环境风条件下非对称街道峡谷的火灾烟气扩散与回卷机制  

Fire smoke diffusion and recirculation mechanism in an asymmetric street canyon under ambient wind conditions

作　　者：陆凯华 向燕晴 徐华升 毛少华 李博[1] 倪晓阳[1] LU Kaihua;XIANG Yanqing;XU Huasheng;MAO Shaohua;LI Bo;NI Xiaoyang(Faculty of Engineering,China University of Geosciences(Wuhan),Wuhan 430074,China)

机构地区：[1]中国地质大学(武汉)工程学院,湖北武汉430074

出　　处：《安全与环境工程》2024年第5期80-86,94,共8页Safety and Environmental Engineering

基　　金：国家自然科学基金项目(52076199)。

摘　　要：城市中常见多种街道峡谷(简称“街谷”)结构,一旦发生火灾,易形成大量火灾烟气等有害气体。受城市冠层环境风的影响,烟气向下风向倾斜,有可能被下风向建筑物阻挡而无法顺利向自然环境中扩散,导致出现街谷内烟气回卷现象,对身处其中人员的安全疏散和身体健康十分不利。运用火灾计算流体模拟软件FDS,重点考虑街谷非对称性对火灾烟气扩散的影响效应构建了街谷模型;选取典型的街谷条件,通过改变上、下风向建筑物高度和环境风速,揭示了烟气扩散与流场结构演化特征,获得了各非对称街谷条件下的临界回卷风速;引入街谷非对称因子m(上、下风向建筑物高度之比),建立了临界回卷风速与非对称因子m之间的预测模型。结果表明:保持下风向建筑物高度不变而增加上风向建筑物高度时,烟气扩散呈现完全回卷、半回卷和不回卷三阶段控制,反之,保持上风向建筑高度不变而增加下风向建筑物高度时,烟气扩散呈现不回卷和完全回卷两阶段控制;m值越大,即上风向建筑物越高或下风向建筑物越低时,越难形成烟气回卷现象,所对应的临界回卷风速也越大,而m值相近时街谷火灾烟气回卷行为相似;最终提出了临界回卷风速vc与街谷非对称因子m之间的分段线性预测模型。Various street canyon structures are commonly observed in urban cities,and once a fire occurs,a large amount of harmful gas such as fire smoke is generated.Affected by the ambient wind,such fire smoke may tilt to downstream direction.The fire smoke may be obstructed by a leeward building so that it can not fully disperse to surrounding,resulting in the smoke recirculation inside the street canyon,which is very detrimental to the safe evacuation and physical health of personnel there.This article applied the CFD fire simulation software FDS to construct a street canyon model,focusing on the effect of street canyon asymmetry on the fire smoke diffusion.By selecting typical street canyon conditions,changing the windward or leeward building height and ambient wind velocity,the evolution characteristics of fire smoke diffusion and flow field structure were indicated,and the critical recirculation wind velocity for each asymmetric street canyon condition were obtained.A factor of m,defined as the ratio of the windward building height to leeward building height,was introduced for the description of the street canyon asymmetry,and the prediction model between the critical recirculation wind velocity and the street canyon asymmetry factor was proposed.The results show that while maintaining the leeward building height but increasing the windward building height,the smoke diffusion exhibits three different stages,i.e.,fully recirculation,semi-recirculation,and non-recirculation stages;on the contrary,while maintaining the windward building height but increasing the leeward building height,the smoke diffusion exhibits two different stages,i.e.non-recirculation,and fully recirculation stages.It is found that with the increasing value of m,corresponding to a higher windward building height or leeward building height,the smoke recirculation is more unlikely to be formed,in that the critical wind velocity relative to the occurrence of smoke recirculation will be greater.When the factor of m is close,the smoke recirculation beha

关 键 词：街道峡谷 非对称因子 烟气扩散 环境风 临界回卷风速 

分 类 号：X932[环境科学与工程—安全科学]