@article {bnh-6830, title = {Simulation of flows through canopies with varying atmospheric stability}, number = {562}, year = {2020}, month = {04/2020}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

Large eddy simulation is performed of a flow through forest canopy over a range of atmospheric stabilities. A heat source is introduced at the top of the tree canopy to model the heating of canopy top by solar energy, Unlike our previous report [1] where an ideal Monin-Obukhov method was used for the surface heat flux variation, this study has introduced a varying volumetric heat flux in a sub-canopy region. The flow field develops naturally with the applied thermal stratification and pressure-driven flow. The forest canopy modelled using the leaf area density (LAD) of pine trees. The simulation is allowed for a sufficient time, of the order of 20000 s, to adjust with the applied heat flux in the domain. The simulation is attempted for two broad classes: stable and unstable situations with varying negative and positive fluxes, respectively. The simulation results are validated against the numerical study of Nebenfuhr et al. [2] and the field measurement taken at Ryningsnas, Sweden [3]; which shows a good agreement. The effect of canopy top heat flux on different atmospheric stabilities are studied in detail and we present mean velocity and Reynolds stresses. These results suggest that atmospheric stability may affect the rate of spread and pollution dispersion, especially in the case of unstable stratifications. There is a need to understand atmospheric stabilities for accurate analysis of wildland fire spread and fire intensity. Most importantly, flame characteristics must be carefully diagnosed with due account for different atmospheric conditions prevailing in real wildland fire for reducing property damage and loss of lives.

}, keywords = {atmospheric boundary layer, forest canopy, thermal stratification, turbulence, turbulent kinetic energy}, issn = {562}, author = {Nazmul Khan and Duncan Sutherland and Khalid Moinuddin} } @article {bnh-6046, title = {Simulation study of grass fire using a physics-based model: striving towards numerical rigour and the effect of grass height on the rate of spread}, journal = {International Journal of Wildland Fire}, volume = {27}, year = {2018}, month = {11/2018}, pages = {800-814}, abstract = {

Grid-independent rate of spread results from a physics-based simulation are presented. Previously, such a numerical benchmark has been elusive owing to computational restrictions. The grid-converged results are used to systematically construct correlations between the rate of spread (RoS) and both wind speed and grass height, separately. The RoS obtained from the physics-based model is found to be linear with wind speed in the parameter range considered. When wind speed is varied, the physics-based model predicts faster RoS than the Mk III and V (McArthur) models (Noble\ et al.\ 1980) but slower than the CSIRO model (Cheney\ et al.\ 1998). When the grass height is varied keeping the bulk density constant, the fire front changes from a boundary layer flame mode to plume flame mode as the grass height increases. Once the fires are in plume mode, a higher grass height results in a larger heat release rate of the fire but a slower RoS.

}, keywords = {atmospheric boundary layer, operational model, Physics-based modelling, wildland fire, wind speed}, doi = {https://doi.org/10.1071/WF17126}, url = {http://www.publish.csiro.au/wf/WF17126}, author = {Khalid Moinuddin and Duncan Sutherland and William Mell} }