Investigation of airborne transmission and thermal comfort in a train cabin: Effects of air change rate and supply mode

Developing ventilation strategies that balance protection, comfort, and well-being is crucial for efficient train operations and enhanced passenger experience. Although raising the Air Change per Hour (ACH) can mitigate bioaerosol transmission, it may induce undesirable airflow disturbances and increase energy consumption. To elucidate the roles of ACH and large-scale airflow patterns, a three-dimensional computational fluid dynamics (CFD) model based on the Eulerian-Lagrangian approach is established. The study investigates the impacts of particle size, ventilation configuration, and airflow velocity on the cabin environment. Results indicate that simply intensifying ventilation does not consistently reduce aerosol deposition on passengers due to the asymmetric arrangement of seats and vents. Excessive ventilation (24 ACH) demonstrates clear diminishing returns in performance, whereas inadequate ventilation (6 ACH) significantly elevates aerosol concentration and infection risk. Compared with merely boosting the ventilation rate, optimizing the supply layout is more effective for achieving a safe and comfortable environment. At 12 ACH, the sidewall air supply mode outperforms the top air supply mode in controlling aerosol deposition on passengers, while lowering the airflow non-uniformity index by 20.0% and the draught rate ( ) in the breathing zone by 32.1%. These findings provide guidance for improving train cabin ventilation toward coordinated management of infection control, comfort, and energy utilization.