Effect of lateral smoke extraction on longitudinal temperature distribution in ultra-wide tunnel fires equipped with longitudinal ventilation
摘要
The maximum ceiling temperature is crucial for evaluating the thermal hazard of a tunnel fire. However, the previous study has not focused on the combined effect of longitudinal ventilation and lateral concentrated extraction with both ceiling port and sidewall vent on temperature distribution. In this study, experiments are carried out systematically for a tunnel fire under various longitudinal ventilation velocities and smoke exhaust rates, utilizing a ceiling port and a sidewall vent. The maximum ceiling temperature and temperature longitudinal decay are revealed and quantified under the combined influence of longitudinal ventilation and lateral concentrated extraction. Results show that the lateral concentrated extraction accelerates smoke movement and reduces smoke heat accumulation. The maximum ceiling temperature varies inversely with longitudinal ventilation velocity with slope of 0.39 under u´ larger than 0.19 but slightly influenced by smoke exhaust rate. The temperature longitudinal decay is accelerated by one power of longitudinal ventilation velocity that the great smoke exhaust rate ulteriorly promotes the airflow velocity. The maximum ceiling temperature was normalized by using a piecewise function, with longitudinal ventilation velocity taken into consideration. A prediction model for temperature longitudinal decay is established by incorporating the Q* and u* as key influencing factors. The findings of this study provide valuable insights for the design of smoke exhaust systems and the evaluation of fire safety in tunnels.