High-resolution numerical models for smoke transport in plumes from wildland fires
A high-resolution large-eddy simulation (LES) model is employed to examine the fundamental structure and dynamics of buoyant plumes arising from heat sources representative of wildland fires. Herein we describe several aspects of the mean properties of the simulated plumes. Mean plume trajectories are apparently well described by the traditional two-thirds law for plume rise; however, the spatial structure of the mean plume is significantly different from the Gaussian distributions typically assumed in simple plume models. This discrepancy arises from the fact that entrainment properties of a buoyant plume in a cross wind are significantly different from those of a buoyant plume in the absence of a cross wind, a result of the interaction of the buoyancy-generated vorticity in the plume with the vorticity in the ambient wind. The depth of the crosswind shear layer at the surface also appears to play a role in both the horizontal and vertical spread of the plume boundaries downwind, and in particular the increase in horizontal spread acts to increase the departure from a Gaussian distribution seen in the plume cross sections.