窗口溢流火燃烧试验与数值模拟研究

Numerical simulation as well as experimental study of burning flames pushing out from the building openings

选取20 cm×40 cm和60 cm×30 cm两个开口工况对窗口溢流火燃烧现象进行试验和模拟研究。试验台基于ISO 9705全尺寸热释放速率试验台搭建,包括燃烧小室、模拟外壁面、温度测量系统和气体分析系统。结果表明,燃烧状态受通风因子影响较大。峰值热释放速率随通风因子的增大而增大,而达到峰值热释放速率的时间和燃烧持续时间呈相反的变化趋势。溢流火焰的壁面贴附效应与小室开口比率(宽高比)有关,宽开口火焰壁面贴附效应比窄开口明显。采用火灾动力学模拟软件FDS(Fire Dynamics Simulator)对试验结果进行数值模拟。模拟得到的热释放速率、溢流火焰温度分布、小室温度以及溢流火焰的壁面贴附效应与试验结果吻合较好。

The present article introduces our study of the burning flames pushed out of the windows of a building both experimentally as well as numerically simulated. For our research purpose, we have setup a test rig, including a combustion compartment with a modeled ex- terior wall, a temperature-measaring system and a gas-analyzing sys- tem, based on the ISO 9705 full-scale fire test facility, plus a fire simulation study eonductgd by using Fire Dynamics Simulator （FDS）. The experimental results we have gained show that the fire behavior in the compartment has greatly been influenced by the ventilation factor （AH1/2, A is the area of the opening and H is the height nftbe opening）. For the 20 cmx 40 cm opening condition （AHI/Z = 0.050 60 m5/2）, the duration of combustion is about 255 s, with the peak heat release rate （175 kW） reached at about 195 s, whereas the 60 cmx 30 cm opening with larger ventilation factor （AH1/2 = 0.098 59 m5/2）. The combustion duration and the corresponding time for reaching the peak heat release rate can be shortened to 218 s and 186 s, respectively, though the peak heat release rate tends to increase to about 241 kW. However, the total heat release rate of the fire flames ejected from the compartment opening were about two to three times larger than that of the free burning in the open space, which implies much greater fire risk. What is more, the heat release rate, the tem- perature distribution of external flames and inner temperature of the compartment gained by numerical simulation proves to be well in ac- cord with the experimental results, though the simulated temperature seems slightly higher, which is likely to be related to the environmen- tal factors of the simulated condition and settings of physical parame- ters in FDS. Furthermore, we have found that the attachment effect of the external flames ejected from the wide openings was more obvious than that of the narrow openings, and in this connection the simula- tion results also prove the same trend.