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.