneeze of a large person could generate a large puff containing a sizable number of potentially virus-laden droplets that extend much farther into the surrounding than that of a child. It is to be expected that the coughs and sneezes of even the same individual could vary from one to the next. It is perhaps less evident that two nearly identical coughs or sneezes may show substantial differences as a result of their turbulent nature. Infinitesimal differences in the initial exhalation process or in the ambient conditions can be dramatically amplified and send a cough or sneeze careening in different paths – this chaotic behavior is the so-called {\it {butterfly effect}}. Such chaotic evolution must be properly accounted in any deterministic social distancing guidelines, since such guidelines must not only safeguard under average conditions, but also take into account occasional extreme departures from the average. Despite the chaotic behavior, there are important underlying universal properties that are common across all expiratory events and the dispersive nature of the ejected droplet clouds. This work will demonstrate the ability of a simple mathematical formulation (Balachandar et al., Int J. Multiphase Flow, 2020) to accurately predict the key quantities of interest to viral contagion. Furthermore, the simulations, supported by theoretical analysis, illustrate the importance of environmental variables such as dry versus humid condition can have on the number of airborne airborne potentially virus-laden droplet nuclei.