Study On Back-layering Length In Curved Tunnel Fire Under Longitudinal Ventilation

Smoke control is one of the most important measures to ensure the safe evacuation in a subway tunnel when a fire accident happens.At present,the research on smoke flow characteristics of tunnel fire is mainly aimed at smoke control and its characteristics in straight interval tunnel.However,the smoke flow characteristics of the curved interval tunnel and straight interval tunnel are quite different.Due to various reasons such as distribution of rail transit stations and terrain restriction,it is inevitable to involve a curved tunnel in practical engineering.Therefore,it is of great theoretical significance and engineering application value to systematically study the influence of curvature on the smoke flow characteristics of the subway tunnel fire.Summarizing and analyzing the previous research is the foundation of this study.Based on the group project,this paper investigates and analyzes the Chengdu Metro Line 9 about the curve radius,tunnel length,line form and laying mode and so on.The investigation shows that the total length in this project is about 23 km,the length of the curve section is about 9.74 km,which accounts for 42% of the total line length.Through the small-scale experiment table built by the project group,the small-scale experiment is carried out.The calculated values of the ceiling temperature of the FDS numerical simulation and small-scale test are compared to verify the setting of grid and the boundary conditions in the numerical simulation.Then,several numerical simulations are developed to discuss the smoke flow characteristics in curved tunnel.The radius of the tunnel is an important parameter that characterizing the curve interval.The relationship between the radius of the tunnel curve and the length of the back-layering length and the critical velocity is studied in this paper.Through dimensionless analysis,the prediction model applicable for curved tunnel smoke back-layering length and critical longitudinal velocity is put forward.It is found that the larger the radius of the tunnel is,the longer the smoke back-layering length is,the greater the critical wind speed is.