A numerical study on the multiple steady states of buoyancy ventilation in underground buildings

For temperature control and smoke extraction of underground space, studying buoyancy ventilation seems to be essential.However, buoyancy driven ventilation in deep underground spaces were seldom reported in existing research papers. Some underground spaces have unique properties such as their deep location, with installed vertical channels of several hundred meters in length, raising the potential to rely on buoyancy driven ventilation only. This paper has described the results from one study focused on such deep space with high intensity of heat sources. The phenomenon studied in this paper concerns the way that different steady states of flow and temperature can establish themselves. The study was done by numerical simulation, including multiple factors, such as initial condition, the intensity and the location of heat source, were considered. The aim was to identify the final steady states under different situations. It has been well justified that the dominant flow tends to follow the expansion of local thermal plume. This trend, however, may change with different initial velocities, leading to alternative steady states.