Numerical Study of the Effect of Air Curtains on Smoke Blocking and Leakage Heat Flux in Tunnel Fires

Tunnel fires can result in serious casualties, and air curtains are crucial for tunnel fire prevention and control. This study adopts a theoretical analysis and Fire Dynamics Simulator (FDS) full-scale numerical simulation to investigate the longitudinal variation law of heat decay under natural ventilation and air curtain jet conditions, as well as the flow characteristics of the flow field, temperature rise, and smoke prevention efficiency changes under different air curtain jet effects. The results indicate that the air curtain can effectively isolate the diffusion of heat flow. As the jet velocity increases, the temperature difference between human height and the ceiling decreases. For the 20 MW heat release rate, the minimum jet velocity is 15 m/s, and the greater the jet velocity and width of the air curtain, the smaller the leakage heat flux and the greater the smoke prevention efficiency. The smoke prevention efficiency reduction rate gradually decreases as the jet angle increases, and dimensionless analysis is used to obtain the power-law equations of the leakage heat flux with the fire source, jet velocity of the air curtain, jet width, and jet angle. The error between the model prediction and measured leakage heat flux is within ±20%.