Risk evaluation of respiratory droplet dispersion in high-speed train compartments with different air circulation systems

Ongoing respiratory epidemics are raising health concerns in public transportation environments, especially in densely populated train compartments. While air circulation systems inside these compartments play a crucial role in controlling the risk of droplets carrying pathogens, the mechanisms and strategies have rarely been investigated. This study employs computational fluid dynamics (CFD) to investigate the impacts on droplet dispersion and exposure risk within passenger compartments under two prevalent air circulation modes: centralized return-centralized exhaust (CR-CE) and distributed return-centralized exhaust (DR-CE), as well as a newly proposed mode, distributed return-distributed exhaust (DR-DE). Additionally, other key influential factors, including the release source location and the respiratory jet speed, are also considered. The results indicate that the CR-CE mode exacerbates the longitudinal airflow in the passenger compartment, thereby increasing the distance of droplet transmission. In contrast, the DR-CE mode moderately restricts the range of droplet spread to a certain extent. When the release source is in the middle of the compartment, the average distance of droplet transmission can be reduced by about 30%. The proposed DR-DE mode further confines the behavior of droplet dispersion, significantly lowering the overall exposure risk for passengers. Furthermore, the results show that sneezing, compared to speaking, results in a decrease in the exposure risk peak among passengers, from approximately 95% to around 70%. The passengers in the four rows directly in front of the release source face a relatively high potential risk. These findings provide valuable insights for improving air quality and passenger safety in public transportation vehicles.