Simulation study of grass fire using a physics-based model: striving towards numerical rigour and the effect of grass height on the rate of spread

2018 ◽  
Vol 27 (12) ◽  
pp. 800 ◽  
Author(s):  
K. A. M. Moinuddin ◽  
D. Sutherland ◽  
W. Mell
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Heat Release ◽  
Bulk Density ◽  
Simulation Study ◽  
Release Rate ◽  
Rate Of Spread ◽  
Fire Front ◽  
Physics Based Simulation ◽  
Mode A

Grid-independent rate of spread results from a physics-based simulation are presented. Previously, such a numerical benchmark has been elusive owing to computational restrictions. The grid-converged results are used to systematically construct correlations between the rate of spread (RoS) and both wind speed and grass height, separately. The RoS obtained from the physics-based model is found to be linear with wind speed in the parameter range considered. When wind speed is varied, the physics-based model predicts faster RoS than the Mk III and V (McArthur) models (Noble et al. 1980) but slower than the CSIRO model (Cheney et al. 1998). When the grass height is varied keeping the bulk density constant, the fire front changes from a boundary layer flame mode to plume flame mode as the grass height increases. Once the fires are in plume mode, a higher grass height results in a larger heat release rate of the fire but a slower RoS.

scholarly journals The formation of charcoal reflectance and its potential use in post-fire assessments

2016 ◽  
Vol 25 (7) ◽  
pp. 775 ◽  
Author(s):  
Claire M. Belcher ◽  
Victoria A. Hudspith
Keyword(s):  
Heat Release ◽  
Release Rate ◽  
Cone Calorimeter ◽  
Fire Severity ◽  
Combustion Process ◽  
Peak Heat Release Rate ◽  
Fire Front ◽  
Char Oxidation ◽  
Reflectance Microscopy ◽  
Potential Use

Charcoal has an exceptional ability to reflect light when viewed using reflectance microscopy. The amount of light reflected is variable depending on the differential ordering of graphite-like phases within the charcoal itself. It has been suggested that this relates to the temperature of formation, whereby higher formation temperatures result in high charcoal reflectance. However, this explanation is derived from oven-based chars that do not well represent the natural combustion process. Here, we have experimentally created charcoals using a cone calorimeter, in order to explore the development of charcoal reflectance during pre-ignition heating and peak heat-release rate, through to the end of flaming and the transition to char oxidation. We find that maximum charcoal reflectance is reached at the transition between pyrolysis and char oxidation, before its conversion to mineral ash, and indicates that our existing understanding of reflectance is in error. We suggest that charcoal reflectance warrants additional study as it may provide a useful quantitative addition to ground-based fire severity surveys, because it may allow exploration of surface heating after the main fire front has passed and the fire transitions to smouldering phases.

Estimating error in wind speed measurements for experimental fires

2001 ◽  
Vol 31 (3) ◽  
pp. 401-409 ◽  
Author(s):  
A L Sullivan ◽  
I K Knight
Keyword(s):  
Wind Speed ◽  
Small Scale ◽  
Confidence Limits ◽  
Single Measure ◽  
Rate Of Spread ◽  
Scale Size ◽  
Fire Front ◽  
Scalar Measure ◽  
Eucalypt Forests ◽  
Measured Wind Speed

Most experimental fires, by nature, are small scale ([Formula: see text]100 m), and rate of spread measurements are taken over periods of several minutes. The aim of empirical fire modellers is to ascribe a single measure of rate of forward spread over a period to a single scalar measure of wind. The actual wind affecting the fire is unmeasurable; its value must be estimated from remote anemometry. Observation and consideration of the spatial and temporal statistics of the wind has allowed confidence limits to be placed upon the accuracy with which the measured wind reflects the wind acting on the fire front. Experimental data to verify these estimates was gathered during Project Vesta, a study into high-intensity fires in dry eucalypt forests. An equation that quantifies the accuracy of the estimate of wind affecting the fire front is given. The accuracy increases with time scale, size of the fire front, and density of anemometry. When applied to a measured wind speed taken some distance from the fire, it gives a useful estimate of the likely variation of the corresponding wind at the fire front.

scholarly journals The effect of ignition protocol on grassfire development

2020 ◽  
Vol 29 (1) ◽  
pp. 70
Author(s):  
Duncan Sutherland ◽  
Jason J. Sharples ◽  
Khalid A. M. Moinuddin
Keyword(s):  
Wind Speed ◽  
Temporal Resolution ◽  
Line Length ◽  
Forward Rate ◽  
High Temporal Resolution ◽  
Quasi Equilibrium ◽  
Rate Of Spread ◽  
Straight Line ◽  
Shortest Distance ◽  
Physics Based Simulation

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 50m 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.

Corrigendum to: Estimating the amount of water required to extinguish wildfires under different conditions and in various fuel types

2012 ◽  
Vol 21 (6) ◽  
pp. 778
Author(s):  
Rickard Hansen
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Combustion Zone ◽  
Unit Length ◽  
Water Flow Rate ◽  
Flame Length ◽  
Low Intensity ◽  
Surface Fires ◽  
Fire Front

In wildland fires where water is used as the primary extinguishing agent, one of the issues of wildfire suppression is estimating how much water is required to extinguish a certain section of the fire. In order to use easily distinguished and available indicators, the flame length and the area of the active combustion zone were chosen as suitable for the modelling of extinguishing requirements. Using Byram's and Thomas' equations, the heat release rate per unit length of fire front was calculated for low-intensity surface fires, fires with higher wind conditions, fires in steep terrain and high-intensity crown fires. Based on the heat release rate per unit length of fire front, the critical water flow rate was calculated for the various cases. Further, the required amount of water for a specific active combustion zone area was calculated for various fuel models. Finally, the results for low-intensity surface fires were validated against fire experiments. The calculated volumes of water can be used both during the preparatory planning for incidents as well as during firefighting operations.

scholarly journals Estimating the amount of water required to extinguish wildfires under different conditions and in various fuel types

2012 ◽  
Vol 21 (5) ◽  
pp. 525 ◽  
Author(s):  
Rickard Hansen
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Combustion Zone ◽  
Unit Length ◽  
Water Flow Rate ◽  
Flame Length ◽  
Low Intensity ◽  
Surface Fires ◽  
Fire Front

In wildland fires where water is used as the primary extinguishing agent, one of the issues of wildfire suppression is estimating how much water is required to extinguish a certain section of the fire. In order to use easily distinguished and available indicators, the flame length and the area of the active combustion zone were chosen as suitable for the modelling of extinguishing requirements. Using Byram’s and Thomas’ equations, the heat release rate per unit length of fire front was calculated for low-intensity surface fires, fires with higher wind conditions, fires in steep terrain and high-intensity crown fires. Based on the heat release rate per unit length of fire front, the critical water flow rate was calculated for the various cases. Further, the required amount of water for a specific active combustion zone area was calculated for various fuel models. Finally, the results for low-intensity surface fires were validated against fire experiments. The calculated volumes of water can be used both during the preparatory planning for incidents as well as during firefighting operations.

The Speed of a Fire Front and Its Dependence on Wind-Speed

1993 ◽  
Vol 3 (4) ◽  
pp. 193 ◽  
Author(s):  
T Beer
Keyword(s):  
Wind Speed ◽  
Laboratory Tests ◽  
Field Data ◽  
Fire Spread ◽  
Measured Data ◽  
Rate Of Spread ◽  
Wind Rate ◽  
Fire Front ◽  
Analytical Formulae ◽  
Definition Of

The results of a number of laboratory tests of wind-driven fires indicate the existence of a characteristic wind speed, U'. The form of the fire spread (V) as a function of mid-flame wind speed (U) differs above and below this characteristic speed. The scatter in field data is so great that it is difficult to confirm this result for field data. However, expressions of the form: V/V0 -1 = α(U/U')0.5 U/U' < 1 and V/V0 -1 = α(U/U')3 U/U' > 1 with U' = 2.5 m s-1 perform in a similar manner to existing models. For many fuel types α = 15. A difficulty with existing fire spread models is the measurement and definition of V0, the no-wind rate of spread. It can hardly ever be measured in the field and has to be inferred from analytical formulae, or by extrapolating measured data. The value of a depends on the method used estimate V0.

scholarly journals Evaluation of WRF-SFIRE performance with field observations from the FireFlux experiment

2013 ◽  
Vol 6 (4) ◽  
pp. 1109-1126 ◽  
Author(s):  
A. K. Kochanski ◽  
M. A. Jenkins ◽  
J. Mandel ◽  
J. D. Beezley ◽  
C. B. Clements ◽  
...  
Keyword(s):  
Wind Speed ◽  
Ground Level ◽  
Surface Flow ◽  
Horizontal Wind ◽  
Temperature Structure ◽  
Fire Plume ◽  
Arrival Times ◽  
Wind Speeds ◽  
Rate Of Spread ◽  
Fire Front

Abstract. This study uses in situ measurements collected during the FireFlux field experiment to evaluate and improve the performance of the coupled atmosphere–fire model WRF-SFIRE. The simulation by WRF-SFIRE of the experimental burn shows that WRF-SFIRE is capable of providing realistic head-fire rate of spread and vertical temperature structure of the fire plume, and fire-induced surface flow and vertical velocities within the plume up to 10 m above ground level. The simulation captured the changes in wind speed and direction before, during, and after fire front passage, along with the arrival times of wind speed, temperature, and updraft maxima, at the two instrumented flux towers used in FireFlux. The model overestimated vertical wind speeds and underestimated horizontal wind speeds measured at tower heights above 10 m. It is hypothesized that the limited model spatial resolution led to overestimates of the fire front depth, heat release rate, and updraft speed. However, on the whole, WRF-SFIRE simulated fire plume behavior that is consistent with FireFlux observations. The study suggests optimal experimental pre-planning, design, and execution strategies for future field campaigns that are intended to evaluate and develop further coupled atmosphere–fire models.

Prediction of Atmospheric Turbulence Characteristics for Surface Boundary Layer using Empirical Spectral Methods

2020 ◽  
Author(s):  
Yagya Dutta Dwivedi ◽  
Vasishta Bhargava Nukala ◽  
Satya Prasad Maddula ◽  
Kiran Nair
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Surface Roughness ◽  
Wind Speed ◽  
Atmospheric Turbulence ◽  
Surface Boundary ◽  
Low Frequencies ◽  
Surface Boundary Layer ◽  
Power Spectral ◽  
Mean Wind Speed

Abstract Atmospheric turbulence is an unsteady phenomenon found in nature and plays significance role in predicting natural events and life prediction of structures. In this work, turbulence in surface boundary layer has been studied through empirical methods. Computer simulation of Von Karman, Kaimal methods were evaluated for different surface roughness and for low (1%), medium (10%) and high (50%) turbulence intensities. Instantaneous values of one minute time series for longitudinal turbulent wind at mean wind speed of 12 m/s using both spectra showed strong correlation in validation trends. Influence of integral length scales on turbulence kinetic energy production at different heights is illustrated. Time series for mean wind speed of 12 m/s with surface roughness value of 0.05 m have shown that variance for longitudinal, lateral and vertical velocity components were different and found to be anisotropic. Wind speed power spectral density from Davenport and Simiu profiles have also been calculated at surface roughness of 0.05 m and compared with k−1 and k−3 slopes for Kolmogorov k−5/3 law in inertial sub-range and k−7 in viscous dissipation range. At high frequencies, logarithmic slope of Kolmogorov −5/3rd law agreed well with Davenport, Harris, Simiu and Solari spectra than at low frequencies.

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