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This paper reports two experimental fires conducted at field-scale in Corsica, across a particular mountain shrubland. The orientation of the experimental plots was chosen in such a way that the wind was aligned along the main slope direction in order to obtain a high intensity fire. The first objective was to study the high intensity fire behavior by evaluating the propagation conditions related to its speed and intensity, as well as the geometry of the fire front and its impact on different targets. Therefore, an experimental protocol was designed to determine the properties of the fire spread using UAV cameras and its impact using heat flux gauges. Another objective was to study these experiments numerically using a fully physical fire model, namely FireStar3D. Numerical results concerning the fire dynamics, particularly the ROS, were also compared to other predictions of the FireStar2D model. The comparison with experimental measurements showed the robustness of the 3D approach with a maximum difference of 5.2% for the head fire ROS. The fire intensities obtained revealed that these experiments are representative of high intensity fires, which are very difficult to control in the case of real wildfires. Other parameters investigated numerically (flame geometry and heat fluxes) were also in fairly good agreement with the experimental measurements and confirm the capacity of FireStar3D to predict surface fires of high intensity. [ABSTRACT FROM AUTHOR]

Data collection in the field is fundamental in providing relevant information during fire spread across vegetation or in industrial environments. Considering the challenge and costs of obtaining measurements in the presence of a fire at such a large scale, the development of non-intrusive optical methods is a good alternative. As part of an ongoing effort to improve the understanding of wildfire spread and provide useful tools for fire management, an image-based diagnostic system is being developed for the three-dimensional reconstruction of the turbulent flame in the field. The method allows the time-resolved measurement of the geometric flame features (height, surface area and volume). This paper presents the application of two synchronized stereovision systems to static line of fire scenarios. Each stereovision system, with 1 m inter-camera distance, was located at 12 m from the fire and captured complementary images from front and rear views. Dual spectral band (visible-NIR) cameras were used to enhance fire pixel detection. A series of experiments were carried out on 5 m long and 2 m wide beds of excelsior in the open with fuel loads of 2, 4 and 8 kg/m2. The maximum flame heights were in the range of 1.2–2.4 m. Measurement of the heat flux densities was performed at several positions using thermopile-type sensors. Peak heat fluxes of 6.4–15.7 kW/m2 were measured at 3 m from the fire. The thermal radiation impinging ahead of the flame front was characterized according to its geometric properties. The results exhibit not only a linear relationship between the flame volume and radiant heat flux but also high correlations between their temporal fluctuations. The image processing technique enables measurements of flame volume to be a reliable substitute for the usual fire thermal properties. [ABSTRACT FROM AUTHOR]

• Experimental burning of reconstructed rockrose hedges at field scale. • Anemometer measurements to perform a statistical analysis of the wind on site. • Visible flame geometry extracted using image processing analysis from several cameras. • Radiant and total heat fluxes gauge positioned downstream of the fire to quantify the thermal exposure. • Relationship between wind and flame features have been highlighted. • Low frequency flapping motion of the ensemble flame induced by the turbulent structure of the wind have been shown. With climate change, complex fire scenarios at Wildland Urban Interfaces (WUI) have become a growing concern for authorities worldwide. Such scenarios involve unfavorable wind conditions, which greatly increase the fire spread near communities and makes the intervention of firefighters even more complex. To design effective fire safety regulations to protect communities, it is important to have a clear understanding of the role of wind in the burning of vegetation to help identify the vectors of fire spread within the defensible zone. In this context, this paper attempts to relate the properties of the flames generated by the burning of a reconstructed rockrose hedge to the atmospheric wind turbulence using four field-scale experiments. The experimental setup includes 3 visible cameras to record the flame geometry, extracted by post-processing; 3 pairs of radiant and total heat fluxes to record the heat fluxes downstream of the hedge, and an anemometer to measure the wind speed and direction. The results show that the wind at the experimental site is composed of wall-bounded turbulent structures coupled with strong and short intermittent events such as gusts. Regarding the fire, the four replicates show similarities in phase durations and dynamics, but revealed dependencies on Reynolds number and turbulent kinetic energy when averaging over the fully developed flame phase. In addition, a slight flapping motion of the ensemble flame was observed and associated with wave numbers of the order of the turbulent cascade in the kinetic energy power spectra. Finally, the analysis of wind and fire intermittencies revealed that strong and short wind events generate large fluctuations of flame geometry and received heat fluxes that increase with the characteristic time of the event considered. [ABSTRACT FROM AUTHOR]

This paper reported a high intensity experimental fire conducted during a field-scale experiment on a steep sloped terrain (28°) as part of a winter prescribed burns campaign managed by the local firefighter service in the north-western region of Corsica. The rate of spread (ROS) of fire, measured using UAV cameras (thermal and visible), was evaluated at 0.45 m/s. The experiment was numerically reproduced using a completely physical 2D model, namely FireStar2D, and the comparison with the experimental measurements mainly concerned the fire ROS and the heat fluxes received by three distant targets placed at the end of the plot. The results analysis shows that the considered fire has a wind-driven regime of propagation with a fire intensity higher than 7 MW/m. The numerical results are in fairly good agreement with the experimental measurements, within 11% difference for the ROS and 5% for the heat fluxes, validating consequently the relevance of the numerical approach to tackle such high-intensity wildfires. Despite the unfavorable wind and humidity conditions for fire propagation (U = 1.67 m/s and RH = 82%), this experiment confirms that such fire can exhibit a dangerous behavior due to the steep slope of the terrain. [ABSTRACT FROM AUTHOR]