@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} } @article {bnh-8373, title = {A review of firebrand studies on generation and transport}, journal = {Fire Safety Journal}, volume = {134}, year = {2022}, month = {09/2022}, abstract = {

Firebrands play a vital role in the propagation of fire by starting new fires called spotfires, ahead of the fire front during wildfire progression. Firebrands are a harbinger of damage to infrastructure; their effects particularly pose a threat to people living within the wildland-urban-interface, they can hamper the suppression of wildfire and block evacuation routes for communities and emergency services. Short-range firebrands which travel along with the wind, with little or no lofting, are particularly crucial in increasing fire front propagation and damaging structures situated close to the wildland-urban interface. In the Daylesford fire of 1962 in Australia, massive short-range spotting (the process of spot fire ignition and merging of spots caused by firebrands) occurred in the eucalyptus forest and increased the rate of fire spread by roughly three times more than that computed using an operational fire model. Similarly, long-range firebrands can be transported by the fire plume and ambient wind and can ignite new fire up to 30{\textendash}40\ km from the source of fire as observed in the 2009 Black Saturday fire in Australia.

A large amount of experimental research has been conducted to quantify the effects of firebrands, to develop empirical models and to benchmark results for\ Computational Fluid Dynamic\ (CFD) based fire model validations. In recent years, some CFD models have been studied primarily for their validation purposes. These studies have been reviewed here. To perform useful\ parametric studies\ of firebrand transport using CFD models as well as further development of CFD models, more targeted studies need to be conducted.

}, keywords = {firebrand generator, Firebrand spotting, Firebrand transport, wildfires}, doi = {https://doi.org/10.1016/j.firesaf.2022.103674}, url = {https://www.sciencedirect.com/science/article/pii/S0379711222001515}, author = {Rahul Wadhwani and Catherine Sullivan and Amila Wickramasinghe and Matthew Kyng and Nazmul Khan 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} } @mastersthesis {bnh-6632, title = {Physics-based simulation of short-range spotting in wildfires}, year = {2020}, month = {01/2020}, school = {Victoria University}, address = {Melbourne}, abstract = {

Firebrands play a vital role in the propagation of fire fronts and starting new fires called spotfires ahead of fire fronts during wildfire progression. Firebrands are a harbinger of damage to infrastructure; their effects cause a particularly important threat to people living within the wildland-urban-interface, hampers the suppression of the wildfire or even blocking the evacuation routes for communities and emergency services. Short-range firebrands (\<750m) which travel along with the wind with little or no lofting are particularly crucial in increasing the fire front propagation and damaging structures situated closed to wildland-urban interface. In the Daylesford fire of 1962, massive short-range spotting (the process of spot fire ignition and merging of spots caused by firebrands) occurred in eucalyptus forest and increased the rate of fire spread by roughly three times more than the computed using empiricial correlation used by operational fire model. Despite the massive importance of short-range firebrands, little research has been conducted because of the safety risks and challenges of fire to emergency service personnel and to the remote equipment like collection boxes, IR cameras, UAVs, which could be used by researchers to quantify and measure fire properties. An operational model to represent the transport of short-range firebrand and their likelihood to ignite the surface fuel like forest litter could be developed from a numerical model. This study first attempts to validate a numerical model of firebrand transport with a set of benchmark experiments. The validation of numerical model is carried out using idealised regular shaped firebrand. Fire Dynamic Simulator (FDS) is an open-source Computational Fluid Dynamics (CFD) based fire model which is used in this study. The validation of the numerical model is split into two parts focusing on validation of (1) transport, and (2) ignition potential of firebrands. Transport of short range firebrands are modelled in FDS using a lagrangian particle sub-model. The model was validated using two firebrand generators (a plastic pipe-based prototype and stainless steel based main firebrand generator) constructed at our facility as a part of this study. The firebrand generator is equipment which generates a repeatable firebrand shower in a confined space. There are few firebrand dragons built around the world. However, our firebrand generators produce a uniform flow field which simplifies the transport of short-range firebrand to be validated. The set of experiments conducted is used to validate the Lagrangian particle model available in FDS used in the transport of short-range firebrands. The validation is carried out on cubiform, cylindrical, and square disc-shaped firebrands. As the default drag model in FDS was not suitable for shapes of firebrands, the drag model is improved to account for a generic shape of firebrand particle. The results show a reasonable agreement with the experiments for all three shapes over a range of particle Reynolds number. A set of laboratory scale equipment is used to study the ignition likelihood from a short-range firebrand in the numerical model. The boundary fuel vegetation model of FDS is validated. The pyrolysis of vegetation is first tested using thermogravimetric analyser and then with cone calorimeter to estimate mass loss rate, heat-release rate, and time to sustained flaming ignition of three forest litter (pine, eucalyptus, and hay) fuels. Further, a set of thermo-physical properties (thermal conductivity, heat capacity, the heat of pyrolysis, the heat of combustion) of the material tested are also measured using in-house equipment required in the above numerical model. The result showed that the simple linear pyrolysis model is good enough for different forest litter tested with thermogravimetric analyser and cone calorimeter. Finally, a parametric study of short-range firebrand transport inside an open woodland forest canopy is carried out using the validated Lagrangian particle sub-model. The work focuses on understanding how firebrand distribution varies with a set of variable firebrand characteristics in a wildfire and set a stepping stone for the future study. The results are found to be qualitatively similar to the literature.

}, keywords = {Fire, Firebrands, fluid dynamics, simulation, spotting, transport, Wildfire}, url = {http://vuir.vu.edu.au/40025/}, author = {Rahul Wadhwani} } @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} } @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-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-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-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} }