Experimental studies of fire-atmosphere interactions during grass fires

Measurements of fire-atmosphere interactions are very limited. This limitation is due to the extreme difficulty of making measurements in the fire environment. Experimental studies were conducted to gain a dynamical understanding of fire-atmosphere interactions associated with grass fires. These experiments used a number of instrument platforms placed within the fire perimeter. Data showed that the flows and turbulence were complex. Turbulence generated near the combustion zone was anisotropic and formed as a result of strong horizontal variance in the ambient wind direction. Turbulence in the upper plume was more isotropic and was associated with stronger buoyancy. Winds during fire front passage were two to three times greater than the ambient flow. Strong downdrafts were observed to occur behind the fire front and were associated with the entrainment of ambient air into the fire plume. In addition, downdrafts were observed ahead of the fire front and these were associated with the formation of a horizontal vortex. Ahead of the fire front a weak convergence zone formed and winds in this zone were less in magnitude than the ambient winds. Wind direction in the convergence zone shifted from ambient northerly direction to southerly indicating inflow into the approaching fire front. These experiments show that measurements within the fire zone can lead to useful data for better understanding fire-atmosphere interactions.