Steady flows in a naturally-ventilated enclosure containing both a distributed and a localised source of buoyancy

We consider the flows and stratification established in a naturally-ventilated enclosure containing both localised and distributed sources of buoyancy. In this study, both the localised and distributed sources originate from the same horizontal plane, with both adding buoyancy to the enclosure, i.e. representing a point source of heat and a horizontally distributed source of heat at the base of a room. An important parameter controlling the transient and steady states of the enclosure is the ratio of the source buoyancy fluxes ψ=BDBL, with BD and BL the source buoyancy flux of the distributed and localised source, respectively. We examine the role of entrainment between the layers, due to turbulent mixing, and construct a mathematical model to predict the stratification within the room for a range of ψ. We also show that for large ψ and opening areas the two-layer nature of the flow breaks down and there is a short circuit that allows the incoming air to escape through the upper opening without interacting with the full volume of the space. The validity of this model and its break down as predicted by a critical Richardson number are verified against small-scale experiments and the consequences for real-world buildings are discussed.