Date of Award

2020

Document Type

Thesis

Degree Name

Master of Science in Engineering (MSE)

Department

Mechanical and Aerospace Engineering

Committee Chair

Shankar Mahalingam

Committee Member

Babak Shotorban

Committee Member

Kader Frendi

Subject(s)

Wildfires--Research., Flame spread--Testing., Adenostoma.

Abstract

The current work focuses on better understanding of the phenomenon of fire interactions between multiple burning chamise shrubs. The Wildland-Urban Interface Fire Dynamics Simulator (WFDS , Mell et al. 2009) was utilized to study burning behavior of 1 m tall, 0.7 m maximum diameter chamise shrubs. All shrubs were simultaneously ignited from their bases by individual ignition zones located on the ground beneath the shrubs. Two separate shrub arrangements were investigated. First, nine shrubs were placed in a 3 × 3 horizontal array arrangement. Several simulations were performed by varying the shrub separation distance and wind speed. Two competing interaction mechanisms were identified: heat feedback enhancement, primarily due to thermal radiative heating, and air entrainment restriction. The burning characteristics of the shrubs were examined as well as a global average burning rate was introduced and analyzed. For the no wind condition, the peak mass loss rate of the center shrub is 23\% higher than the rest of the shrubs, indicating that the heat feedback enhancement is dominant. However, air entrainment causes the surrounding shrubs to burn less intensely. At an imposed wind speed, air entrainment effects are dominant. The shrubs that are best shielded from the higher wind speeds are the shrubs that burn most intensely. Second, two shrubs were placed adjacent to each other, and the vertical separation between them was varied. Several simulations were performed by varying the vertical position of one of the shrubs and varying the wind speed. With no ambient wind, no interaction between the two shrubs was observed, and their behavior was similar to a single isolated shrub. However, with an ambient wind speed of 1 m/s, significant interaction between shrubs occurred due to flame-tilting. The downwind shrubs burned the most vigorously of all shrubs simulated for vertical separations between 0.2 and 0.8 meters.

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