| The installation of smoke control system in a metro tunnel is a necessary measure to ensure safety evacuation for fire victims.The longitudinal ventilation system in a metro tunnel is usually composed of the tunnel fans located at the stations and jet fans arranged in the middle of tunnel.At present,the study of the longitudinal ventilation in a tunnel is mainly focused on the influence of longitudinal ventilation formed by tunnel fans on the smoke flow,but there are few studies on the influence of longitudinal ventilation formed by jet fans on smoke flow.Because of the unique distribution characteristics of flow field in the jet development process formed by jet fan,the distance between jet fan and the fire source will influence the distribution of smoke temperature in the tunnel.Therefore,the study on the influence of relative position of jet fan and fire source on the smoke temperature distribution is necessary.The research results of the smoke temperature distribution under the longitudinal jet ventilation have important theoretical significance and practical value for guiding the engineering design of the longitudinal ventilation system in a metro tunnel.The small-scale model tunnel with dimensions of 13m(Length)* 0.32m(Width)* 0.48 m(Height)is built according to Froude similarity criterion based on a real interval tunnel from Chongqing rail transit line six with the scale of 1:15,and the CFX software is used to carry out numerical simulation calculation with a full-scale model tunnel built by ANSYS ICEM 17.1.The influence of the distance between the fire source and jet fan,the fire power and the outlet velocity of jet fan on the smoke temperature distribution is studied by combining the small-scale experiment with the CFX numerical simulation.The small-scale experiment scheme is designed as follows: the distance between jet fan and fire source is 5m and 3m,the fire power is 2.92 kW,4.31 kW and 5.79 kW,the jet velocity includes 5 values between 4-12m/s.After analyzing the experimental data,the temperature decay factor in the upstream and downstream of fire sources is obtained.In addition,when the fire source is located in the even jet velocity distribution area,the temperature correction factor was introduced into the upstream temperature decay equation.Five different distances between jet fan and fire source were designed to carry out CFX numerical simulation under 2m/s longitudinal velocity provided by tunnel fan located at the station.The temperature decay equation in the upstream of the fire source is verified by numerical simulation,and the temperature distribution of tunnel ceiling is studied when the fire source is located in the area of uneven jet velocity distribution.The results show that when the fire source is located in the area closer to the fan,smoke mainly accumulates in the lower part of the tunnel,which is unfavorable for personnel evacuation in the downstream of fire source. |
PDF Full Text Request