Study on the effect of obstacles on smoke diffusion and airflow structure in subway stations

Although obstacles exist in every subway station, the impact of obstacles on smoke diffusion characteristics is always overlooked. This work investigates the effect of rectangular obstacles on the ceiling temperature distribution, vertical temperature distribution, and airflow field structure in a subway station fire scenario. Small-scale experiments and numerical simulations are conducted considering varied fire location, heat release rate, blockage ratio, and obstacle location. A dimensionless temperature rise ratio is proposed to quantify the obstacle influence. The key results include (1) Obstacles would cause a proportional decrease in the ceiling temperature rise behind. And the proportion is positively correlated with the blockage ratio but not related to heat release rate, fire location, and obstacle location. (2) The influence of obstacles on vertical temperature rise presents hierarchical characteristics. The same proportional decrease is observed in the smoke layer at the top. As the height decreases in the mixture layer, the temperature rise ratio would also decrease gradually. The air layer at the bottom is kept at a small temperature rise ratio. (3) The wake area behind the obstacle is composed of a recirculation area and a wake recovery area. There is less smoke and slower airflow velocity in the wake area, which means the acquired temperature rise rule is not applicable in this area. A calculation method of the length of the wake area based on the airflow velocity characteristics is presented. This work aims at arousing attention on the influence of obstacles in the fire smoke studies in subway stations.