Experimental Study On Temperature Field And Smoke Flow Of Fire In Subway Section Tunnels By Longitudinal Ventilation

The subway is a semi-enclosed underground space,when fire occurs in subway tunnels,it will cause a large number of casualties.Many researches have been done about the smoke spread and temperature distribution of tunnel fires at home and abroad.However,there are the difference in the basic structure,ventilation mode and fire scale of different types of tunnels which resulting in different laws of temperature field and smoke flow.Longitudinal ventilation as an important ventilation method in subway tunnel,is one of the main factors affecting fire development in subway section tunnel.Therefore,the temperature field and smoke flow characteristics of subway tunnel fire are studied in detail in this paper.This paper takes a certain subway section tunnel in xi'an city as a model,and the similarity principle is adopted to establish the similarity relationship between the original model and the small-size model,then and a 1/10 small-size experimental platform is established to test the combustion and flue gas spreading process with different fire source power and ventilation speed.The experimental results show that the longitudinal ventilation can change the combustion pattern of the fire source and the flue gas flow state on the downwind side of the fire source,leading to the increase of flue gas layer thickness and flame area.When the longitudinal ventilation,velocity are 0.6 m/s,0.8 m/s,1.0 m/s,flame inclination are 35°,45°,55°respectivelyFDS numerical simulation,software was used to simulate the changes of heat radiation temperature field and smoke flow velocity of subway tunnel roof under different fire power and ventilation speed conditions,and the simulation results are compared with the experimental.The results shows that longitudinal ventilation reduces tunnel ceiling temperature and heat radiation while enhancing the flow of smoke;when the ventilation speed are 1.0 m/s,the velocity of smoke gas is 1.25 m/s?1.45 m/s,and the temperature near the fire source and in other areas decreases about 60?,30? respectively compare with the ventilation speed is 1.0 m/s,and the temperature decreases by about 80?120? compare with the condition without ventilationCombined with small-size experiment and simulation results,the attenuation model of fire smoke temperature in the ceiling of subway tunnel under longitudinal ventilation condition is established,and the relationship between ventilation speed and attenuation coefficient is obtained.Based on the existing tunnel fire experimental data,back-layering length of smoke and the power of fire source are processed dimensionless,and the prediction and correction models of smoke back-layering length and the critical speed are obtained,and the differences between them and several classical models are analyzed.The results show that the modified smoke back-layering length prediction model is higher than several classical models,and the error the experimental critical speed is less 5%than them;Combined with the experimental data of fire source power of 2?10 MW previously,a more universal critical speed model of subway tunnel fire was obtained.This paper provides a certain experimental basis and reference significance for the study of subway tunnel fire.