A numerical investigation on the effects of passenger movement on droplet dispersion in a high-speed train compartment

Cough droplets pose significant risks to human respiratory health, potentially leading to severe infections in indoor environments. In the confined and densely populated high-speed train compartment, passenger movement is unavoidable and follows a fixed path. This movement impacts the designed airflow and, consequently, influences the dispersion of cough droplets. In this study, a validated computational fluid dynamics overset mesh method was adopted to implement passenger movement along the aisle, and the impact of passenger movement on droplet dispersion inside a high-speed train compartment was investigated. The results show that the wake flow generated by moving passengers can carry cough droplets along the direction of movement. The timing and speed of passenger movement play a pivotal role in the extent of droplet dispersion. Premature and delayed interactions with the droplet cloud diminish engagement due to inadequate and excessive dispersion, respectively. When a passenger begins walking at the 10th second, droplet transfer in the direction of movement peaks, reaching up to 4.9 times that of the stationary case in the area of seat 13A, with droplet transmissions extending up to 6 m. The walking speed affects the intensity of the wake flow. A walking speed of 1.0 m/s or higher results in the noticeable transmission of droplets in the direction of the walking passenger. These findings underscore the necessity for incorporating human movement dynamic in the development of ventilation strategies and public health guidelines to mitigate airborne transmission risks in enclosed public spaces.