烟囱效应作用下火灾烟气蔓延规律模拟

Simulation study on the law of fire smoke propagation under the stack effect

为研究高层建筑火灾烟囱效应产生后的烟气蔓延规律,基于FDS火灾模拟软件,以某高层建筑为例,对比分析了4种不同横截面尺寸竖井烟气蔓延特性,引入竖井无量纲长径比判断烟囱效应明显与否,研究了烟囱效应的产生特征及其烟气蔓延规律,分析了建筑中性面之上楼层的温度、CO体积分数和能见度变化。结果表明:无量纲长径比在8左右时竖井内烟气流速发生突变,竖井内大部分区域烟气流速达到6 m/s,产生明显的烟囱效应;中性面以上的楼层受烟气危害远大于中性面以下,且烟气在中性面以上的水平蔓延速度随层高增加而不断加快;随着火势发展,中性面之上疏散走道温度均超过了安全疏散的临界温度60℃,距离火源越远的楼层CO体积分数达到临界值的速度越快。研究为高层建筑火灾的防排烟设计和人员疏散条件的确定提供了理论依据。

In order to study the law of smoke propagation caused by stack effect in high-rise buildings,the smoke spread characteristics of four different cross-section dimensions(CSD)of vertical shaft in a high-rise building were compared and analyzed based on FDS.Aspect ratio of the shaft was introduced to judge whether the stack effect phenomenon was obvious or not.The laws of smoke longitudinal spread time and smoke velocity in shaft were obtained.A shaft with aspect ratio of 11.8 is selected to study the generation characteristics of the stack effect and its influence on the distribution of smoke.The temperature,CO volume fraction and visibility changes of the floors above the neutral plane of the building were analyzed.Simulations illustrated that in the case of 8 MW fire on the first floor of the building,when aspect ratio is around 8,the smoke velocity in the shaft has a sudden change,and the smoke velocity in most areas of the shaft reaches 6 m/s,resulting in an obvious stack effect;the smoke hazards of floors above the neutral plane are much greater than those below the neutral plane under stack effect.The horizontal spread speed of smoke above the building neutral plane accelerates with the increase of floor height.As the fire situation develops,the temperature of the evacuation corridor above the neutral-plane all exceeds the critical temperature of the safe evacuation by 60℃.The further away from the fire,the faster the CO volume fraction reaches the critical value.The change of visibility decreases sharply.The time to reach the critical visibility at the shaft mouth of each floor is similar,and the time to reach the critical visibility at the end of the walkway decreases gradually with the increase of building height.