"Ember transport and accumulation in WUI fires"
Apr 7, 2021 Schedule:
- Virtual Tea Time
- 03:00 to 03:30 PM Eastern Time (US and Canada)
- Virtual Colloquium
- 03:30 to 04:30 PM Eastern Time (US and Canada)
Embers landing on and around buildings are one of the leading causes of home destruction during wildfires. Embers form from combusting debris breaking off from burning vegetation. They are then lofted into the atmosphere by the fire plume, transported ahead of the fire by the wind, fall to the ground and can then cause spot fires. This talk will cover two components of this problem, windborne transport and accumulation on rooftops. Experimental and modeling results will be presented for the three-dimensional 6-Degree-of-freedom flight of embers in a turbulent wind field. Results show that quasi-steady force coefficients can adequately predict the distribution of landing locations for lofted embers even in a highly turbulent unsteady flow. Experimental results will also be presented that quantify the stability of embers at rest on a rooftop. The stability of embers is controlled by the flow separation of the wind flowing over and around the building as well as the building geometry and wind speed. Finally, the talk will present preliminary results on the accumulation of windborne embers on a range of building shapes. The results demonstrate that rooftop shape is a major contributing factor in accumulation rates and spot fire risk with more complex roof shapes being more prone to ember accumulation.