A computational study of the interactions of three adjacent burning shrubs subjected to wind

A three-dimensional physics-based model was used to investigate the effect of shrub size, shrub separation distance and wind on the burnout times of shrubs. The shrub considered for this study was chamise. Two shrub sizes with different physical dimensions and initial masses with two wind speeds were considered. The study was performed for an array of three shrubs with separation distances ranging from zero to one shrub diameter. The shrubs were situated at the vertices of an equilateral triangle with two shrubs placed upwind (upstream shrubs) of the third shrub (downstream shrub). For a smaller shrub and a higher wind speed, the direction of fire front propagation within the shrub was found to be opposite to the direction of the wind, which resulted in a longer burning time for the shrub. For larger shrubs, a decrease in burning time was observed with an increase in wind speed. The burnout time for upstream shrubs increased with an increase in shrub separation distance for all shrub sizes and wind speeds considered. The burnout time for the downstream shrub was found to decrease with an increase in the separation distance, reach a minimum, and then increase with an increase in separation distance. The trends observed in burnout times for downstream shrub were attributed to the balance between heat feedback into the downstream shrub from the flames in upstream shrubs and availability of sufficient oxygen for combustion to take place.