A numerical study of the effects of exposure conditions and human movement on cough droplets transmission and deposition

The present numerical study aimed to clarify the effects of exposure conditions and human movement on cough droplets transmission and deposition. Two human manikins stood face-to-face were constructed within a computational domain, and the dynamic mesh method was used to realize the human movement. A validated computational fluid–particle dynamic model was adopted to simulate the transport, evaporation, and deposition of droplets emitted by human coughs under varied upstream velocities and relative humidities. The findings revealed a significantly higher percentage of droplets deposited on body surfaces compared to those inhaled into the airway. Specifically, the ratio between these two fractions was approximately 5 under a calm air environment, increasing to around 20 in windy conditions due to reduced inhalation and enhanced body surface deposition at higher wind speeds. The high humidity inhibited droplet evaporation and facilitated droplet sedimentation on the ground, consequently decreasing droplets reaching the susceptible person and mitigating associated health risks. Moreover, the impact of increased distance between the two virtual humans on reducing exposure risk was found to be exponentially diminished under windy conditions. In the coughing human movement scenario, droplets deposited on the susceptible human body and inhaled into the airway increased to 1.54 and 1.66 times, respectively, under the static condition, as the induced airflow pushed the droplets closer to the susceptible human body and respiratory zone.