Modeling buoyant plumes: Fundamentals and applications

The structure and dynamics of buoyant plumes arising from isolated heat sources representative of wildland fires are examined using a large-eddy simulation (LES) model. Despite the fact that buoyant plumes have been studied extensively in many wide-ranging contexts, well-resolved numerical simulations of thermal plumes are still somewhat rare, and a detailed understanding of the turbulent dynamics of buoyant plumes remains elusive. The basic structure and behaviour of the simulated plumes will be presented, along with the dependence of this structure and behaviour on parameters such as the speed of the ambient cross flow and the intensity of the heat source. Results from the LES model illustrate the role and significance of coherent vortices in plume dynamics. Indeed, in the presence of an ambient atmospheric flow, several types of vortical structures may be identified that dominate the structure and behaviour of the plume.

In addition to its use in addressing the fundamental structure and dynamics of buoyant plumes, the LES model has been applied to several problems that are motivated by observed cases of fire and plume behavior. Such applications include (i) the interactions between buoyant plumes and density currents (associated, for example, with sea-breeze fronts, thunderstorm outflows, and intense cold fronts), and (ii) the development of pyrocumulonimbi and tornadoes associated with large, intense fires. The insights into these problems provided by the model will be discussed, along with the potential for further applications using the model.