地下分岔道路分流点位置火灾工况的顶棚温度分布实验研究OA

[Objective]In this study,a theoretical analysis and scale-down experiments were conducted to investigate fire scenarios at the merging and diverging sections of urban underground road tunnels.[Methods]Based on the Froude scaling law,a 1∶20 small-scale curved ramp tunnel fire experimental platform was constructed to perform the fire experiments.The environmental characteristics affected by tunnel fires were investigated under natural ventilation conditions,and the centerline temperature distribution of fire smoke in the tunnel was quantified using a prediction model.For the natural ventilation scenarios,five heat release rates(1.71,3.43,5.13,6.85,and 7.70 kW,corresponding to full-scale values of 2.31,3.86,4.92,5.40,and 13.77 MW,respectively)and five different transverse fire source positions were used to quantify the influence of the transverse fire source position on the maximum smoke temperature rise beneath the tunnel ceiling.When the fire source position remained constant,the maximum temperature rise below the tunnel ceiling increased with increasing fire source heat release rate.Under the same heat release rate,the closer the fire source was to the tunnel sidewall,the higher the maximum temperature rise beneath the tunnel ceiling.This occurred because the tunnel sidewall restricted the entrainment of cold air by the fire plume,thereby decreasing the temperature of the confined fire plume.Meanwhile,continuous combustion near the sidewall increases the sidewall surface temperature,thereby enhancing thermal feedback to the fire source and increasing the maximum temperature beneath the tunnel ceiling.A comparative analysis of the maximum smoke temperature at different transverse positions in the merging and diverging sections of urban underground road tunnels showed that the closer the fire source was to the tunnel sidewall,the higher the maximum ceiling temperature.[Results]When the fire source was at different transverse positions at the merging and diverging sections of urban underground road tunnels,the downstream smoke temperature decay rate for conditions where the distance of the transverse fire position to the tunnel sidewall increased from 0.05 m(wall fire)to 0.30 m was lower than that for conditions where the distance of the transverse fire position to the tunnel sidewall increased from 0.35 m to 0.55 m.When the fire source was close to the sidewall(D≤0.35m),the longitudinal temperature was primarily influenced by the sidewall effect.When the fire position was far from the sidewall(D>0.35 m),the longitudinal temperature was primarily affected by the branch tunnel.To quantitatively analyze the impact of the distance between the fire source and the tunnel sidewall on the maximum smoke temperature rise beneath the tunnel ceiling,it was assumed that the plume velocity and temperature followed a Gaussian distribution,and the plume velocity and temperature at a given radial position were independent of height,thus modifying the influence factor αL of the temperature prediction model.[Conclusions]This comprehensive study deepens the understanding of fire dynamics in complex tunnel junction environments and offers practical insights for optimizing safety designs and operational strategies in urban underground infrastructure,thereby enhancing the overall resilience of tunnel systems against fire emergencies.