Post-Landing Firebrand Dynamics in Topography-Driven Turbulence*

During wildfires, a substantial number of smoldering particles, referred to as firebrands, are produced and carried downwind by the wind. Once landed, they can ignite secondary fires even several kilometers ahead of the main fire front. This phenomenon, known as spotting, can amplify the rate at which wildfires propagate, thereby increasing the vulnerability of wildlife and communities, and reducing the effectiveness of fire suppression efforts.

Firebrands are transported through a complex interplay between particles and turbulence at every stage of their trajectory, from being lofted into the air to their final landing. Once they land, firebrands move based on their characteristics and the conditions of the near-surface airflow and may create accumulation zones that increase the risk of secondary fires. The accurate prediction of firebrand dispersal and accumulation is, therefore, important for fire risk assessments and management practices, especially in wildfire-prone communities. This work develops a Lagrangian particle-tracking model to investigate the mechanisms controlling firebrand particle dispersal and accumulations in topography-induced turbulence. Firebrands are represented as spherical particles with time-varying mass, size, and temperature, and are tracked across different turbulent flows simulated using Large-Eddy Simulations. Particle ground-level behaviors are investigated under different conditions and the results are compared against experimental results.