Numerical Simulation Of Smoke Exhaust Effect In Urban Traffic Link Tunnel With Longitudinal Ventilation

Urban Traffic Link Tunnel (UTLT) is a novel type underground transportationsystem. It consists of main tunnel with loop shape and several linked tunnels, andalways locates in the important and prosperous district. Compared with common roadtunnel, UTLT has high traffic, circular main tunnel, multiple points of entry and exit,large buried depth, narrow section. Thus, the safety of human lives and propertieswould be seriously endangered once the fire happens in such kinds of buildings. Weshould find out the smoke spread features and select the appropriate longitudinalventilation speed to determining the best solution of smoke control, these woulddischarge the smoke timely and effectively to ensure the safety of firefighters andpeople in the tunnel. These things about all have important research value.Numerical simulation is used to simulating smoke distribution and smoke speedlaw about UTLT in this study. The first thing to do is to verify the software FDS withsmall size experiments, comparing and analyzing simulating parameters such astemperature, velocity, heat release rate, visibility and so on to ensure the feasibilityand authenticity of the numerical simulation method.Based on the scale of fires and structural characteristics of UTLT, numericalmodels are established with FDS, which reveals the limitation of the formulaproposed by Wu&Baker. According to the simulation results of sixteen groups ofdifferent UTLT fire conditions, a fitting correlation for critical ventilation velocitywith heat release rate Q, tunnel hydraulic diameter H and tunnel aspect ratio n ispresented, which is validated by eight new fire conditions.Then, the critical ventilation velocities and smoke extraction volume of differentfire conditions are calculated by the fitting correction previously proposed. Bychanging the vertical ventilation velocity in UTLT and the smoke extraction volumeof the exhaust vents, the optimal smoke control scheme could be determined. Usingthis scheme, the spread length and remaining time of smoke in tunnel would getoptimal control.Lastly, on the basis of the smoke exhaust vents of an UTLT in Beijing, numericalsimulations of smoke distribution in three tunnels with different exhaust vents areperformed by FDS. Through the comparison and analysis of parameters such assmoke temperature, ventilation velocity, visibility and so on, the optimal openlocations and sizes of exhaust vents could be determined. This is very important tofurther optimize and control smoke distribution in the case of fire and effectivelyremove the smoke from tunnel in time to make sure the safety of human lives andproperties.