低压条件下顶棚射流卷吸行为与特征参数演化研究

The physical mechanism of fire plume entrainment and the driving force of fire smoke spread at reduced pressure should be definitely different from those at normal pressure condition. Thus, the entrainment behavior and characteristic parameters of the ceiling jet induced by fire plume impinging against the ceiling should be altered, where the current classical ceiling jet theory is no longer suitable for the ceiling jet under reduced pressure conditions. Theoretical analysis, experimental research and numerical simulation will be conducted to investigate the ceiling jet entrainment behavior and characteristic parameter evolution at reduced pressure conditions:.(1) The mechanism of low pressure effect on the ceiling jet will be discovered. The theoretical model of ceiling jet entrainment amount will be deduced, and the entrainment coefficients under different low pressure conditions will be acquired..(2) Mathematical models of ceiling jet characteristic parameters (including the velocity profile, maximum temperature rise, temperature profile and flame extension length) will be proposed for different low pressure conditions..This project can improve the ceiling jet theory in the limitation of low pressure conditions. The findings of this project will also be practical helpful for the setup of fire detection, the and automatic sprinkling system and the design of building structure fire resistance under reduced pressure conditions.

在低压条件下，火羽流卷吸的物理机制和烟气蔓延的驱动力将发生重要变化，由此将导致火羽流撞击顶棚后形成的顶棚射流具有不同于常压条件下的卷吸行为及特征，现有顶棚射流经典理论不再适用。本项目拟通过理论分析、实验研究和数值模拟分析，揭示低压条件下顶棚射流卷吸行为及其特征参数演化规律：.（1）揭示低压条件对顶棚射流卷吸行为的影响机制，建立低压条件下顶棚射流卷吸量及其卷吸系数的理论模型。.（2）建立低压条件下顶棚射流动力学特征参数（速度分布、最高温升、温度分布、火焰扩展长度）演化的预测模型。.本项目有助于在理论上弥补顶棚射流经典理论在低压条件下的不足；同时对于指导低压条件下火灾探测、自动灭火系统及建筑结构抗火设计，具有参考价值。

在低压条件下，火羽流卷吸的物理机制和烟气蔓延的驱动力将发生重要变化，由此将导致火羽流撞击顶棚后形成的顶棚射流具有不同于常压条件下的卷吸行为及特征。因此，本项目对低压条件下顶棚射流卷吸特性、温度分布表征模型和火焰扩展长度等内容开展了理论和实验研究，并辅以数值模拟分析。首先，得到了不同低压条件下顶棚射流卷吸系数，明确了低压条件对顶棚射流卷吸行为的影响机制，为后续顶棚射流温度分布和火焰扩展长度的研究奠定理论基础。然后，进一步分析了不同低压和抬升高度下火羽流中心线温升和顶棚最高温升变化规律，根据实验数据确立理论关系中的耦合参数，建立适用于低压条件下弱浮力羽流和强浮力羽流驱动的火羽流中心线温升和顶棚最高温升预测模型。基于低压条件下卷吸特性和经典火焰高度模型，建立了适用于不同火源抬升高度和低压条件火焰高度和顶棚射流扩展长度预测模型。最后，研究了低压和侧壁限制耦合作用条件对火羽流温度及火焰形态的影响机制，建立其预测模型。本项目有助于在理论上弥补顶棚射流经典理论在低压条件下的不足；同时对于指导低压条件下火灾探测、自动灭火系统及建筑结构抗火设计，具有参考价值。