室内火灾中外部燃烧现象的数值模拟

CFD Simulation of the External Burning in the Compartment Fire

外部燃烧是室内火灾中火焰随烟气流出窗户并在窗户外燃烧的现象。外部燃烧会造成火势从初始着火的房间向其他房间或楼层蔓延,具有很大的危害性。本文应用美国国家标准技术局(NIST)开发的FDS程序,对外部燃烧现象进行了研究。首先对Bullen和Thomas的实验进行数值模拟,用以验证FDS对外部燃烧现象的模拟效果。在相近的燃料过量因子的条件下,计算得到的外部燃烧羽流的温度分布结果、外部燃烧火焰的高度和火焰距离窗户所在壁面的水平距离与Bullen和Thomas的实验结果符合得较好。之后,研究了不同窗户大小和不同燃料消耗率对外部燃烧的影响。最后,发现当燃料消耗率足够大致使室内燃料过量因子接近1时,室内火焰将会熄灭,燃料流出窗户形成的外部燃烧火焰会被拉长,火焰紧贴窗户外的壁面向上燃烧。

External burning is the spread of the un-burning fuel of the compartment fire via the openings of the room and burning out of the openings. The risk of the phenomena is great because it will cause the secondary fires and cause the spread of the fire from the origin room to other rooms. The purpose of this work is to investigate the external burning using the Fire Dynamics Simulator （FDS） code developed by the Building and Fire Research Laboratory at the National Institutes of Standards and Technology （NIST）, US. First FDS code is verified by simulating the external burning experiments of Bullen and Thomas. The numerical results of the contours of the external temperature, the height of the flame and the distance of the flame tip to the fa ade accord well with the experiments＇ results at the similar excess fuel factor. Secondly, the effects on external burning flame of the window＇s shape and the fuel mass loss rate are studied. When the fuel mass loss rate is large enough so that excess fuel factor in the room is dose to 1, the fire in the compartment would be extinguished and the external burning flame would be elongated and spread along the fa ade wall.