纵向通风与狭长受限边界耦合作用下隧道火灾强羽流驱动顶棚射流的卷吸特性与扩展行为研究

Classical theory of tunnel fire ceiling jet were built just for weak plume condition (flame height is lower than ceiling). However, for the ceiling jet behavior induced by strong plume condition (flame impinge upon the ceiling), classical theory of fire dynamics is limited to the unconfined compartment ceiling without wind effect, the characteristic parameters distribution presents one dimensional axisymmetric phenomenon, it will not apply to tunnel fire. This research focuses on the investigation of tunnel fire ceiling jet entrainment characteristic and asymmetric extension behavior induced by strong plume condition under combined influence of longitudinal ventilation and long-narrow confined effect, which includes: (1) The tunnel ceiling jet entrainment characteristics will be revealed. (2) A mathematical model will be developed to predict the tunnel ceiling jet flame extension length. (3) The tunnel ceiling jet smoke back-layering length model will be established. The complex entrainment and extension behavior of ceiling jet, induced by strong plume condition under combined influence of longitudinal ventilation and long-narrow confined space, cannot be predicted by the classical models. The results of this research will able to enrich the current classical theory of ceiling jet in this aspect. This research has important scientific significance, as well as the practical value for fire resistance of structure, fire detection and alarm, evacuation and rescue and the relevant fire prevention standard formulation in tunnel fire.

现有隧道火灾顶棚射流的经典理论仅基于弱羽流驱动条件（火焰高度未及顶棚）建立；而针对强羽流驱动（火焰撞击顶棚）的顶棚射流行为，现有火灾动力学的经典理论局限于室内无风条件的非受限顶棚一维轴对称扩展，不适用于隧道火灾。本项目拟研究揭示纵向通风与狭长受限边界耦合作用下、隧道火灾强羽流驱动顶棚射流的卷吸特性与非对称扩展行为：(1)揭示纵向通风作用下隧道火灾强羽流驱动顶棚射流的卷吸特性；(2)建立纵向通风作用下隧道火灾强羽流驱动顶棚射流的火焰扩展长度模型；(3)建立纵向通风作用下隧道火灾强羽流驱动顶棚射流的烟气逆流长度模型。对于纵向通风与强羽流耦合驱动下、顶棚射流在狭长受限空间内的复杂卷吸与扩展行为，现有的经典模型不再适用，本项目有助于弥补现有的顶棚射流经典理论在这方面的不足，具有重要科学意义；同时，对于隧道火灾结构抗火、探测报警、人员疏散与应急救援及相关防火标准的制定，也具有应用参考价值。

现有隧道火灾顶棚射流的经典理论仅基于弱羽流驱动条件（火焰高度未及顶棚）建立；而针对强羽流驱动（火焰撞击顶棚）的顶棚射流行为，现有火灾动力学的经典理论局限于室内无风条件的非受限顶棚一维轴对称扩展，不适用于隧道火灾。. 因此，本项目针对纵向通风与狭长受限边界耦合作用下、隧道火灾强羽流驱动顶棚射流的卷吸特性与非对称扩展行为，采用理论分析和实验研究相结合的方法，并辅以数值模拟分析，揭示了隧道火灾强羽流驱动顶棚射流的卷吸特性，阐述了隧道火灾强羽流驱动顶棚射流的火焰扩展长度和烟气逆流长度的变化规律。同时，基于研究数据，建立了隧道火灾强羽流驱动顶棚射流的火焰扩展长度模型和烟气逆流长度模型。. 研究发现：1）连续火焰区域的羽流流速最高，而在间歇火焰区的羽流流速会降低，随后在浮力羽流区的羽流流速开始回升，并且离火源的位置越远，羽流流速越高。2）无风时，顶棚下火焰扩展长度随着火源功率的增大和顶棚与火源之间间距的减小而逐渐增大；当风速逐渐增大时，火源上游的火焰扩展长度迅速减小，而火源下游的火焰扩展长度变化很小。3）火源功率和顶棚与火源之间间距对火源上方高温区域范围的影响较大。4）当火源功率较小时，烟气逆流长度随着火源功率的增大而增大；当火源功率较大时，烟气逆流长度基本只与纵向通风速度有关。5）建立的预测模型与研究数据具有较高的吻合度。. 本项目的研究丰富了隧道火灾强羽流条件下的火灾特征参数数据，补充了现有隧道火灾顶棚射流基础理论。同时，对于隧道结构抗火设计及相关防火标准的制定提供了理论依据和技术支撑。