Modelling aerodynamics and combustion of firebrands in long-range spotting

Abstract

During a wildfire, parts of the vegetation such as twigs or bark can detach, ignite and become firebrands or embers. When they travel ahead from the main fire front, they can ignite secondary fires in a process known as spotting. We introduce pyBrands, an open-source python tool that uses coupled fire-atmosphere simulations to calculate firebrand trajectories. This module integrates aerodynamic and combustion models for firebrands. This study compares the existing drag and lift models, and combustion models for firebrands by simulating a realistic wildfire plume in a large numerical domain. Firebrands with different properties were injected into the plume and their landing densities were compared. Results indicate that travelled distances strongly depend on the aerodynamic and combustion model. This makes the choice of models difficult and impractical due to the required time step. pyBrands could be used to test and develop new models, improving firebrand behavior prediction in wildfires.