Abstract
We discuss the temporal evolution of a cough jet of an infected subject in the context of the spread of COVID-19. Computations were carried out using large eddy simulation, and, in particular, the effect of the co-flow (5% and 10% of maximum cough velocity) on the evolution of the jet was quantified. The Reynolds number (Re) of the cough jet, based on the mouth opening diameter (D) and the average cough velocity, is 13 002. The time-varying inlet velocity profile of the cough jet is represented as a combination of gamma-probability-distribution functions. Simulations reveal the detailed structure of cough jet with and without a co-flow for the first time, to the best of our knowledge. The cough jet temporal evolution is similar to that of a continuous free-jet and follows the same routes of instability, as documented for a free-jet. The convection velocity of the cough jet decays with time and distance, following a power-law variation. The cough jet is observed to travel a distance of approximately 1.1 m in half a second. However, in the presence of 10% co-flow, the cough jet travels faster and covers the similar distance in just 0.33 s. Therefore, in the presence of a co-flow, the probability of transmission of COVID-19 by airborne droplets and droplet nuclei increases, since they can travel a larger distance. The cough jet without the co-flow corresponds to a larger volume content compared to that with the co-flow and spreads more within the same range of distance. These simulations are significant as they help to reveal the intricate structure of the cough jet and show that the presence of a co-flow can significantly augment the risk of infection of COVID-19.
Highlights
As of July 2021, the outbreak of coronavirus-based COVID-19 disease has claimed more than 4.06 million lives while 188 million people have been infected by the disease worldwide
The present study investigates the temporal evolution of the flow structures associated with a cough jet
The iso-surface of the Q-criterion showing the temporal evolution of the vortical structures associated with the cough jet without the co-flow is plotted in Fig. 3 (Multimedia view)
Summary
As of July 2021, the outbreak of coronavirus-based COVID-19 disease has claimed more than 4.06 million lives while 188 million people have been infected by the disease worldwide. Respiratory activities, like talking, breathing, sneezing, and coughing, generate respiratory aerosol droplets, which seem to be the dominant mode of transmission of the COVID-19 disease[1,2,3] as they carry infectious pathogens. The distance traveled by these aerosol particles containing pathogens depends upon the particle size as well as the velocity with which they are expelled.[4] Zayas et al.[5] suggested that around 99% of the aerosols generated during coughing are less than 10 lm in size. Wei and Li15 through their computational study predicted the spread and trajectory of particles of various sizes and showed that the smaller size droplets could travel long distances (of around 4 m)
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