Forest canopy sub-layer turbulence and atmospheric coupling in a wildland fire model

Empirical and semi-empirical models of wildland fire spread and fuel moisture have been in use for several decades. Such models incorporate meteorological data to predict fire intensities, rates of spread and smoke production, but, for practical reasons, the effects of these outputs on the atmosphere are not considered. However, realistic simulations of the interplay between fire and atmosphere are necessary to explore the self-modifying effects of wildland fire, the dispersion of smoke by forest canopies, the influence of canopy fluxes on fuel moisture, and to simulate the dynamics of fire at wildland-urban interfaces (WUI). Fortunately, a new generation of physical, CFD-based wildland fire models is being developed that will provide insight into fire-atmosphere interactions.

Using the National Institute of Standards and Technology's WUI-Fire Dynamics Simulator (WFDS), we examined the effects of simulated forest canopies on wind-driven turbulence below, within and above the canopy. Here, we compare vertical profiles of shear stress, mean velocity and statistical moments from WFDS simulations with published experimental data from an open-channel flume containing vertical-element canopies of uniform height and varying density. In addition, we present initial results from simulations of the effects of simple "block" and more realistic heterogeneous forest canopies, created with the WFDS fuel element model, on fire dynamics and turbulence statistics.