CFD SIMULATION OF OBSTRUCTED VENTILATION PORTS IN A SUBWAY TUNNEL SECTION

摘要

A CFD simulation of the air velocity in a subway tunnel section of 1400 m in length is presented. In this case of study; the simulation compares the air velocity changes when two of six natural ventilation ports are totally obstructed. They are required for hot air exhaust, smoke release and fresh air intake. The mechanical ventilation system is located inside the tunnel at 650 m from the end of a passenger platform and 750 m from the other, it is a non-symmetrical scenario. The simulation was carried in ANSYS (R) Fluent compared with NFPA calculation and considering geometries and dimensions of an actual subway section of the Mexico City. Four different numerical models were created to analyse eight different cases. The results indicate that the obstruction of the ports create a non-homogeneous distribution of the flow velocity inside the passenger platform with an approximate difference of 1.5 m/s. This value is very important in cases when the backlayering effect has to be avoided as in the case of smoke transportation, exhaust of smoke and the transport of dust or some other contaminant. The emergency procedures and the design of escape routes can be improved by considering the physical changes occurring when the ventilation ports are obstructed. Since the atmospheric pressure influence the direction and velocity of the flow coming from the non-obstructed vents.