Computational investigation of flame characteristics of a non-propagating shrub fire

A three-dimensional multiphase, physics-based model based on large eddy simulation methodology was used to investigate a model shrub fire at a statistically stationary state. Governing equations of the solid phase were modified to achieve this state at which a detailed analysis of the flame and plume is possible through time averaging. The computations were performed for shrub bulk densities ranging from 1 to 6kg/m3 and corresponding time-averaged flame heights were recorded. The continuous flame zone, intermittent flame zone and thermal plume region were identified. It was found that flame height scales as the two-fifth power of heat release rate for a mean flame tip temperature of 800K. The slopes of temperature and velocity profiles along the centerline in the continuous and thermal plume region were consistent with the corresponding slopes for buoyant diffusion flames over porous burners. First-order and second-order statistics were investigated and it was found that there is a strong correlation between velocity and temperature in the continuous flame region. This strong correlation was attributed to the strong buoyancy accelerations due to combustion of pyrolysis gases from the shrub. Investigation of vortical structures formed in the fire plume showed that strain dominates the flow in the continuous flame region with large scale vortices forming downstream in the plume region. •Physics-based LES investigation of a statistically stationary shrub fire.•Statistical analysis of velocity and temperature variables through time-averaging.•Various bulk density values considered.•Average flame heights calculated as a function of heat release rate.•Strong correlations observed between the velocity and temperatures in the continuous flame region.