Structure of Wildland Fire Flames

The objectives of this research project are to: perform detailed large eddy simulations (LES) to provide a basic understanding of the structure and dynamics of wildland fire flames; identify the origin of organized vortical structures; evaluate the relative weight of external/wind-driven versus internal/buoyancy-driven motions; evaluate the relative weight of convective versus radiative heat transfer; and provide a companion computational component to the experimental component of the UMD wildland fire research program (led by Prof. Gollner).

Representative stationary flame produced in the UMD wind tunnel

Numerical simulations are being performed with an advanced Computational Fluid Dynamics (CFD) capability, developed by FM Global, and called FireFOAM ( FireFOAM is based on a free, open-source, general-purpose, CFD software package called OpenFOAM ( FireFOAM features state-of-the-art computational mesh generation and physical modeling capabilities, including an object-oriented C++ environment, an ability to handle/generate unstructured polyhedral grids, a compressible flow formulation, advanced LES models and multi-physics models (e.g., to describe turbulence, mixing, pyrolysis, combustion, convective heat transfer, radiative heat transfer, etc), and a massively parallel processing environment (using MPI protocols).

Preliminary test simulations of buoyancy-driven Rayleigh-Taylor instability effects in horizontal thermal boundary layers. Both figures present a top view showing the instantaneous structure of the boundary layer: the external flow is from left to right and the positive buoyant direction is perpendicular to the plane of view, from rear to front. Top figure: moderately unstable boundary layer. Bottom figure: strongly unstable boundary layer.