With train speed increasing, the heat generation from its key equipment is growing as well and the cooling and ventilation of the equipment cabin become more and more important. In this paper, computational fluid dynamics (CFD) method is adopted to simulate the airflow and the temperature field in indoor and outdoor space of the equipment cabin when the train moves at 250 km/h in open space. The simulation results indicate that the surface temperature of the main heat generation equipment is not beyond the limit. When the train moves forward and backward, the maximum average surface temperature of the heat generation equipment is 56.5 °C and 71.7 °C, respectively, and the airflow rates of the fans in the equipment cabin are decreased by 9.1% and 5.2%, if compared to the rated value, respectively. Both forward and backward running conditions should be considered when designing the layout of the equipment and grilles. It is suggested that, the major heat generation equipment should be located in the middle of the cabin; the flow rate decrement of the cooling fan when the train moves at 250 km/h should be taken into account.

This paper adopts an Eulerian-Lagrangian approach to investigate the lock-up phenomenon (or trap phenomenon) of human exhaled droplets in a typical office room under displacement ventilation (DV). A particle-source-in-cell (PSI-C) scheme is used to correlate the concentration with the Lagrangian particle trajectories in computational cells. Respiratory droplets with sizes of 0.8 μm, 5 μm and 16 μm are released from a numerical thermal manikin (NTM). The influence factors including indoor temperature gradient, heat source configuration and exhalation modes are studied. It is found that large temperature gradient would result in trap phenomenon of small exhaled droplets (smaller than 5 μm). The intensive heat source near the NTM could help to transport the small droplets to the upper zone and decrease the concentration level in the trapped zone. Both nose-exhaled and mouth-exhaled small droplets would be trapped at the breathing height when temperature gradient is sufficiently high. However, the trap height of the droplets from mouth is a little bit higher. Because of large gravitational force, it is difficult for the thermal plume to carry 16 µm respiratory droplets to the upper zone.