@article {bnh-8377, title = {Implementation of spatially-varying wind adjustment factor for wildfire simulations}, journal = {Environmental Modelling \& Software}, volume = {163}, year = {2023}, month = {05/2023}, pages = {105660}, abstract = {

The behaviour and rate of spread of a wildfire is strongly affected by local wind conditions depending on topography and surrounding vegetation. The wind speed within dense vegetation can be substantially lower than the open wind speed above the vegetation. This is commonly accounted for by applying a local correction factor to the local wind speed which can be called the wind adjustment factor (WAF). WAFs are often difficult to calculate and are usually based estimates for a particular vegetation type. Variation in the vegetation may result in spatially varying WAFs. We implement a model for spatially-varying WAFs based on leaf area index (LAI) and vegetation height data, which can be derived from remote sensing data sources. The model is implemented within Spark an operational wildfire prediction framework. Simulations of historical fires using the spatially-varying WAF model generally provided improved predictions compared to recorded fire extents than simulations without a spatially-varying WAF.

}, keywords = {Bushfire, modeling, spread, WAF, Wildfire, wind adjustment factor}, doi = {https://doi.org/10.1016/j.envsoft.2023.105660}, url = {https://www.sciencedirect.com/science/article/abs/pii/S1364815223000464?dgcid=coauthor}, author = {Duncan Sutherland and Mahmood Rashid and James Hilton and Khalid Moinuddin} } @article {bnh-8366, title = {Physics-based modelling of junction fires: Parametric study}, journal = {International Journal of Wildland Fire}, year = {2023}, month = {02/2023}, abstract = {

Background; Junction fires occur when two fire fronts merge. The ROS and HRR of the junction quickly increase more than that of each fire front; this effect is exacerbated by slopes. Aims; Numerical modelling of junction fires and an interpretation of their behaviour is given by examining the key factors that influence the fires. Methods; Physics-based simulations of laboratory-scale junction fires were performed for shrub fuel bed using FIRESTAR3D. Twenty cases were simulated to quantify the effect of slope (0{\textdegree} to 40{\textdegree}) and junction angles (15{\textdegree} to 90{\textdegree}). Key results; Accelerative and decelerative behaviours were observed for junction angles lower than 45{\textdegree}, but above this, deceleration was absent. The behaviour was firmly related to junction angle evolution which controlled the flame and the interactions between fire fronts. HRR followed similar trends; maximum HRR increased with increasing junction angle. Convection was found to be the primary heat transfer mode in the initial propagation phase. In non-slope cases, radiation was the dominant method of heat transfer, but convection dominated fires on slopes. Conclusions; The physics-based model provided great insight into junction fire behaviour. The junction angle was critical for determining ROS and fire behaviour. Implications; The research helped to assess the effects of some topographical parameters in extreme fires. Situational awareness, operational predictions, and firefighter safety will consequently improve.

}, keywords = {fire behavior, physics-based model}, url = {https://www.publish.csiro.au/WF/justaccepted/WF22121}, author = {Ahmed Hassan and Gilbert Accary and Duncan Sutherland and Khalid Moinuddin} } @article {bnh-8372, title = {Physics-based simulations of grassfire propagation on sloped terrain at field scale: flame dynamics, mode of fire propagation and heat fluxes}, journal = {International Journal of Wildland Fire}, year = {2023}, month = {01/2023}, abstract = {

The interaction of wind and fire on a sloped terrain is always complex owing to the mechanisms of heat transfer and flame dynamics. Heating of unburned vegetation by attached flames may increase the rate of spread. The relative intensities of convective and radiative heat fluxes may change fire behaviour significantly. This paper presents a detailed analysis of flame dynamics, mode of fire propagation and surface radiative and convective heat fluxes on sloped terrain at various wind speeds using physics-based simulations. It was found that with increasing slope angles and wind velocity, the plume inclines more towards the ground and becomes elongated in upslope cases, whereas in downslope cases, the plume rises from the ground earlier. For higher wind velocities, the flame and near-surface flame dynamics appear to show rising, even though the plume is attached. The flame contour results indicate that the near-surface flame dynamics are difficult to characterise using Byram{\textquoteright}s number. A power-law correlation was observed between the simulated flame lengths and fireline intensities. The convective heat fluxes are more relevant for wind-driven fire propagation and greater upslopes, whereas both fluxes are equally significant for lower driving wind velocities compared with higher wind velocities.

}, keywords = {Byram number, fire propagation, flame, grassfire, heat fluxes, plume, rate of spread (RoS), slope, wind velocity}, doi = {https://doi.org/10.1071/WF21125}, url = {https://www.publish.csiro.au/wf/WF21125$\#$FN1}, author = {Jasmine Innocent and Duncan Sutherland and Nazmul Khan and Khalid Moinuddin} } @article {bnh-8375, title = {Physics-based simulations of grassfire propagation on sloped terrain at field scale: motivations, model reliability, rate of spread and fire intensity}, journal = {International Journal of Wildland Fire}, year = {2023}, month = {01/2023}, abstract = {

This study focuses on physics-based modelling of grassfire behaviour over flat and sloped terrains through a set of field-scale simulations performed using the Wildland{\textendash}urban Interface Fire Dynamics Simulator (WFDS), with varying wind speeds (12.5, 6 and 3 m s-1) and slope angles (-30{\textdegree} to +30{\textdegree}). To ensure the accuracy of this Large Eddy Simulation (LES), a sensitivity study was carried out to select the converged domain and grid sizes. Fire isochrones, locations of fire front, dynamic and quasi-steady rates of spread (RoS), and fire intensity results from the simulations are presented. Within the simulations conducted, the RoS and fire intensity were found to be higher with increasing slope angles, as well as with wind velocity. RoS comparisons are made with various empirical models. At different slope angles and driving wind velocities, different empirical quasi-steady RoS broadly match with particular dynamic maximum, minimum and averaged RoS values from this study. It appears that the ideal nature of grassfire propagation simulation and challenges related to measuring quasi-steady values in experimental studies are likely reasons for the observed differences. Additionally, for lower wind velocities, the RoS{\textendash}fire intensity relationship (Byram{\textquoteright}s) deviates from linearity for greater upslopes.

}, keywords = {Fire behaviour, fire front, grass fire, intensity, rate of spread (RoS) of fire, simulations, slope, wind speed}, doi = {https://doi.org/10.1071/WF21124}, url = {https://www.publish.csiro.au/wf/WF21124}, author = {Jasmine Innocent and Duncan Sutherland and Nazmul Khan and Khalid Moinuddin} } @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-8374, title = {Firebrand transport from a novel firebrand generator: numerical simulation of laboratory experiments}, journal = {International Journal of Wildland Fire}, volume = {31}, year = {2022}, month = {05/2022}, chapter = {634}, abstract = {

Firebrands (often called embers) increase the propagation rate of wildfires and often cause the ignition and destruction of houses. Predicting the motion of firebrands and the ignition of new fires is therefore of significant interest to fire authorities. Numerical models have the potential to accurately predict firebrand transport. The present study focuses on conducting a set of benchmark experiments using a novel firebrand generator, a device that produces controlled and repeatable sets of firebrands, and validating a numerical model for firebrand transport against this set of experiments. The validation is conducted for the transport of non-burning and burning cubiform firebrand particles at two flow speeds. Four generic drag sub-models used to estimate drag coefficients that are suited for a wide variety of firebrand shapes are verified for their applicability to firebrand transport modelling. The four sub-models are found to be good in various degrees at predicting the transport of firebrand particles.

}, keywords = {contour, contour peak location, drag models, embers, fire dynamics simulator, firebrand generator, Lagrangian particles, lateral spread, short-range firebrands}, doi = {https://doi.org/10.1071/WF21088}, url = {https://www.publish.csiro.au/wf/Fulltext/WF21088}, author = {Rahul Wadhwani and Duncan Sutherland and A Ooi and Khalid Moinuddin} } @conference {bnh-8333, title = {Improvement of drag model for non-burning firebrand transport in Fire Dynamics Simulator }, booktitle = {24th International Congress on Modelling and Simulation}, year = {2021}, month = {12/2021}, address = {Sydney, NSW}, abstract = {

Firebrands play a crucial role in increasing the severity of wildfires by driving fire growth, damaging structures, and starting new fires. Predicting the transport of firebrands and their propensity to ignite new fires is of significant interest to fire communities. Developing an operational firebrand transport sub-model from the field studies is cumbersome, expensive, and has significant associated risks to equipment, community and firefighters. Physics-based models have the potential to assist in the development of such firebrand transport sub-models which can be utilised to improve the efficacy of existing operational fire models. The present study showcases one of the initial works carried out in the development of such a physics-based firebrand model. The work utilises Fire Dynamics Simulator (FDS), a commonly used open-source physicsbased fire model. The Lagrangian particle sub-model of FDS is used to simulate the transport of firebrand particles. The Lagrangian sub-model is generally used to model the transport of droplets and mist and has been extensively validated. However, the validation of this sub-model for the transport of solid particles such as firebrands is limited. The issue is exacerbated when particles are of a non-spherical shape and can undergo complex reactions over their transport such as burning. In this work, we utilise a firebrand generator prototype that produces a uniform Lagrangian shower of nonburning idealised firebrands. A set of in-house experiments are conducted to study the transport of three isometric shapes of non-burning firebrands i.e. cubiform, cylindrical and square-disc. These sets of experiments are used to quantify the efficacy of the inbuilt particle drag model of FDS and suggest potential alternative drag models that can be employed without loss of computational speed, major amendment in the fire model, are applicable to a wide range of particles shapes, and potentially improved prediction. In general, it is found that the suggested alternative Haider and Levenspiel drag model improves the estimation of firebrand distribution in terms of peak location, maximum and minimum longitudinal distribution with exception to cubiform particles for peak location. The exception is mainly due to inherent error association with the alternative drag model in overestimating the drag coefficient. For other situations, Haider and Levenspiel drag model shows either an improvement or stays the same. However, the study found that the existing point particle assumption to represent particles in FDS is not suited to estimate the lateral spread of firebrands especially when the secondary motion of a particle on its axis is involved such as cylindrical and square-disc particles. Our studies found, the lateral spread is found to be in the range of ~5-15\% thinner compared to its experimental width for cylindrical particle distribution. For the square disc, it is not possible to quantify such differences due to the computational limit associated with our present study. It can be qualitatively suggested that it is found to be more than cylindrical particles. A further set of experiments and their numerical validation is required to ascertain the above finding, especially with different sizes, isometric and non-isometric shape, the speed of firebrand particles and burning process to establish the efficacy of a particular drag model for firebrand transport.

}, keywords = {drag models, Fire Dynamics Simulator (FDS), firebrand generator, firebrand particles, Lagrangian particle}, url = {https://www.researchgate.net/profile/Rahul-Wadhwani/publication/356914453_Improvement_of_drag_model_for_non-burning_firebrand_transport_in_Fire_Dynamics_Simulator/links/61c2c9e28bb20101842b52be/Improvement-of-drag-model-for-non-burning-firebrand-transport}, author = {Rahul Wadhwani and Duncan Sutherland and Graham Thorpe and Khalid Moinuddin} } @article {bnh-8157, title = {Numerical study on effect of relative humidity (and fuel moisture) on modes of grassfire propagation}, journal = {Fire Safety Journal}, year = {2021}, month = {08/2021}, abstract = {

Relative humidity of air is directly related to fuel moisture. Fuel moisture is often considered as the index of flammability in the context of bushfire. Variation of relative humidity and fuel moisture is considered to have a significant effect on the rate of spread of grassfire propagation and fire intensity. In this study, four sets of grassfire simulations have been conducted: three sets with 210 mm high grass and another set with 175 mm high grass. For all sets, the ambient temperature was kept constant while relative humidity and fuel moisture were varied, with fuel moisture deduced from the McArthur MKV GFDI model. With 210 mm grass heights, driving wind velocities were varied. Lower relative humidity (and fuel moisture) was observed to lead to higher fire intensity and a faster rate of spread, which are intuitively expected. Byram number analysis showed that relative humidity (and fuel moisture) can lead to change in the fire propagation mode (wind-driven vs buoyancy-driven), but the greater factor is the wind velocity.

}, keywords = {Byram number, grassfire, Mode of fire propagation, Physics-based modelling, relative humidity}, doi = {https://doi.org/10.1016/j.firesaf.2021.103422}, url = {https://www.sciencedirect.com/science/article/abs/pii/S0379711221001636}, author = {Khalid Moinuddin and Nazmul Khan and Duncan Sutherland} } @article {bnh-7838, title = {A response to comments of Cruz et al. on: {\textquoteleft}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{\textquoteright}}, journal = {International Journal of Wildland Fire}, year = {2021}, month = {02/2021}, abstract = {

In response to Cruzet al.(2020b) (hereafter: CSG20), we would like to clarify that we are committed to further research into the mechanisms that drive fire spread in grassland fuels, and are open to making the most of synergies that exist between various programs of research. As demonstrated by Filippiet al.(2013), Kochanskiet al.(2013), Clementset al.(2019), etc., there is much to be gained by combining detailed experimental data with rigorous computational modelling.

}, keywords = {Byram number, fuel height, grass fire, modes of fire propagation, rate of spread.}, doi = {https://doi.org/10.1071/WF20091}, url = {https://www.publish.csiro.au/WF/WF20091}, author = {Duncan Sutherland and Jason J. Sharples and William Mell and Khalid Moinuddin} } @article {bnh-6822, title = {Effect of relative humidity on grassfire propagation}, number = {561}, year = {2020}, month = {04/2020}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

The relative humidity of air is directly related to fuel moisture. Fuel moisture is often considered as the index of flammability in the context of bushfires. Variation of relative humidity and fuel moisture is considered to have a significant effect on the rate of spread of grassfire propagation and fire intensity. In this study, two sets of grassfire simulations have been conducted: one set with 0.21m grass and another set with 0.175m grass. For both sets the ambient temperature was kept constant while the relative humidity and fuel moisture were varied, with fuel moisture deduced from the McArthur MKIII-V GFDI model. A lower relative humidity was observed to lead to higher fire intensity and a faster rate of spread, which are intuitively expected. Froude number analysis showed that relative humidity can lead to change in the fire propagation mode (wind driven vs buoyancy driven), but the greater factor appears to be grass height (fuel load).

}, keywords = {grassfire, modelling, propagation, relative humidity}, issn = {561}, author = {Khalid Moinuddin and Tehmina Khan and Duncan Sutherland} } @article {bnh-6900, title = {Fire spread prediction across fuel types: annual report 2018-19}, number = {564}, year = {2020}, month = {05/2020}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

The prediction of the rate of spread and intensity of bushfires is crucial for emergency and disaster management organisations for operational planning and the deployment of resources.\  Currently, simplified operational models are used since the prediction can be obtained on time scales commensurate with those required by emergency managers. Our aim is to refine these non-physics-based operational tools so that they can predict fire behaviour under a wide range of localised topographic and weather conditions, and also that they are able to account for a range of inhomogeneity, slope, and thermal instability within vegetation and over the terrain. Furthermore, a more physically-motivated firebrand model needs to be included in operational models to predict firebrand landing and the increased rate of fire spread (RoS).

In the last few years, we have numerically tested and established a reliable physics-based model that is based on basic fire dynamics theory and corresponding differential equations to simulate bushfire scenarios. We now embark upon utilization of our research as well as extending parametric study using the physics-based model. The following aspects have been the highlights of our endeavour:

Overall we have achieved our goal to obtain greater insight into bushfire physics and we are now utilising these insights to parameterise various phenomenon for operational models.

}, keywords = {fire spread, fuel types, prediction}, issn = {564}, author = {Mahmood Rashid and Duncan Sutherland and Khalid Moinuddin} } @article {bnh-7359, title = {Physics-Based Simulations of Flow and Fire Development Downstream of a Canopy}, journal = {Atmosphere}, volume = {11}, year = {2020}, month = {06/2020}, abstract = {

The behavior of a grassland fire propagating downstream of a forest canopy has been simulated numerically using the fully physics-based wildfire model FIRESTAR3D. This configuration reproduces quite accurately the situation encountered when a wildfire spreads from a forest to an open grassland, as can be the case in a fuel break or a clearing, or during a prescribed burning operation. One of the objectives of this study was to evaluate the impact of the presence of a canopy upstream of a grassfire, especially the modifications of the local wind conditions before and inside a clearing or a fuel break. The knowledge of this kind of information constitutes a major element in improving the safety conditions of forest managers and firefighters in charge of firefighting or prescribed burning operations in such configurations. Another objective was to study the behavior of the fire under realistic turbulent flow conditions, i.e., flow resulting from the interaction between an atmospheric boundary layer (ABL) with a surrounding canopy. Therefore, the study was divided into two phases. The first phase consisted of generating an ABL/canopy turbulent flow above a pine forest (10 m high, 200 m long) using periodic boundary conditions along the streamwise direction. Large Eddy Simulations (LES) were carried out for a sufficiently long time to achieve a quasi-fully developed turbulence. The second phase consisted of simulating the propagation of a surface fire through a grassland, bordered upstream by a forest section (having the same characteristics used for the first step), while imposing the turbulent flow obtained from the first step as a dynamic inlet condition to the domain. The simulations were carried out for a wind speed that ranged between 1 and 12 m/s; these values have allowed the simulations to cover the two regimes of propagation of surfaces fires, namely plume-dominated and wind-driven fires

}, keywords = {canopy, fire spread, grassland fire, Large Eddy Simulation, physics-based model}, doi = {https://doi.org/10.3390/atmos11070683}, url = {https://www.mdpi.com/2073-4433/11/7/683}, author = {Gilbert Accary and Duncan Sutherland and Nicolas Frangieh and Khalid Moinuddin and Ibrahim Shamseddine and Sofiane Merdji and Dominique Morvan} } @article {bnh-6638, title = {Recirculation regions downstream of a canopy on a hill}, number = {538}, year = {2020}, month = {01/2020}, institution = {Bushfire \& Natural Hazards CRC}, address = {Melbourne}, abstract = {

The large eddy simulation (LES) is performed to study the flow characteristics of atmospheric boundary layer over forested hills. The sparse and dense canopies are introduced in the hill structure and modelled by homogenous leaf area density. A pressure driven flow is established under neutrally stratified condition to explore the effect of hill and canopy induced perturbations including velocity speed-up, separation, attachment and recirculation. The presence of recirculation zone in the lee side of the can change the behavior of the flow field significantly. To be specific, the smoke and firebrand transport, spotfire ignition and fire intensity can be influenced by the formation of recirculation zone in the lee side forested hill. Moreover, the flow separation and attachment in the lee side of the hill or in near forest clearing can change the fire behavior and rate of spread significantly. This study extends previously developed physics-based simulations for the flow through forest canopies over flat surfaces by Duncan et al. [1] with inclusion of hilly terrains. The motivation is to develop a predictive model for the firebrand transport and spotfire ignition model extending the previous work of Rahul et al. [2], where a physics based firebrand model is developed and validated against laboratory-scale experimental data. How the recirculation can affect the formation and growth of firebrand transport and spotfire ignition in the hilly terrain is the long-term goal of this study. The streamwise mean velocity is increases with increases of hill height and canopy densities over a forested hill. The flow recirculation zone is nicely captured on the lee side of the hill with various degrees of size and shape with respect to vegetation densities and hill sizes. The size and shape of the recirculation zones largely depend on the steepness of the hill although canopy density has some contribution as well. The results of streamwise mean velocities, mean pressure, Reynolds stresses and streamlines of velocity fields are captured in this study, which are qualitatively in good agreement with the existing literature. Overall the simulation results show the applicability of FDS in such complex simulation that can be used in future studies for the fire simulation of hilly terrain.

}, keywords = {canopy, downstream, fire simulation, hilly terrain, recirculation}, issn = {538}, author = {Nazmul Khan and Duncan Sutherland and Khalid Moinuddin} } @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-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-7242, title = {The effect of ignition protocol on grassfire development}, journal = {International Journal of Wildland Fire}, volume = {29}, year = {2019}, month = {11/2019}, pages = {70-80}, abstract = {

The effect of ignition protocol on the development of grassfires is investigated using physics-based simulation. Simulation allows measurement of the forward rate of spread of a fire as a function of time at high temporal resolution. Two ignition protocols are considered: the inward ignition protocol, where the ignition proceeds in a straight line from the edges of the burnable fire plot to the centre of the plot; and the outwards ignition protocol, where the ignition proceeds from the centre of the burnable fire plot to the edges of the plot. In addition to the two ignition protocols, the wind speed, time taken for the ignition to be completed and ignition line length are varied. The rate of spread (R) of the resultant fires is analysed. The outwards ignition protocol leads to an (approximately) monotonic increase in\ R, whereas the inward ignition protocol can lead to a peak in\ R\ before decreasing to the quasi-equilibrium\ R. The fires simulated here typically take 50 m from the ignition line to develop a quasi-equilibrium\ R. The results suggest that a faster ignition is preferable to achieve a quasi-equilibrium\ R\ in the shortest distance from the ignition line.

}, keywords = {grassfire, ignition, physics simulation}, doi = {https://doi.org/10.1071/WF19046}, url = {https://www.publish.csiro.au/WF/WF19046}, author = {Duncan Sutherland and Jason J. Sharples 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} } @article {bnh-5675, title = {Physics-Based Simulation of Heat Load on Structures for Improving Construction Standards for Bushfire Prone Areas}, journal = {Frontiers in Mechanical Engineering}, volume = {5}, year = {2019}, month = {06/2019}, abstract = {

Australian building standard AS 3959 provides mandatory requirements for the construction of buildings in bushfire prone areas in order to improve the resilience of the building to radiant heat, flame contact, burning embers, and a combination of these three bushfire attack forms. The construction requirements are standardized based on the bushfire attack level (BAL). BAL is based on empirical models which account for radiation heat load on structure. The prediction of the heat load on structure is a challenging task due to many influencing factors: weather conditions, moisture content, vegetation types, and fuel loads. Moreover, the fire characteristics change dramatically with wind velocity leading to buoyancy or wind dominated fires that have different dominant heat transfer processes driving the propagation of the fire. The AS 3959 standard is developed with respect to a quasi-steady state model for bushfire propagation assuming a long straight line fire. The fundamental assumptions of the standard are not always valid in a bushfire propagation. In this study, physics based large-eddy simulations were conducted to estimate the heat load on a model structure. The simulation results are compared to the AS 3959 model; there is agreement between the model and the simulation, however, due to computational restrictions the simulations were conducted in a much narrower domain. Further simulations were conducted where wind velocity, fuel load, and relative humidity are varied independently and the simulated radiant heat flux upon the structure was found to be significantly greater than predicted by the AS 3959 model. The effect of the mode of fire propagation, either buoyancy-driven or wind dominated fires, is also investigated. For buoyancy dominated fires the radiation heat load on the structure is enhanced compared to the wind dominated fires. Finally, the potential of using physics based simulation to evaluate individual designs is discussed.

}, keywords = {building standards, emissions, forest fire, physics-based simulation, wildland fire, wildfire, fire spread}, doi = { https://doi.org/10.3389/fmech.2019.00035}, url = {https://www.frontiersin.org/articles/10.3389/fmech.2019.00035/full}, author = {Nazmul Khan and Duncan Sutherland and Rahul Wadhwani and Khalid Moinuddin} } @article {bnh-5477, title = {A preliminary report on simulation of flows through canopies with varying atmospheric stability}, number = {469}, year = {2019}, month = {03/2019}, institution = {Bushfire and Natural hazards CRC}, address = {Melbourne}, abstract = {

Large eddy simulation is performed for a flow through forest canopy applying various atmospheric stability conditions. The canopy is modelled as a horizontally homogenous region of aerodynamic drag with a leaf-area density (LAD) profile approximating the profile of a Scots pine tree. Varying atmospheric stability is incorporated into the simulation by applying varying heat flux in two different ways; (i) a surface heat flux prescription using Monin-Obukhov similarity functions and, (ii) a canopy heat flux model where heat from the canopy is modelled as distributed volume heat source. When the surface heat flux was prescribed, five stability classes: very unstable, unstable, neutral, stable and very stable are modelled while for canopy heat flux model three classes: stable, unstable and neutral are simulated for this study. We observe, realistically, that the stable and very stable velocity profiles are leaned towards right to neutral velocity profile indicating wind dominated flow. On the other hand, unstable and very unstable velocity profiles become more vertical indicating buoyancy dominated flow. In all velocity profiles, an inflection point is observed in the dense canopy region. Expected variations in the temperature profiles are also observed {\textendash} higher near-ground temperature for unstable and very unstable cases and converse is true for stable and very stable cases. Simulations involving exponential heat source variation vertically for forest canopy is ongoing for validation with experimental data and other similar studies. Once validation is obtained, parametric study with various atmospheric stability can be carried out in order to improve operational models. \ 

}, keywords = {atmospheric surface layer, forest canopy, thermal stratification, turbulence, turbulent kinetic energy}, author = {Nazmul Khan and Duncan Sutherland and Jimmy Philip and Andrew Ooi and Khalid Moinuddin} } @conference {bnh-5504, title = {Simulated transport of short-range embers in an idealised bushfire}, booktitle = {6th International Fire Behavior and Fuels Conference}, year = {2019}, month = {04/2019}, abstract = {

Mega-bushfires like the 2009 Black Saturday, Australia, the 2016 Fort McMurray fire, Canada, and the 2018 Carr fire, USA cause billions of dollars in damage and result in loss of life. The sources of ignition of the fires are often natural or accidental such as lightning, campfire, cigarette butts, or machinery and tools (Miller, Plucinski et al. 2017). The frequency of bushfires isset to increase due to the positive feedback effect of climate change (Jolly, Cochrane et al. 2015). There is an increasing trend of settlement of people at wildland-urban-interface (WUI) (Radeloff, Helmers et al. 2018) which increases the impact of bushfire. Accurate and quick prediction of the evacuation of communities and the behaviour of a bushfire will make a difference in reducing the impact of bushfire (Mell, McDermott et al. 2010, Ronchi, Gwynne et al. 2017).

}, keywords = {bushfire management, fire behavour. fire impacts, modeling}, url = {https://www.researchgate.net/publication/332142658_Simulated_transport_of_short-range_embers_in_an_idealised_bushfire}, author = {Rahul Wadhwani and Khalid Moinuddin and Duncan Sutherland} } @conference {bnh-6406, title = {Simulations of radiation heat flux on a structure from a fire in an idealised shrubland }, booktitle = {Bushfire and Natural Hazards CRC Research Day AFAC19}, year = {2019}, month = {12/2019}, address = {Melbourne}, abstract = {

Wildland-urban interface areas are growing rapidly. Building standards are required to ensure that the structures built in fire prone areas are resilient to fire. Australian Standard AS 3959 was developed to prescribe construction requirements for houses in bushfire prone areas. The model in AS 3959 is applied to estimate the Bushfire Attack Level (BAL) that is expected on a structure during the nominally worst-case bushfire scenario that the house can experience. Once the BAL is based on the fuel and terrain near the structure, and determines the construction requirements for the structure. AS 3959 is based upon a view-factor model of radiant heat flux, which estimates the level of heat flux expected at the structure.

}, keywords = {building standards, Fire, heat flux, structure, Wildland-urban interface}, url = {https://knowledge.aidr.org.au/resources/australian-journal-of-emergency-management-monograph-series/}, author = {Khalid Moinuddin and Duncan Sutherland} } @article {bnh-4976, title = {Improvements to wind field generation in physics-based models to reduce spin-up time and to account for terrain, heated earth surface}, year = {2018}, month = {10/2018}, institution = {Bushfire and Natural Hazards CRC}, abstract = {

Wind is one of the most important environmental variables that affects the wildland fire spread and intensity. Previously, fire analysts and managers have relied on local measurements and site-specific forecasts to determine winds influencing a fire. However, advances in computer hardware increased the availability of electronic topographical data, and advances in numerical methods for computing winds have led to the development of new tools capable of simulating wind flow. Several numerical models have been developed for fire prediction. The most widely used physics-based models come with a limitation of computational expenses, because of which these are not suitable for operational use. Our main intention of this study is to reduce this limitation of physics-based models so that fire forecasts can be made faster and easier. Modelling wind in physics-based models such as Fire Dynamics Simulator (FDS) has been shown to reproduce promising results, but at an inordinate cost. So, we will be using FDS as physics-based model to simulate fire. There are various methods available to generate wind field in FDS. The conventional methods of wind field generation are either an unperturbed inlet profile with a roughness-trip or the by embedding artificial turbulence at the inlet. The wind fields generated by these inlet conditions are compared with each other as well as to the wind field generated using a mean-forcing method for neutral atmospheric conditions. We have then used these inlet conditions to study the effects of fire spread in FDS. Currently, we are working on introducing a method in FDS known as penalization method, so that we can use real time wind data from other wind models, such as Windninja into FDS and perform fire simulations. Our hypothesis is that introduction of this method would reduce the simulation time of fire cases to some extent and moreover can include terrain effect in the wind profiles.

}, issn = {415}, author = {Khalid Moinuddin and Sesa Singha Roy and Duncan Sutherland and Nazmul Khan} } @article {bnh-5197, title = {Literature review: modelling and simulation of flow over tree canopies}, year = {2018}, month = {12/2018}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

We review recent literature on the topic of atmospheric boundary-layer flow over forest canopies. Included in this review are brief discussions of flow over rough surfaces and flow over urban canopies (collections of buildings). The purpose of this review is to inform fire behaviour analysts of progress in sub-canopy modelling, with an eye to developing simplified models for wind reduction factors. The wind reduction factor is a parameter that quantified the effect of canopy density on fire spread rate. Simulation of canopy flow is also reviewed and discussed. Simulations provide insight into the flow behavior that is otherwise difficult to obtain from field observations and experiments. The basic principles of Large Eddy Simulation and the validity of the simulation results are discussed. Finally some open problems are posed.

}, issn = {432}, author = {Duncan Sutherland and Jimmy Philip and Andrew Ooi 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} } @conference {bnh-5023, title = {Simulations of the effect of canopy density profile on sub-canopy wind speed profiles}, booktitle = {AFAC18}, year = {2018}, month = {09/2018}, publisher = {Bushfire and Natural Hazards CRC}, organization = {Bushfire and Natural Hazards CRC}, address = {Perth}, author = {Duncan Sutherland and Rahul Wadhwani and Jimmy Philip and Andrew Ooi and Khalid Moinuddin} } @article {bnh-5212, title = {Simulations of the effect of canopy density profile on sub-canopy wind speed profiles}, year = {2018}, month = {12/2018}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

In computational simulations for weather prediction and fire simulation, forest canopies are often modelled as regions of aerodynamic drag. The magnitude of the drag term depends on the Leaf-Area Density (LAD) of the forest. For most forests LAD varies strongly with height; trees typically have more vegetation at the top of the canopy than the bottom. S. Dupont, and Y. Brunet [Influence of foliar density profile on canopy flow: a large-eddy simulation study. Agricultural and forest meteorology, 148(6), pp.976-990. 2008] simulated the flow through three very different profiles of LAD measured from three different Canadian forests.\  K. Moon, T.J. Duff, and K.G. Tolhurst [Sub-canopy forest winds: understanding wind profiles for fire behaviour simulation, Fire Safety Journal, 2016] recently measured the sub-canopy winds and LAD for seven different Australian forest types. Large-Eddy Simulations (LES) of flow through idealised forests are now computationally tractable and an extensive systematic study of different LAD profiles is possible. Here we assume that the LAD can be modelled by a Gaussian with two parameters representing the mean and variance of the distribution of LAD. The total vegetation density is forced to remain constant as the profile changes. We present preliminary simulation results showing how the mean and variance of LAD affects the sub-canopy wind velocity and we discuss a potential modelling approach for sub-canopy wind velocity.

}, issn = {442}, author = {Duncan Sutherland and Rahul Wadhwani and Jimmy Philip and Andrew Ooi and Khalid Moinuddin} } @article {bnh-3918, title = {Kinetics of pyrolysis of litter materials from pine and eucalyptus forests}, journal = {Journal of Thermal Analysis and Calorimetry}, year = {2017}, month = {06/2017}, abstract = {

Wildfires are an integral feature of the Australian continent. To estimate the rate of spread of wildfires using computational models it is important to know the kinetic parameters of the materials that constitute the fuel load in forests. These kinetic parameters are utilised in pyrolysis and combustion sub-models of a computational model. In the present work, the kinetics of pyrolysis of timber and litter materials (consisting of bark, twigs, and leaves) from\ Pinus radiata\ and\ Eucalyptus obliqua\ subsp.\ messmate\ forests were estimated under nitrogen. The activation energy for the pyrolysis of timber was found to be independent of conversion, whereas it varied for the litter materials in the range of the pyrolysis temperatures employed. Furthermore, the parameters pertaining to a single equivalent reaction model were also identified. For the samples studied, the most suitable reaction model was identified as the Johnson{\textendash}Mehl{\textendash}Avrami model. The activation energy measurements reported here are consistent with measurements previously reported for other species within the\ Pinus\ and\ Eucalyptus\ genera.

}, doi = {10.1007/s10973-017-6512-0}, url = {https://link.springer.com/article/10.1007/s10973-017-6512-0}, author = {Rahul Wadhwani and Duncan Sutherland and Khalid Moinuddin and Paul Joseph} } @conference {bnh-3882, title = {Large-eddy simulation of neutral atmospheric surface layer flow over heterogeneous tree canopies}, booktitle = {AFAC17}, year = {2017}, month = {09/2017}, publisher = {Bushfire and Natural Hazards CRC}, organization = {Bushfire and Natural Hazards CRC}, address = {Sydney}, abstract = {

Large-eddy simulation of a neutral atmospheric surface layer (ASL) flow is per- formed over a modelled tree canopy with heterogeneous leaf-area density. The canopy is arranged as a series of equally-sized stripes of different leaf-area density, emulating the study of Bou-Zeid et al. (E. Bou-Zeid, C. Meneveau, and M.B. Parlange. Large-eddy simulation of neutral atmospheric boundary layer flow over heterogeneous surfaces: Blending height and effective surface roughness. Water Resources Research, 40(2), 2004.) over heterogeneous rough surfaces. The simulation results are analysed to understand the qualitative similarities and differences between ASL flows over heterogeneous canopies and heterogeneous roughnesses. This will allow, in the future, the identification of the equivalent roughness length, displacement length, and blending height which parameterises the flow above the heterogeneous canopy. In the present work we restrict attention to the characterisation of the four canopy case and the blending height and β parameter, the ratio of shear stress to velocity at the canopy top. The general characteristics of the four-canopy case are representative of the other cases. Strong vertical velocities (ie up- and down-drafts) exist at the interface between the heterogeneous roughness stripes. However, for a canopy, vertical velocity couplets exist on the vertical interface between two canopies. This implies the presence of sub-canopy recirculation zones at canopy interfaces, which can be confirmed by visualisation of the fluid streamlines. Above the canopy internal boundary layers form over each canopy stripe and exhibit similar features to the characteristic upstream plumes of flow over a rough surface. The shear stress immediately above the canopy varies over the stripes but it varies more smoothly over a canopy than over a heterogeneous roughness. These simulations will allow the development of parameterisations for the near-surface layer and the sub-canopy winds. A better understanding of the effect of heterogeneous canopies on the sub-canopy winds will improve predictions of the wind reduction factor, and in turn, improve operational fire spread predictions.

}, author = {Duncan Sutherland and Khalid Moinuddin and Andrew Ooi} } @article {bnh-4229, title = {Numerical modelling of fires on forest floor and canopy fires}, number = {352}, year = {2017}, month = {11/2017}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

The Wildland Urban Interface Fire Dynamics Simulator (WFDS) is a physics-based fire model developed by the US Forest Department and to simulate fire spread in landscapes. It is an extension of National Institute of Standards and Technology (NIST) building fire model Fire Dynamics Simulator (FDS). Currently both models have the capability to model surface fire as well as crown fire. Both quantitative and qualitative analyses are important for further advancement. This study shows that for quantitative analysis, grid convergence is not elusive and the grid converged solution agrees well with the experimental result involving ignition of a Douglas fir tree. The WFDS model is also capable of qualitatively predicting propagation of surface fire to the forest canopy.

}, issn = {352}, author = {Khalid Moinuddin and Duncan Sutherland} } @conference {bnh-4075, title = {Suitable pyrolysis model for physics-based bushfire simulation}, booktitle = {11th Asia-Pacific Conference on Combustion}, year = {2017}, month = {12/2017}, publisher = {The Combustion Institute}, organization = {The Combustion Institute}, address = {Sydney}, abstract = {

Models for the thermal degradation (or pyrolysis) of solid fuel are fundamental to the physics-based simulation of grassfires. The pyrolysis process affects the combustion process and therefore the simulated flame, which defines the fire front. There are two competing models: a simple linear parameterisation and a non-linear Arrhenius model. The present work appraises these two models for Lucerne hay (a cured herbaceous fuel) to test their suitability for bushfire simulation. Thermogravimetric analysis and differential scanning
calorimetry of Lucerne hay is conducted to measure the parameters required for the simulation. Simulations of pyrolysis are carried out using both the linear and single effective Arrhenius models, and compared with the
experimental results. For this fuel, the linear model provides better agreement with the experimental data than the Arrhenius model. Hence, the linear model would be more suitable for large-scale wildfire simulation.

}, author = {Rahul Wadhwani and Duncan Sutherland and Khalid Moinuddin} } @article {bnh-3917, title = {Verification of a Lagrangian particle model for short-range firebrand transport}, journal = {Fire Safety Journal}, volume = {91}, year = {2017}, month = {07/2017}, pages = {776-783}, chapter = {776}, abstract = {

Firebrands are a harbinger of damage to infrastructure; their effects cause a particularly important threat to people living within the wildland-urban-interface. Short-range firebrands travel with the wind with little or no lofting, and cause spotfires. In this work, the design of a novel firebrand generator prototype is discussed to achieve a uniform shower of firebrands. The transport of short-range firebrand is studied to verify the existing Lagrangian particle model of Fire Dynamics Simulator. Uniform, non-combusting cubiform and cylindrical firebrands are projected using the firebrand generator. The experimentally observed distribution of particles on the ground is compared with a simulated distribution using the fire dynamic simulator. The results show that the existing Lagrangian model gives a good agreement with the experimental data.

}, doi = {10.1016/j.firesaf.2017.03.019}, url = {http://www.sciencedirect.com/science/article/pii/S0379711217301121}, author = {Rahul Wadhwani and Duncan Sutherland and Andrew Ooi and Khalid Moinuddin and Graham Thorpe} } @article {bnh-3049, title = {Fire spread prediction across fuel types: Annual project report 2015-2016}, number = {214}, year = {2016}, month = {09/2016}, institution = {Bushfire and Natural Hazards CRC}, address = {Melbourne}, abstract = {

Operational models that are used to predict fire behaviour can be implemented easily and rapidly. However, the operational models are only truly valid in the range of experimental conditions used to build the model. This leads to a number of difficulties when using the existing operational models to predict real-world wildfires. Physics-based modelling, that is simulating the fire behaviour from the basic equations of atmospheric fluid flow, combustion, and thermal degradation of fuel materials offers considerable insight into the dynamics of wildfire. However, physics-based simulations are computationally intensive and, at present, can only be applied to small, idealised cases. Nevertheless, the aim of this project is to use physics based models to gain insight into wildfire behaviour and use that insight to improve the current operational models for fire behaviour prediction. With this in mind, a number of investigations are underway.

The effect of a tree canopy on the near surface wind speed is investigated using Large Eddy Simulation with a view to modelling the wind reduction factor due to the canopy. The wind reduction factor is used in operational fire prediction models such as the McArthur model, to account for the reduction in wind velocity due to a tree canopy. A set of full three-dimensional simulations over idealised rectangular canopies, where the length and leaf area density of the canopy are varied, were conducted. The flow over the canopy is characterised and the potential effects on fire spread of complicated flow structures that develop at the leading and trailing edges are assessed. The simulated wind speed in the fully-developed canopy flow and the wind speed far from canopy region is used to assess the constant wind-reduction factor modelling approach.

The physics of firebrand, or ember, transport is not well understood. The distance and dispersion of the firebrands depends greatly on the turbulent fluid flow which transports the firebrands. The physics-based modelling of firebrand transport is at a preliminary stage. We seek to validate a Lagrangian particle approach for firebrand transport modelling by comparing the results from an experimental firebrand generator with simulations of same scenario. Three particle shapes, cubical, cylindrical, and disc shaped particles, representing idealised firebrands have been studied. Qualitative features of the landing distribution of the firebrands have been identified. Simulations are in progress to compare with the experimental results. So far the results are encouraging. In a related study, the thermos-kinetic properties of firebrand materials, such as bark, twigs, and leaves have been measured. This data will then be used for simulations of burning firebrands.\ 

Fires in grasslands are prevalent in Australia, and are relatively simple to model computationally due to the uniform fuel and flat simple terrain. In the present study, the CSIRO grassland experiments are used as validation cases for the physics-based simulations.\  A parametric study has been conducted where the background windspeed and the grass height have been varied independently.\  The rate-of-spread was found to be linear with windspeed in the parameter range considered. Two simulations were conducted at different heights and correspondingly different bulk density, representing grass which had been cut and left on the ground.\  The fire in the taller grassland was found to have a higher rate-of-spread. Three simulations were conducted where the bulk density was kept constant as height varied. In these simulations no systematic dependence on grass height was observed.

Direct Numerical Simulation (DNS) is a numerical technique to faithfully study fluid flows by resolving all the turbulent motions instead of resorting to modelling small scale turbulence. DNS provides great insight into the physics of flows but a limited to highly idealised and numerically tractable geometries such as channels. Nonetheless, such simulations can be used to gain insight into flows which have relevance to wildfire modelling. Three flows are studied: pressure driven flow over sinusoidal roughness, mixed convective flow (flow driven by both a temperature difference and a pressure gradient), and a buoyant line plume in a confined region.

In the future, the DNS work will contribute to improved turbulence and near-wall modelling used in the physics-based wildfire models. The results of simulations from physics-based wildfire models will in turn improve operational models. We eventually aim to produce models for the wind-reduction factor, improve knowledge of firespread in grasslands, and provide a model of firebrand transport, all of which can be used operationally.\ 

}, author = {Khalid Moinuddin and Duncan Sutherland and Graham Thorpe} } @article {bnh-2393, title = {The spread of fires in landscapes}, year = {2015}, author = {Daniel Chung and Khalid Moinuddin and Andrew Ooi and Duncan Sutherland and Graham Thorpe and Rahul Wadhwani} }