| Although long highway tunnel fire happen at low frequency, it has serious damage and effect on structure and people in tunnel. To meet the urgent need of fire safety system research for the long highway tunnels, this paper presents three-dimensional transient numerical simulation on development process of fume behavior when fire occurs in a highway tunnel using Computational Fluid Dynamics.Firstly, the paper introduces mathematical model of tunnel fire simulation. The finite volume method was used to discrete the governing equations and the SIMPLE algorithm was employed to solve the discretized equations. The calculation result of numerical simulation indicates that the proposed fire model is reasonable. Then, the development law of temperature field, velocity field and concentration field of fire tunnel is analysed, it advises that longitudinal ventilation velocity should be adjusted based on the heat release rate. Hydraulic jump appears obviously in fire tunnel, analyzing the temperature field distribution of vertical section , cross section and horizontal section is conducive to overall understanding of the characteristic of hydraulic jump. In this paper, a conception of hydraulic jump length is proposed. Hydraulic jump length will increase and hydraulic jump will be weakened when longitudinal ventilation velocity increases, the increase in heat release rate makes hydraulic jump length shorter. The length of back-layering and fume transmission of downstream is different when the slope of tunnel changes, how the temperature field and concentration field distributed in different slope of tunnel is also introduced in the paper. It advises that the direction of longitudinal ventilation should be upslope.The research findings in this thesis provide that using three-dimensional field model of tunnel fire can simulate development process of fume behavior of different conditions, and has important reference value for further research on tunnel fire and ventilation.
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