Fire Numerical Simulation Of Tunnel Longitudinal Ventilation

With urbanization continuing to accelerate worldwide, problem of traffic congestion in cities is becoming more and more serious. Construction of city tunnels (including subway tunnel, underground highway tunnel, underwater tunnel, etc) has greatly improved city traffic condition. The rapid development of city tunnels effectively relieved traffic congestion, but also increases the risk of fire at the same time. Compared with ordinary highway tunnel, city tunnel is lower in clear height, and jet flame zone is easily formed below the tunnel ceiling once traffic caught fire, which under certain conditions will ignite nearby traffic and leads to the spread of fire in jumps. City tunnel fire prevention has been a current focus among researchers as it is more dangerous and destructive compared with ordinary highway tunnel fire.The paper summarizes the cause, feature and harm of tunnel fire and the present research status at home and abroad are discussed. On this basis, this study puts forward the research contents. Firstly, flue gas flow, critical wind velocity and law of ceiling temperature field of tunnel fire are theoretically analyzed and a mathematic model is developed. Then analysis software of FDS is used to simulate the critical wind velocity and temperature field of tunnel fire. The results show that:1、Critical wind velocity with fire size at3MW(cars caught fire) and20MW(mid-size buses caught fire) are analyzed respectively;2、Ceiling temperature field under conditions of two fire sizes and temperature changes under different fire scale, ventilation speed in different places of ceiling are studied;3、Temperature field and flew gas field respectively under ignition face of lm, fire size of3MW and under ignition face of3m, fire size of20MW are constructively posed; and differences between ignition mode of longitudinal profiles and ordinary ignition mode are analyzed;4、Virtues or defect degree of different ventilation schemes in fire compartment of one-way double tunnel under condition of longitudinal ventilating using jet-flow ventilator are investigated and the best ventilation design is proposed;5、According to the numerical simulation of fire and smoke spread of one-way double tunnel, the paper offers a simple guidance to designing the best scheme for evacuation; 6、Finally, tunnel fire prevention under condition of longitudinal ventilating are discussed from aspects of high temperature and poison gas, and preventive measures are recommended.