Numerical study on the airflow characteristics and smoke control condition in stair area of subway stations

As the key facility connecting different floors in subway stations, the smoke control in the stair area has been one of the most important goals of fire protection design. But the detailed airflow field and smoke spread process are rarely discussed. With numerical simulation, this work investigated the airflow velocity distribution and critical condition for smoke control in two critical openings of the stair area, which include the opening beneath the ceiling screen and the opening on the top of the stair. The results indicate that (1) In spatial dimension, the airflow velocity distribution shows a nonuniformity within each opening and a difference between two openings. (2) In the temporal dimension, the airflow velocity shows a normal distribution characteristic. The strong turbulence leads to a dynamic airflow field with an unstable smoke spread process. (3) For the critical opening beneath the ceiling screen, the airflow velocity is dominated by thermal buoyancy or inertia force in different areas. The practical smoke control criterion is to ensure the smoke layer is higher than the edge of the ceiling screen. (4) For the critical opening on the top of the stair, airflow velocity shows an exponential decay distribution. The critical condition could be predicted with a virtual fire source within the stair. This work hopes to present the necessity of dynamic and microscopic modeling of the airflow - smoke flow interaction for an accurate prediction of the smoke control condition in the stair area of subway stations.