@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-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-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-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} }