Physics-based simulations of grassfire propagation on sloped terrain at field scale: motivations, model reliability, rate of spread and fire intensity†
Jasmine Innocent A B , Duncan Sutherland B C , Nazmul Khan
A B and Khalid Moinuddin A B *
+ Author Affiliations
- Author Affiliations
A Institute for Sustainable Industries and Liveable Cities, Victoria University, Melbourne, Australia.
B Bushfire and Natural Hazards Cooperative Research Centre (CRC), East Melbourne, Vic. 3002, Australia.
C School of Science, University of New South Wales, Canberra, ACT 2610, Australia.
* Correspondence to: Khalid.Moinuddin@vu.edu.au
International Journal of Wildland Fire 32(4) 496-512 https://doi.org/10.1071/WF21124
Submitted: 3 September 2021 Accepted: 5 December 2022 Published: 20 January 2023
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of IAWF.
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–urban Interface Fire Dynamics Simulator (WFDS), with varying wind speeds (12.5, 6 and 3 m s−1) and slope angles (−30° to +30°). 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–fire intensity relationship (Byram’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.
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