Large eddy simulation of cough jet dynamics, droplet transport, and inhalability over a ten minute exposure

High fidelity simulations of expiratory events such as coughing provide the opportunity to predict the fate of the droplets from the turbulent jet cloud produced from a cough. It is well established that droplets carrying infectious pathogens with diameters of 1 - 5 mu m remain suspended in the air for several hours and transported by the air currents over considerable distances (e.g., in meters). This study used a highly resolved mesh to capture the multiphase turbulent buoyant cloud with suspended droplets produced by a cough. The cough droplets' dispersion was subjected to thermal gradients and evaporation and allowed to disperse between two humans standing 2 m apart. A nasal cavity anatomy was included inside the second human to determine the inhaled droplets. Three diameter ranges characterized the droplet cloud, < 5 mu m, which made up 93% of all droplets by number; 5 to 100 mu m comprised 3%, and > 100 mu m comprising 4%. The results demonstrated the temporal evolution of the cough event, where a jet is first formed, followed by a thermally driven puff cloud with the latter primarily composed of droplets under 5 mu m diameter, moving with a vortex string structure. After the initial cough, the data were interpolated onto a more coarse mesh to allow the simulation to cover ten minutes, equivalent to 150 breathing cycles. We observe that the critical diameter size susceptible to inhalation was 0.5 mu m, although most inhaled droplets after 10 min by the second human were approximately 0.8 mu m. These observations offer insight into the risk of airborne transmission and numerical metrics for modeling and risk assessment.

Automated summary

This study used high-fidelity simulations to predict the dispersion of droplets produced by coughing, showing that droplets with small diameters mainly contribute to the risk of respiratory transmission.