Theoretical Study And Numerical Simulation On Thermal Characteristics Of Smoke Near Fire Source In Tunnel

In recent years, the central smoke extraction system is often brought into tunnel design because of the advantages of both longitudinal ventilation and central smoke extraction. According to physical meaning, the development of fire plume can be analyzed as the propagation of smoke affected by the upstream vertical airflow and inclined airflow induced by smoke extraction. This thesis researches on the parameters of smoke near fire source, to provide theoretical evidence and references for determination of design of tunnel fire safety.Based on analyses of coupling effect of ventilation and smoke extraction, the concept of equivalent velocity was put forward. The theoretical model of the fire plume has been developed to analyze the thermal characteristics of smoke near fire source including temperature, density, velocity, radius, trajectory and offset distance of plume. Combined with the design of a long and complicated road tunnel, this thesis evaluates the thermal characteristics of smoke, taking maximum temperature rise and offset distance of plume for example. The predictions of maximum temperature rise and offset distance are in good agreement with the previous experiments results. Lastly, the dimensionless formulae of maximum temperature rise and the offset distance for application use are given out.Based on the design of a highway tunnel with central smoke extraction systems, nature gas fire has been simulated to evaluate the trajectory and structure partition of the fire plume and the maximum temperature rise of smoke underneath tunnel ceiling.3kinds of heat release rate and 5 kinds of equivalent velocity are chosen in the study. According to the results, the structure partition of simulation flame is similar with that of free flame. And the turning point of free flame is independent of heat release rate, however, the turning point of simulation flame decreases with the augment of heat release rate. And the predictions of maximum temperature rise are in good agreement with the previous experiments results. Lastly, the dimensionless formulae of temperature rise of fire plume axis and smoke underneath tunnel ceiling for application use are given out.In the finality, the problems requiring further studies are discussed.