[Objective] With the continuous development of social and economic levels and the increasing demand for a higher quality of life, the scale and quantity of transportation tunnel construction in China continue to expand. The risk and harm of tunnel fires are increasing. Previous research has focused on single or bifurcated tunnels, lacking experimental research on fires for long-distance tunnels with double-hole tunnels. [Methods] This study focuses on a typical fire scenario of a double-hole long-distance highway tunnel, conducting full-scale experiments to evaluate the diffusion characteristics and temperature distribution of smoke under natural ventilation conditions and obtains basic data on double-hole tunnel fires. From the full-scale results, a computational fluid dynamics model was built, and further numerical simulation analysis was conducted to discuss the ventilation linkage mode of double-hole tunnels under fire conditions. [Results] Smoke diffusion under different fire conditions was characterized by analyzing key parameters such as airflow velocity, smoke temperature distribution, and smoke diffusion time. The smoke control effects under different mechanical ventilation modes were compared using computational fluid dynamics tools. The results showed that: (1) Under natural ventilation conditions, when a smaller fire source power (eight oil pans) was used, the highest temperature point upstream of the fire source appeared at a height of 3 m instead of at the ceiling, and the temperature in the area between 3 and 4 m was higher. As the power of the fire source increased to 12 oil pans, the increase in thermal buoyancy increased the temperature to the highest point, approaching 3 m. (2) Mechanical ventilation reduced the doping effect of natural wind, stabilizing the distribution of the smoke layer upstream of the fire source, and the temperature upstream of the fire source was vertically distributed with the height gradient. Because of the opposite direction between mechanical and natural ventilation, the reduction in fresh air doping weakened the cooling effect of ventilation, resulting in a higher temperature under mechanical ventilation than under natural ventilation and a maximum temperature increase of 5-10℃. (3) For the flame inclination angle, as the combustion intensified, the thermal buoyancy gradually increased, and a larger plume buoyancy led to a smaller flame inclination angle. For flame length, as the heat release rate increased, the buoyancy of the plume increased, resulting in increased flame volume and length. (4) Based on the numerical simulation, the smoke control effects of single tunnel ventilation and left and right line linkage ventilation modes were compared. Under the set fire source power and position, the mode of smoke exhaust at end A and air supply at end B of the left tunnel while using the right tunnel for natural ventilation achieved the greatest benefits. [Conclusions] Smoke diffusion, temperature distribution, and fire source morphology in tunnel fires are discussed, and the ventilation mode for smoke control in tunnel fires is presented. The optimal ventilation mode under the set operating conditions is obtained from numerical simulation. The experimental results can provide data support and a technical reference for the smoke control design of tunnel projects with similar structures.
Key words
highway tunnel /
full-scale fire experiments /
numerical simulation /
smoke diffusion /
ventilation control
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