Numerical and experimental study on smoke diffusion characteristics of tunnel with ceiling beams

Ceiling beams at the top of tunnels are more common in actual projects. Under the influence of thermal buoyancy, the ceiling structure significantly affects the diffusion characteristics of fire smoke within the tunnel. This study performed several sets of model experiments and numerical simulations to investigate the impact of the height and spacing of ceiling beams on the diffusion of smoke in tunnel fires, which results show that the maximum temperature rise and temperature decay patterns of fire smoke follow exponential changes. The increased height of the ceiling beams and the reduced spacing correspond to higher maximum temperatures on the ceiling. Furthermore, as the height of the ceiling beams increases and the spacing decreases, the longitudinal attenuation of ceiling temperature accelerates within the tunnel. A predictive model for ceiling temperature rise and a dimensionless temperature attenuation model were developed to characterize this phenomenon. The relative error between the predicted results and experimental findings falls within ± 15%. This study broadens the application scope of fire smoke diffusion models, which can provide technical support for smoke prevention and exhaust design of tunnels with similar structures.