Study On Fire Smoke Flow Characteristics Of Tunnel With Extraction System

Highway tunnel is the main component of highway traffic engineering.With the rapid development of the transportation industry,more and more highway tunnels are built at home and abroad.The tunnel transportation has brought convenience to people,but also with many new problems appearing,especially the tunnel fire,although it is a small probability event,if it occurs,it will cause great economic loss and bad social impact.On the one hand,the fire will burn the facilities inside the tunnel,and high temperature will destroy the lining structure and the stability of the tunnel;at the same time,a large amount of toxic smoke generated,will cause the tunnel choking casualties.Therefore,people pay more attention to the prevention and control of tunnel fire.In this paper,the study on the characteristics and control of smoke flow in tunnel fire is of theoretical significance and practical value.This paper is based on the summarize of related research results of the domestic and foreign existing tunnel fire,by the method of theoretical analysis and numerical simulations,taking tunnel with extraction system as research object,discussing fire smoke flow characteristics of different extraction rate and different longitudinal ventilation velocity.The main research contents and achievements are as follows:(1)The research achievements of tunnel fire at home and abroad are summarized,including the research methods and means of tunnel fire.On the basis of the analysis,the paper studies the smoke flow characteristics and the necessity of the control measures in the tunnel with semi-transverse exhaust system.(2)With the domestic common highway tunnel as the research object,establish the corresponding numerical size calculation model,taking the temperature as the key control parameters,and compare the numerical simulation results with the theory of Kurioka's prediction model to obtain the reliability of numerical simulation research.(3)The temperature variation of tunnel vault on the condition of different exhaust velocity and longitudinal ventilation velocity was studied.The simulation results show that the maximum temperature decreases with the increase of longitudinal ventilation velocity and increases with the increase of exhaust gas velocity.With the same exhaust velocity and longitudinal ventilation velocity,the longitudinal gradient of the tunnel has some influence on the maximum temperature.When the slope is negative,the maximum temperature of the vault is higher than that of the corresponding horizontal tunnel.The greater the angle of slope,the more obvious the difference,and the difference will decrease gradually when the longitudinal ventilation velocity is larger.The extraction system makes the high temperature smoke generated by the fire more concentrated between the fire source and the exhaust valve,which leads to the temperature rise along the part of the vault between the smoke exhaust and the fire source,and reduces the temperature along the outside of the smoke valve.(4)Using the method of dimensional analysis,the relationship between the critical velocity and the smoke exhaust rate is derived.The back-layering length of smoke with different exhaust velocity and longitudinal ventilation velocity was studied.And the longitudinal critical velocity prediction is obtained.The results show that the back-layering length of smoke is affected by both the longitudinal ventilation velocity and the smoke exhaust rate.With the increase of the longitudinal velocity,the back-layering length of smoke decreases.Critical velocity decrease with exponential relationship with the increase of exhaust velocity.Compared with the conventional longitudinal ventilation,the smoke is extracted from the exhaust valve,which significantly reduces the amount of smoke in the tunnel,which is favorable to maintain the stratification of the fire smoke.