CAREER: Multiscale Firebrand Transport in the Turbulent Boundary Layer for Fire Science Advancement

Wildfires have become a common occurrence in the U.S. and around the world. The costs of wildfires are magnified when they spread into communities; commonly referred to as wildland-urban interfaces (WUI). In wildfires, fragments of burning materials, known as firebrands (or flying embers) can be generated, lofted, and carried by the wind several meters to kilometers ahead of the main fire-front and create several new spot fires.

Post-fire studies indicated that firebrands are responsible for the fastest spread and the major cause of the ignitions in WUIs. From the moment an ember becomes airborne, a firebrand’s trajectory, and thus its landing spot, depends on characteristics of the turbulent wind flow. While the structure of the turbulent winds is determined by mechanical and buoyant forces, there is currently no clear fundamental understanding of how these factors affect the spotting risks.

In addition, it is not clear what role the small eddies of the turbulent flow play in determining firebrand behavior because their effects are neglected in the majority of physics-based studies. The principle aim of this project is to advance fluid-dynamic understanding of the firebrand transport phenomenon in turbulent winds, increase the general public’s scientific literacy about fire safety, and motivate a wide spectrum of students to engage in this emerging field.

This research will advance the prediction and mitigation of fire spread into wildfire-prone areas and elevate the importance of fire science in the national landscape.

The research will use Large-Eddy Simulations, Lagrangian particle tracking of the embers, and surface energy balance analyses to systematically investigate the effect of the turbulent scale interactions on firebrand transport and spotting risk for the advancement of fire science. The project will, for the first time, a) develop and validate a versatile multiscale computational model of firebrand transport that incorporates the important effects of small scale turbulence (i.e., the order of the size of the embers) on evolving firebrands; b) investigate the effect of thermally-driven turbulent winds due to heterogeneous spatiotemporally variable buoyant forces on firebrand transport, and c) explore the effect of mechanically-driven turbulence structures due to surface topography on firebrand transport.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.