Plumes and jets in semiconfined spaces

Laboratory experiments and theoretical analysis of the stratification and the flow patterns due to the presence of plumes or jets in semi-confined regions are presented. Three topics, flow patterns in two prototype geometries and penetrative entrainment by a turbulent fountain in a two-layer stratification environment, are investigated. The first study concerns natural ventilation between two connected spaces, in which a mathematical model of a single room is extended to the case of two chambers of equal height connected by two openings. The flow between the two chambers is driven by a single source of buoyancy in one of the chambers. Individually, both chambers have displacement ventilation in this geometrical arrangement. The two chambers have a tune-dependent interaction and the timescale depends on the size of the larger space. The second study concerns a new experiment to measure the penetrative entrainment by a turbulent fountain in a steady two-layer stratification environment. A theoretical model was established by assuming that the stratification consists of two uniform layers and the entrainment rate is estimated quantitatively by three formulae. Two quasi-uniform layers in the steady state were observed in the laboratory experiments. Experimental results gave a nearly constant penetrative entrainment rate (0.8 ± 0.2) across a density interface when the local Richardson number is smaller than 1. This penetrative entrainment rate is larger than those reported in previous studies. The third study concerns the flow driven by a single source of buoyancy and a single cooling diffuser in a ventilated space. This study is related to a newly emerging strategy in air-conditioned cooling design, an underfloor air distribution system. A new model for the flow in this specific space was proposed and laboratory experiments were carried out to simulate the flow. The model is based on plume theory and a fountain model of the steady-state two-layer stratification in a ventilated room. The dominant parameters are shown to be the buoyancy flux of the heat source, and the volume and momentum fluxes of the cooling diffuser. The results provide input on improvement of the current ventilation strategies.