Study on the characteristics of fire smoke spreading in contact nodes of urban cable tunnels

To reveal the influence of urban high-voltage cable tunnel networked structures on fire spread characteristics and to provide a basis for the fire prevention and control and structural design of cable tunnels. In this paper, a full-scale field test was carried out in an urban underground cable tunnel, and a smoke spread model was constructed by using numerical simulation of fire dynamics with different structural characteristics of the tunnel coupled with the ventilation system. The fire dynamics numerical simulation is used to construct a smoke spread model coupling different tunnel structural characteristics and ventilation systems. This study numerically analyzes smoke dynamics in urban cable tunnel node fires, examining the effects of tunnel structure, cable layout, ventilation, and fire source location on temperature, CO distribution, and smoke exhaust efficiency. The results show that T-shaped nodes trap heat and increase CO concentration by 14% in the fifth layer, while cross-shaped nodes promote diffusion, lowering ceiling temperatures by 5% but reducing exhaust efficiency. Horizontal cable layouts enhance oxygen permeability by 32%, raising fire temperatures to 820 °C, whereas stacked layouts increase fourth-layer CO by 58%. A 1.2 m/s lateral wind intensifies combustion, unexpectedly raising ceiling temperatures. Mechanical exhaust strategies show that low thresholds cause instability, while high thresholds expand smoke spread risks. Fire-source location affects CO behavior, with turbulence at nodes enhancing stability. This study proposes flow-guiding optimization and real-time control strategies, offering theoretical support for tunnel fire protection. Future research should integrate experiments for refining critical parameters.