Understanding the role of buoyancy and inertia in wind-aided vegetative fires

The combined effects of buoyancy and inertia forces are studied for wind-aided vegetative fires. Two fuels - Pinus palustris ( PP ) and Pinus rigida ( PR ) are tested at five different wind conditions. The flame geometrical parameters are normalized using the flame height and scaled against the inverse of the Froude number ( Fr ). A power-law relationship is observed between all the flame geometrical parameters and 1 / Fr . The instantaneous rate of spread is calculated using an image analysis algorithm by separating flame impingement and flame spread. The behavior of the average rate of spread is explored by evaluating radiative heat flux in the preheating region. The fluctuating rate of spread ( R ′ ) is calculated from the instantaneous and average rate of spread values. The spectral analysis of R ′ shows a range of frequencies that are an integer multiple (or harmonics) of the characteristic frequency for a given experiment. Strouhal number (St) evaluated using the characteristic frequency multiplied by the leaf area index of the pine needle bed shows a linear behavior against 1 / Fr . • A technique is developed to separate flame impingement from flame spread. • Mean flame geometry shows a non-linear behavior against the inverse of Froude number. • The fluctuating rate of spread occurs at various harmonic frequencies. • The Strouhal number varies linearly with the inverse of Froude number.