排烟口间距对隧道集中排烟烟气层吸穿影响的模拟

Effect of extraction vent distance on smoke layer plugholing under central extraction system in tunnel

吸穿现象的发生将降低隧道集中排烟效率。排烟口间距是影响烟气层吸穿的重要因素。以长22 m的1∶20缩尺寸集中排烟隧道模型为数值模拟研究对象。采用对称方式开启6个排烟口进行双向均衡排烟模式。比较了排烟口间距分别为3 m和2 m时的烟气蔓延范围、烟气层温度和厚度,分析了烟气层厚度、温度与排烟速率之间的关系。结果表明:排烟速率大到一定程度时会导致烟气层吸穿;排烟口间距越大,导致排烟口开始发生吸穿的排烟速率越小;同一排烟速率下,排烟口之间的间距越大,越远离火源的排烟口越容易发生吸穿。因此,为避免吸穿现象的发生,需选取合适的排烟速率及排烟口间距。

The occurrence of smoke layer plugholing will lead to the decrease of the efficiency of the mechanical extraction system. The extraction vents distance is one of the important factors which have can result in plugholing occurrence under central extraction system in tunnel. To confirm the effect of extraction vent distance on smoke layer plugholing under central extraction system in tunnel, we have applied a computer model with FDS. The numerical mode was con- strueted on the base of a 22 m-length with 1：20 scale tunnel model of central smoke extraction system. Two extraction vent distances of 2 m and 3 m were simulated. And six vents were set to be opening sym- metrically in the central smoke extraction mode. At the same time, 26 working conditions were simulated in the range of 0. 045 -0. 179 m3/s with different extraction rates. The smoke spread, temperature distribution and depth of the smoke layer below the extraction vents were analyzed. The variations of the temperature and depth under dif- ferent exhaust rates were quantitatively described. The results show that plugholing occurs in two extraction vent distances when smoke exhaust rate increases to some relative high levels. A different range of smoke exhaust rates result in plugholing occurrence under the dif- ferent distances of extraction vent. The results also indicate within the same smoke exhaust rate, the plugholing could occur in advance in the vents which is farther away from fire resource when the distance of extraction vents increases. Additionally, the relationships for quanti- tatively descripting of the smoke exhaust rate and smoke layer depth, temperature and smoke exhaust efficiency respectively are presented to observe the range of smoke exhaust rate when plugholing occurs in different distance of extraction vents, in order to provide the reference to optimize the central extraction system design.