地铁区间隧道烟气层化现象研究

On the smoke stratification in an interval metro underground tunnel

以重庆某一地铁区间隧道为原型,搭建了1∶15小尺寸隧道试验台,通过小尺寸试验与FDS 6.5.2数值模拟开展隧道顶部烟气温度分布及分层规律研究。基于Newman提出的烟气层分区条件,研究了不同纵向风速下的烟气分层现象,提出了烟气稳定层化长度的概念,并分析了火源热释放速率及断面型式对烟气层化长度的影响。试验证明了Newman提出的烟气分层计算方法是可信的。结果表明：纵向风速较小时,火源下游能呈现烟气分层现象;烟气稳定层化长度受火源热释放速率影响较大,随热释放速率增大而增大;隧道高度的变化对烟气稳定层化长度的影响较小。

The paper intends to conduct some small scale experiments in a 1/15 proportional scale tunnel based on a real metro tunnel case study sample in Chongqing with some CFD simulations conducted by using Fire Dynamics Simulators（ FDS） in a version 6. 5. 2. In the paper,we have made an exploration of the smoke temperature distribution and its stratification moving regularity beneath the tunnel celling through the small scale experiments and CFD simulations. Besides,we have also done a mesh sensitivity study first to propose an optimal computational gird size. Furthermore,we have managed to validate the FDS simulation results in a small-scale model at 4 different fire heat release rates（ HRRs）. And,then,further exploration has been made to work out the smoke temperature distribution situation and the smoke stratification regularity by using the FDS model with the variation of HRRs and the tunnel heights. In accordance with the smoke stratification theory proposed by Newman,we have further examined and worked out the smoke stratification phenomena under the different longitudinal ventilation velocities via the calculation method of smoke stratification proposed by Newman. In addition,we have also proposed the concept of the stable smoke stratification length and analyzed the influence of the fire source HRRs and the tunnel height on the stable smoke stratification distance.The results of our investigation and analysis prove that,smoke stratification phenomena are likely to appear in the downstream region of the fire source when the longitudinal ventilation velocity is usually smaller than the critical one. In addition,the stable smoke stratification distance tends to be reduced while the longitudinal ventilation velocity is increasing. What is more,when the velocity increases to a certain extent,the stable smoke stratification length tends to get decreased to 0,which implies that the smoke stratification tends to decease,which has been confirmed by the observation of our small scale experiment. And,in contrast,the fire HRR may have an important impact on the stable smoke stratification length,which tends to increase with the increase of the size of the fire HRR. Nevertheless,the tunnel height may have just a little influence on the stable smoke stratification.