Numerical Investigation of External Wind Effect on Smoke Characteristics in a Stairwell

Fire-induced smoke is the most lethal threat to the residents in high-rise buildings and it is necessary to understand the smoke rising characteristics for the engineering applications of smoke control system. Previous researches only focused on smoke movement driven by buoyancy and stack effect. It is common, however, that external wind can flow inside the building through broken windows and affect the smoke flow. This paper studies the influence of external wind on smoke characteristics in a stairwell. A series of simulations were conducted in a full-scale staircase with top window open. The ambient wind velocity ranged from 0 m/s to 6 m/s and the heat release rate varied from 500 kW to 1500 kW. Results show that the rise time for plume reaching a given height increases with the wind velocity. For a HRR, smoke cannot overcome the wind force when wind velocity exceeds a critical value. Thus a quantitative model is proposed to predict the rise time of plume front considering the hindrance of wind. Moreover, the mass flow rate at the bottom door decreases with wind velocity due to pressure attenuation. However, the CO concentration increases by about 15% with wind velocity, which is a great danger to trapped victims.