Numerical analysis of the mirco-particles distribution inside an underground subway system due to train piston effect

The train movement in a model of the subway tunnels and stations with a side-platform was simulated using a 3D computational model. The impact of airflow mainly due to piston effect on distribution of particles generated due to the train braking was investigated. The unsteady RANS and energy equations were solved using the dynamic mesh technique with an Eulerian approach. The particle trajectories were evaluated by the Lagrangian approach. The particle concentration in different points of the station emitted due to the train braking is obtained and discussed. The results showed that when the train enters the station while braking, a fraction of particles is transported and spread into the platform areas. Some of the generated particles, however, were accumulated in the rear of the train. When the train stops, these particles entered into the station due to continuation of the piston effect. The simulations showed that particles would spread in the platform and penetrate into the staircases and ticket hall, and even disperse into the outside ambient. The results also demonstrated that some of the particles released from the braking system of the train could penetrate into the train through the ventilation system of the passenger cars. •The impact of piston effect on distribution of braking particles in subway system is studied.•Most of the particles were accumulated in the train rear and entered the station due to the piston effect.•Particles spread in the platform, ticket hall, and even reach to the outside ambient.•Particles could penetrate into the train through the ventilation system of passenger cars.•The number of entering particles is reduced along the train from the rear to the head.