Abstract: In order to study the smoke flow and control effect of the new smoke exhaust method of the supplementary exhaust ducts combined with the side wall exhaust vent on immersed tunnel fire, taking Shenzhen-Zhongshan tunnel as an example, the method of combining theoretical analysis with computational fluid dynamics was used to study the flow characteristics of smoke by analyzing the critical velocity, the smoke back-layering length and the low-temperature region of smoke bifurcation. A modified model of critical velocity and smoke back-layering length of immersed tunnel fire was proposed, and a prediction model of low-temperature zone length of smoke bifurcation flow was proposed. The results show that when the dimensionless heat release rate is less than 0.139, the critical velocity is proportional to 1/3 of the dimensionless heat release rate of the fire source. When the longitudinal velocity increases from 1.5 m/s to 4.0 m/s, the peak temperatures of 10, 20, 30, 50 MW fires are reduced by 35%, 48%, 46%, 43%, respectively. Bifurcation occurs under the action of strong longitudinal velocity. The prediction model of the length of the low-temperature region of the bifurcated flow is obtained by analyzing the temperature of the tunnel center line and the side wall, and the error of the prediction result is within 10%.

Key words: immersed tunnel fire, numerical simulation, critical velocity, smoke back-layering length, smoke bifurcation