عنوان مقاله [English]
Simulation of fluid flow within tunnel is an appropriate and relatively cheap way to investigate the spreading of the pollutants and the efficiency of tunnel ventilation system. In this research, the tunnel of Tehran-Tabriz line is studied from this aspect. This tunnel is 8 km long and 32 m width, and the locmomotive ER24PC passes from it. Ventilation of this tunnel is of great importance because of considerable length of the tunnel with 4 parallel lines in urban area and because of passage of the old diesel locomotives through it. Fluent software is used for numerical analysis and modeling of a length of 200 m of the tunnel. The species of each gases in combustion product mixture of ER24PC locomotive are obtained using emission standard EU III A. The molar ratio of pollutants in the exhaust of the locomotive is calculated using equilibrium equation of combustion, and then, is entered to the non-premixed combustion toolbox of the software to specify the volume fraction. In the critical case, two trains with a speed of 50 km/hr moving toward each other in the parallel lines are considered. The simulation is carried out by using dynamic mesh and UDF motion code. The simulation is validated by experimental work reported in references. The performance of ventilation system, temperature distribution along the tunnel and the effect of the motion of the train on spreading pollutants are investigated.
In this study, simulation of moving ER24PC (Siemens) locomotive in three dimensional (3D ) mode is made by using dynamic mesh in the Fluent software. The modeling of moving locomotives is a new idea in the field of tunnel ventilation. Thus, the distribution of outlet pollutants is investigated in both length and cross sections of the tunnel due to the motion of the train, and also, the effect of the motion of the train on spreading CO and Nox is investigated.
Ventilation of tunnels is important in two applications of traffic and fire mode. In recent years, some disasters due to tunnel firing, for example in Baku or Daegu metro, have occurred that show the importance of fire and smoke ventilation in tunnels. The initiation of fire in tunnel produces a huge amount of smoke, which moves to the ceiling due to the buoyancy effect, and spread out in both sides. The task of tunnel ventilation system in this critical mode is to push the smoke into one side, and make a safe passage for passenger escape or rescue team.
Methodology and Approaches
In this study, locomotive emissions are simulated as a moving point and as a result, pollutants spread in 3D space. The combustion products of the locomotive are obtained by considering the MTU engine exhaust emissions and using Emission standard EU III A. The volume fraction of each pollutant is calculated from the equilibrium equation of combustion and is entered into the non-premixed combustion toolbox of the Fluent software. The moving train is modeled using dynamic mesh and employing UDF motion code. The velocity of the trian is considered to be 50 km/hr and two crossings against train are considered as a critical mode.
Results and Conclusions
In the case of no forced ventilation in tunnels, it can be seen that the motion of trains induces air flow passing above the train that causes the spread of smoke behind of the train. The maximum temperature and concentrations of pollutants happen above the chimney of the locomotive, and decrease toward the start point of motion. The temperature and concentration values of pollutants in the tunnel cross-section are independent when the incoming trains are at the near wall line or center line. The results also show that the concentrations of toxic gases from the ER24PC locomotive do not reach to the critical values as long as the locomotive in the tunnel is moved.