Our Spring Quarter WIldfire Research and Policy Seminar Series continues this week with a talk by Hayoon Chung. She will speak about an experimental study of parameters affecting Firebrand Transport.

Abstract

Despite the significant role of spot-fire spread in wildfires, there is a general lack of understanding of what parameters control the transport of firebrands. Using our background in environmental fluid mechanics, we aimed to test the impact of various physical parameters (that are often disregarded in spotfire literature) on firebrand transport. We focused on testing the relevance of four physical parameters: the shape of the firebrands (modeled using particles), the nature of the buoyant thermal plumes that loft the firebrands, gaps in the tree canopy, and the strength of the crosswind and ambient canopy turbulence. 

Our study was conducted experimentally in a recirculating (water) flume with model vegetation, plume and particles (embers). We tested for the impact of each parameter (plume intensity, canopy-turbulence intensity, gap-recirculation dynamics) on firebrand transport by releasing model particles into characteristic flows and comparing the particles’ behavior. Using PTV (Particle Tracking Velocimetry), we observed particle landing distribution, and spatial/temporal variations of position, velocity, and acceleration. Results suggest that ambient turbulence, due to the presence of large-scale rollers at the canopy/crossflow interface, can affect the distribution of the particle settling distances. Furthermore, the recirculation patterns in the wake of canopies can also alter the particle’s settling patterns. We also find that in addition to their role in the initial lofting of the particles, the nature of the buoyant plumes at the time of lofting have a strong influence on where the particles settle.