Published works

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.