@article {bnh-8367, title = {Simulated behaviour of wildland fire spreading through idealised heterogeneous fuels}, journal = {International Journal of Wildland Fire}, year = {2023}, month = {02/2023}, abstract = {

Homogeneous vegetation is widely used in wildland fire behaviour models, although real vegetation is heterogeneous in nature and composed of different kinds of fuels and non-combustible parts. Many features of fires can arise from this heterogeneity. For land management and firefighting, creating heterogeneous fuel areas may be useful to reduce fire intensity and rate of spread (ROS), and alter fire geometry. Recently, an empirical model for fire spread in spinifex grasslands was developed and validated against experimental measurements. In this study, physics-based grassland fire behaviour simulations were conducted with varying percentages of fuel cover and alternating square and rectangular patches of burnable and non-burnable material. The environmental conditions and thermophysical properties of the grassland were kept constant throughout the simulation to separate the effects of fuel heterogeneities from other parameters. For three sets of nominal wind velocities, 3, 5.6 and 10 m s-1, we identified {\textquoteleft}go{\textquoteright} and {\textquoteleft}no go{\textquoteright} fires. Reasonable agreement between the non-dimensionalised simulated ROS and observed ROS in spinifex was found. There is a significant reduction of fire intensity, ROS, flame length, fire width and fire line length due to the heterogeneous effect of vegetation.

}, keywords = {fire line length, flame length, heterogeneity, homogeneous vegetation, Rate of spread, spinifex, wildland fire, wind spee}, doi = {https://doi.org/10.1071/WF22009}, url = {https://www.publish.csiro.au/wf/WF22009}, author = {Nazmul Khan and Duncan Sutherland and Khalid Moinuddin} } @article {bnh-8303, title = {Initial growth of fires in eucalypt litter, from ignition to steady-state rate of spread: laboratory studies}, journal = {International Journal of Wildland Fire}, year = {2021}, month = {12/2021}, abstract = {

As part of an investigation of wildfire growth and acceleration, the initial growth of incipient fires burning in uniform dry eucalypt forest (Eucalyptus rossii,\ E. macrorhyncha) litter fuel of 1.2 kg m-2\ was studied in a combustion wind tunnel with a fuel bed width of 1.5 m. Fifty-eight fires of three ignition patterns (point, 400-mm line and 800-mm line) were carried out at two air speeds (1.25 and 2.0 m s-1) and two dead fuel moisture content (FMC) groups for each air speed (<=7.5\% and \>7.5\% oven-dry weight for the low air speed and <=5\% and \>5\% for the high air speed). The fraction of steady-state rate of spread reached as a function of time was determined and fitted to two theoretical fire growth models from the literature. The best model suggests the times for a point ignition fire to reach steady-state spread rate were ~38 and 50 min under the higher FMC for 2.0 m s-1\ and 1.25 m s-1\ air speeds, respectively, and ~25 min under the lower FMC for 2.0 m s-1. Future work will extend these results to field-scale fire behaviour, which will help improve operational response to wildfire outbreaks and planning of ignition patterns for prescribed burning.

}, keywords = {acceleration, combustion wind tunnel, experiments, Fire behaviour, fire development, fire growth, Pyrotron, Rate of spread}, doi = {https://doi.org/10.1071/WF21094}, url = {https://www.publish.csiro.au/WF/WF21094}, author = {J.S. Gould and Sullivan, Andrew} } @article {bnh-6642, title = {A report on WRF software development (preliminary)}, number = {539}, year = {2020}, month = {01/2020}, institution = {Bushfire \& Natural Hazards CRC}, address = {Melbourne}, abstract = {

Bushfire is one of the major natural hazards Australia encounters every year because of its dry weather and widespread bushlands. During the dry season, occurrence of simultaneous bushfires at different locations is quite common. The fire management authorities face challenges on deployment of resources (human and other logistics) properly to mitigate multiple bushfires. To prioritize, they depend on the modelling of real-time behaviours of the fire under consideration. Fire rate of spread (RoS) is one of the most important parameters that the authority wants to determine before proceeding to resource allocation. RoS during forest fire can be slowed by reduced sub-canopy wind. In operational models, it is accounted by a parameter, wind reduction factor (WRF). Current values used as WRF are not based on science. In this work, we are presenting a software (preliminary version) that can calculate WRF scientifically. We apply a dynamic WRF obtained from a mathematical model in an operation model, Spark. This will lead to better prediction of RoS, once fully implemented.

}, keywords = {Bushfire, fire management, model, Rate of spread, software development}, issn = {539}, author = {Mahmood Rashid and James Hilton and Nazmul Khan and Duncan Sutherland and Khalid Moinuddin} } @article {bnh-6045, title = {Modelling of tree fires and fires transitioning from the forest floor to the canopy with a physics-based model}, journal = {Mathematics and Computers in Simulation}, year = {2019}, month = {06/2019}, abstract = {

Wildland fires can take different forms such as surface fire or an elevated crown fire or combination of both. Crown fires are normally originated from surface fires spreading either along the bark of the tree trunks or direct flame contact to low branches with leaves and needles. In the past, surface fire (grassfire) spread simulations were conducted using physics-based models with fidelity. Here, we firstly seek numerically converged results for the burning of a single tree. Previously, numerical convergence for such physics-based fire simulations has been elusive. Subsequently, the linear and Arrhenius thermal degradation sub-models are appraised. For both thermal degradation sub-models grid convergence of the mass-loss rate is achieved with a 50\ mm grid. The grid converged simulations also agree with experimental results of a single burning Douglas fir tree. A fire in a modelled tree plantation is then simulated using the linear thermal degradation sub-model. The aim of this part is twofold: one to demonstrate a good modelling practice; and secondly to assess the model capability to simulate transitioning from a forest floor fire to a crown fire leading to a quasi-steady rate of spread. The Kolmogorov{\textendash}Smirnov test is used to rigorously demonstrate that the simulations on different grid and domain sizes have converged {\textemdash}\ that is, the results have become independent of the numerical parameters imposed upon the simulation.

A physics-based model reproduces many observed features of surface fire to forest fire transition. The crown fire propagates with a quasi-steady rate-of-spread after an initial development period. Analysis of the volumetric heat release rate shows that a surface fire propagates under the crown fire and supplies energy to support the burning of the crown. Overall many features are qualitatively in agreement with other tree and crown fire studies.

}, keywords = {Crown fire, Fire transition, Physics-based modelling, Rate of spread, Tree fire}, doi = {https://doi.org/10.1016/j.matcom.2019.05.018}, url = {https://www.sciencedirect.com/science/article/abs/pii/S0378475419301995}, author = {Khalid Moinuddin and Duncan Sutherland} }