Numerical Evaluation of Ventilation Efficiency in Underground Metro Rail Transport Systems

Ventilation system is the most important component of the subway systems when events involving heavy smoke occur. Consequently, the objective of this study is to analyse the ventilation efficiency in one of the most dangerous scenario: train on fire and stopped in the tunnel, the incident demanding immediate passenger evacuation. The ventilation strategy taken into account is based on mid-tunnel fan plant located in separate construction in conjunction with stations mechanical ventilation. The analysis is performed using Computational Fluid Dynamics (CFD) modeling. The approach is based on the introduction of source terms in conservation equations for energy and dioxide carbon (CO2), in order to deal with the heat and CO2 due to fire. The equation expressing the conservation of CO2 is added to the basic equations governing a turbulent non-isothermal air flow in the CFD model. This method allowed achieving values of velocity, temperature and CO2 concentrations all over the computational domain. The results show that the ventilation system taken into account provides the secure evacuation of passengers all over the simulation time. The evacuation process toward the nearest station is not at all disturbed by too high air velocities, high temperatures or dangerous CO2 concentrations.