Wind behaviour in junction fires
Résumé
Extreme fire behavior has a great impact on communities and the environment, posing a significant threat to public safety and causing billions of dollars in damage. Their frequency has increased globally in recent years and is expected to keep increasing due to climate change. One type of these extreme behaviors is known as junction fires. Junction fires involve the merging of two fire fronts and have the potential to exhibit a rapid increase in rate of spread and fire intensity over a short period of time. While there are several studies simulating this phenomenon in a variety of scales there is a lack of experimental results to verify the models and further understand the interactions between local weather, fuel and fire. This study presents experimental results obtained during a prescribed fire in Little desert, Victoria. The prescribed burning was conducted by DEECA on April the 26th 2024. 5 plots were burned with two merging fire lines each. The plots had an average dimension of 50m in length and 50m in width. The terrain was locally flat and covered with shrubs up to around 1m in height. This research presents local point measurements of the fire dynamics in the field scale. Different types of instrumentation were used: 4 anemometers, 8 fire packages and an automatic weather station. The fire packages are custom built devices used to measure 3D wind components, temperature and heat flux at a 1Hz frequency. The fire packages were placed within the burning plot with the objective of measuring different spatial components of the fire behavior. To account for vertical variations in temperature and fire wind, the fire packages were placed at two different heights: 20cm and 1.5m above the ground. This allowed to measure flame temperature at two heights and to account for intermittent flaming. The 4 anemometers were placed in the corners of the square delimiting the burning plot to capture inflow and outflows related to the fire. This configuration allowed to measure 2D winds and temperatures at 0.5Hz. The weather station measured ambient conditions at 1Hz: 3D wind, temperature, humidity and solar radiation. Fire progression isochrones will also be used to couple fire progression with airflow dynamics. The flaming stage is marked by a fast rise in temperature as expected. Temperatures then remain over 40°C for around 10 minutes showing little fluctuations. Slight temperature increase was also captured by the anemometers. Wind was locally affected by the fire and the preliminary analysis has shown a strong change in wind direction measured by the anemometers after the ignition and for several minutes after extinction. Current analysis is focused on 3D wind analysis. Having a 1Hz frequency allows for a more complex analysis of the wind temporal behavior and a spatial and temporal characterization of the turbulent structures that could be originated by the fire front. The results derived from this study will be valuable for understanding the influence of convective structures on fire development and progression, as well as for model validation.
| Origine | Fichiers produits par l'(les) auteur(s) |
|---|---|
| Licence |