Simulation Study and Proper Orthogonal Decomposition Analysis of Buoyant Flame Dynamics and Heat Transfer of Wind-Aided Fires Spreading on Sloped Terrain
Abstract
1. Introduction
2. Computational Methods
2.1. Gas-Phase Governing Equations
2.2. Vegetation Fuel Model
2.3. The Principle of Proper Orthogonal Decomposition
2.4. Experiments and Numerical Setup
3. Results and Discussion
3.1. Fire Perimeter and Rate of Spread (ROS)
3.2. Flow Field and Perturbation Pressure
3.3. Flame Morphology
3.4. Radiative and Convective Heat Transfers
3.5. Proper Orthogonal Decomposition (POD) Analysis
4. Conclusions
- A power-law relationship was found between the ROS and slope angle. It was revealed that in high-slope conditions, the convergence of incoming wind and the weakened indraft air from the frontal area made a significant contribution to the abrupt rise in ROS and the eruptive spread of the head fire. As the slope increased, the flame also approached the combustible material under the action of gravity. As the slope gradually increased, the flame eventually coincided with the combustible material ahead, leading to a rapid increase in convective heat transfer.
- The enlarged volume of the fire plume was deemed to enhance the radiation heat transfer, and in contrast, the higher possibility of flame attachment at higher slopes (especially >20°) led to the prominent role of convective heating. When a flame attached to a wall, convective heat transfer significantly increased compared to radiative heat transfer.
- The investigation into the joint temperature–velocity field utilizing a POD approach revealed an increased forward pulsation of the flame front with the escalating slope, leading to a higher energy density in the pre-combustion zone ahead of the fire line, which further explained the mechanism underlying the accelerated flame propagation.
- For wildfire modeling, the more decent model should distinguish the respective roles of wind and slope, where the slope has a more profound effect in terms of determining flame structures and convective heat; the unsteady feature of flame puffing could be incorporated, considering the dominated mode pattern of backward–forward pulsation.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
Nomenclature
Gas density | |
Velocity vector | |
Viscous stress | |
Drag force by the fuel particles | |
Vorticity vector | |
Pressure perturbation | |
Species diffusion coefficients | |
Mass increment due to particle degradation | |
Energy from the chemical reactions | |
Heat release rate | |
Energy transferred to particles | |
Accounts for subgrid heat fluxes of conduction and radiation | |
M | Fuel moisture content |
Absorption coefficient | |
Shape factor | |
Stefan–Boltzman constant | |
The endothermic effect of water evaporation | |
Heats associated with pyrolysis and char oxidation | |
Surface area to the volume ratio | |
Packing ratio | |
h | Convective heat transfer coefficient |
Fuel mass | |
Concentration of fuel | |
A | Pre-exponential factor |
Activation energy | |
R | Universal gas constant |
T | Gas temperature |
Appendix A
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Fuel Parameter (Units) | Value |
---|---|
Fuel density () | 780 [14] |
Fuel load () | 0.4 [14] |
Fuel height (m) | 0.08 [14] |
Surface-to-volume ratio (1/m) | 3800 |
Fuel moisture (%) | 10 [14] |
Heat of combustion (kJ/kg) | 17,700 [14] |
Specific heat (kJ/(kg·K)) | 1.2 |
Conductivity (W/(m·K)) | 0.1 |
Ambient temperature (K) | 304 [14] |
Vegetation char fraction (-) | 0.2 [14] |
Relative humidity (%) | 40 [14] |
Radiation fraction (%) | 0.342 [14] |
0.5 m/s | ✓ | ✓ | ✓ | ✓ | ✓ |
1.0 m/s | ✓ | ✓ | ✓ | ✓ | ✓ |
1.5 m/s | ✓ | ✓ | ✓ | ✓ | ✓ |
0.5 m/s | 1.0 m/s | 1.5 m/s | |
---|---|---|---|
122.6 | 24.4 | 9.8 | |
164.9 | 27.3 | 12.6 | |
194.4 | 32.9 | 15.9 | |
247.9 | 83.3 | 18.2 | |
526.1 | 103.0 | 27.8 |
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Su, C.; Hu, Y.; Ma, Y.; Yang, J. Simulation Study and Proper Orthogonal Decomposition Analysis of Buoyant Flame Dynamics and Heat Transfer of Wind-Aided Fires Spreading on Sloped Terrain. Fire 2025, 8, 139. https://doi.org/10.3390/fire8040139
Su C, Hu Y, Ma Y, Yang J. Simulation Study and Proper Orthogonal Decomposition Analysis of Buoyant Flame Dynamics and Heat Transfer of Wind-Aided Fires Spreading on Sloped Terrain. Fire. 2025; 8(4):139. https://doi.org/10.3390/fire8040139
Chicago/Turabian StyleSu, Chenyao, Yong Hu, Yiwang Ma, and Jiuling Yang. 2025. "Simulation Study and Proper Orthogonal Decomposition Analysis of Buoyant Flame Dynamics and Heat Transfer of Wind-Aided Fires Spreading on Sloped Terrain" Fire 8, no. 4: 139. https://doi.org/10.3390/fire8040139
APA StyleSu, C., Hu, Y., Ma, Y., & Yang, J. (2025). Simulation Study and Proper Orthogonal Decomposition Analysis of Buoyant Flame Dynamics and Heat Transfer of Wind-Aided Fires Spreading on Sloped Terrain. Fire, 8(4), 139. https://doi.org/10.3390/fire8040139