Abstr:Confined buoyant plume
Underlying Flow Regime 4-09
Buoyant plumes within confined spaces are an important generic component of air flows in buildings. Such plumes occur whenever there is a heat source at low level – for example, a person, equipment or sun-patch. The heated air rises from the thermal source to produce a plume of warm air that rises within the space. On reaching ceiling level, the buoyant air will spread out laterally to form a warm layer. The principal of displacement ventilation is to maintain the level of this warm layer above the level of occupation. This enables comfort conditions to be maintained in the occupied zone without the need to condition the whole of the space.
The dynamics of thermal plumes play a central role in displacement ventilation, through impact on:
- temperature and pollutant distributions
- ventilation supply air temperature and volume flow rate requirements
- buoyancy-driven natural ventilation rates
In order to optimise the performance of displacement systems it is desirable to model the buoyancy-driven air flows associated with thermal plumes, typically along-side the other environmental factors affecting the thermal dynamics of the space, such as solar gain to room surfaces, distribution of occupants and heat sources, and conduction of heat through room fabric.
This UFR focuses on the contribution of the plume dynamics to these flows. Turbulent plumes are a challenging flow to model using CFD. It is fundamental, therefore, to ensure that this basic ‘building block’ of buoyancy-driven flow is modelled correctly. The situation considered here is a simple and robust one, consisting of a single plume in a box with low-level supply and high-level extract. The situation is an attractive one for the UFR as it presents a steady-state flow for which recent CFD work has been carried out and successfully compared to both experiment and theory.
This UFR is also of particular relevance to UFR1-03 Buoyant plumes.
Contributors: Jake Hacker - Arup