Computational Study on the Influence of Obstacle Geometry Within a Compartment on Backdraft Intensity

A computational analysis using the Fire Dynamics Simulator (FDS) was performed to compare backdraft intensity according to the geometric shapes of obstacles within a compartment. Four obstacle configurations (two cubic blocks, a rectangular block, a stair-shaped obstacle, and three vertical plates) were installed within compartments with a vertical door-type opening (door) and a horizontal slot-type opening (slot), and their effects on backdraft intensity were investigated and compared. The gravity current travel time to the rear wall, determined from the oxygen mass fraction distribution, was the shortest in the cases without obstacles for both opening configurations. In addition, the door opening condition generally exhibited shorter gravity current travel times than the slot opening condition because of the higher incoming airflow velocity. The obstacles altered the propagation path and leading-edge structure of the gravity current, thereby affecting the mixing of unburned gases and air. During backdraft events, the peak overpressure inside the compartment and the peak heat release rate exhibited a strong linear relationship, confirming that backdraft intensity is closely related to rapid heat release. In contrast, no clear correlation was observed between the peak overpressure and either the global equivalence ratio or the amount of incoming oxygen. These results indicate that, in compartments containing obstacles, backdraft intensity may be influenced more strongly by other factors, such as internal flow structures and local mixing conditions, than by the global equivalence ratio or simply the amount of incoming oxygen.