Numerical study of cough droplet transmission in an indoor environment

The Coronavirus Disease 2019 pandemic has become an unprecedented global challenge for public health and the economy. As with other respiratory viruses, coronavirus is easily spread through breathing droplets, particularly in poorly ventilated or crowded indoor environments. Therefore, understanding how indoor environmental conditions affect virus transmission is crucial for taking appropriate precautions. In this study, the effects of different natural wind-driven ventilation conditions and ambient relative humidities (RHs) on the cough droplet transmission in an indoor environment are investigated using the large eddy simulation approach with Lagrangian droplet
tracking. The simulations show that the velocity and temperature of droplets significantly decrease in a short time after ejection. This feature for droplet velocity and temperature is more pronounced at smaller inlet wind speed (V_in) and larger V_in or lower RH, respectively. Wind-driven ventilation plays a crucial role in affecting the horizontal transmission distance of cough droplets. Under strong natural ventilation conditions (V_in=4.17 m/s), cough droplets can spread more than 4 m within 1 s, whereas they can only travel within 2 m under weak ventilation with V_in=0.05 m/s. The results confirm that the social distancing of 2m is insufficient, while revealing that proper ventilation control
can significantly remove virus-laden droplets from indoor air. We believe that there is no absolute safe social distancing because the droplet transmission and dispersion are mainly controlled by the local environmental conditions, and for safety, we recommend wearing a face mask and maintaining good indoor ventilation to reduce the release of potentially virus-laden droplets into the air.