| 01 Jun 2026
Evaluation of angular resolution of the finite volume method on the predicted accuracy of wildfire thermal radiation
Abstract. Thermal radiation is the dominant heat transfer mechanism in wildfires, governing both flame dynamics and fire spread through radiative preheating of unburned fuels. In physics-based wildfire models, the Finite Volume Method (FVM) is widely used to solve the 3D Radiative Transfer Equation. However, a fundamental contradiction exists between the demand for high-fidelity incident radiation predictions and the associated computational overhead. While previous research has predominantly focused on buoyancy-driven flames, this study systematically evaluates the impact of FVM angular resolution on the accuracy of surface incident radiation for both buoyancy-driven and wind-driven fire scenarios. Results show that low-resolution schemes (e.g., 16 azimuthal and 2 zenith angles) suffer from severe "ray effects"—non-physical numerical oscillations—leading to significant local heat flux errors. In calm atmosphere cases, a high resolution of at least 64–12 angles is required to eliminate artifacts and resolve the incident radiation correctly. In wind-driven scenarios where the flame is attached to the surface, the high-intensity radiation zone near the fire source is more tolerant of lower resolutions (e.g., 32-4), though far-field predictions remain sensitive. This research provides critical selection guidelines for angular discretization in wildfire radiation models.
The manuscript investigates the effect of angular resolution in the finite volume method on predicted surface incident radiation in wildfire radiation modeling. This is a relevant and useful topic, since angular discretization directly affects ray effects, heat-flux accuracy, and computational cost. The authors compare buoyancy-driven and wind-driven fire cases and provide practical recommendations for selecting angular resolution. The objective is clear, and the decoupled radiation-only approach is appropriate for isolating the numerical influence of angular discretization. However, the authors should address following comments before publication:
Major comments:
(1) The manuscript appears to use 64-12 as the reference or converged solution. Please clarify whether this case is truly angular-converged or simply the finest resolution tested. If no finer case was tested, the statement should be softened.
(2) The findings show that buoyancy-driven and wind-driven flames show different sensitivity to angular resolution. The authors should more clearly explain why the attached flame in the wind-driven case is less sensitive near the fire source, whereas the detached and unsteady buoyant flame requires finer angular discretization.
(3) The decoupled approach is reasonable for isolating angular-discretization effects. However, the statement that this strategy does not affect the purpose may be too strong. In fully coupled wildfire spread simulations, radiation can influence fuel preheating, pyrolysis, flame dynamics, and spread rate. This limitation should be stated more carefully.
(4) Tables 1 and 2 provide useful timing and memory information, but the timing trends are not entirely clear. For example, in the windy case, the 48-8 case appears faster than the 40-6 case. The authors should specify whether the reported values are wall-clock time or CPU time, and whether the processor number, decomposition strategy, and solver settings were identical.
Minor comments:
(1) Please define the angular-resolution notation, such as 16-2, 32-4, and 64-12, clearly at first use and in figure captions.
(2) Some conclusions use strong wording such as “ray effects vanish.” Unless a quantitative criterion is provided, it may be better to write “ray effects become visually negligible” or “are substantially reduced.”
(3) The limitation related to non-sooting flames is important and should be mentioned earlier in the methodology, not only in the conclusion.
(4) Several language issues should be corrected, for example: “unburn vegetables” to “unburned vegetation/fuels,” “The chose of numbers” to “The choice of the numbers,” “buoyance driven” to “buoyancy-driven,” and “Keven-Helmholtz” to “Kelvin–Helmholtz.”