The hydraulics of exchange flow between adjacent confined building zones

Buoyancy driven flow between two finite zones containing fluid of slightly different density is investigated. The two zones are connected through a common rectangular doorway spanning the channel width so that a two-layer exchange flow develops once the barrier is removed. In the zone that initially contained dense fluid, a buoyant plume of light fluid mixes with the dense fluid leading, over time, to the development of non-trivial ambient density stratification. Meanwhile, dense fluid flows as a gravity current into the zone that initially contained light fluid. This gravity current reflects from the end wall and propagates back toward the opening in the form of an internal bore. When the bore reaches the opening the dynamics of the exchange flow (and consequently the source conditions of the buoyant plume) are substantially altered. Such dynamics are modeled using elements of gravity current, internal bore and plume theory. The flow dynamics of the two zones are linked using two-layer exchange flow theory whereby a maximal exchange flow rate is prescribed only before the bore reaches the opening. The velocity and density jump across the first front decrease substantially once the exchange flow becomes sub-maximal. Depending on the geometrical parameters, the terminal elevation of the first front may lie above, at or below the top of the opening; here, we focus on the former scenario. Experiments have been carried out to validate the model. The comparison between theory and experiment plus the application of the research to architectural fluid mechanics is discussed.