Urban Geometries and Their Role in Modulating Ember Dispersion and Spotting

Firebrand spotting, the lofting and transport of burning particles ahead of a wildfire, is a major driver of rapid fire spread. In Wildland-Urban Interface (WUI) fires, urban topography alters local wind and turbulence fields, significantly impacting firebrand trajectories and landing behavior. Using Large Eddy Simulations, we model turbulent flow over idealized urban layouts composed of cubic obstacles and analyze their influence on firebrand dispersion. Spherical firebrands, treated as mass- and size-evolving particles, are randomly released and tracked using a Lagrangian particle model. Flow and particle statistics across various building densities, heights, and arrangements are compared to assess impacts on flight distance, spatial spread, and thermal state at landing. Results show that denser and taller layouts reduce average flight distances due to wind blockage, but increase turbulence intensity, resulting in wider dispersion and greater variability in deposition patterns, especially for smaller firebrands. This study highlights the critical role of urban form in firebrand transport and provides insights for designing fire-resilient WUI communities.