The Turbulent Structure of a Wildland Fire

We report measurements of temperature and wind during the passage of a flame front in California chaparral. The instruments were three component water-cooled anemometers and radiation compensating thermocouples mounted at three and sever meters. Data was recorded on ballistic recorders. This system is described elsewhere. The response lenght of the anemometers was one meter. Response time of the radiation compensating thermocouples is complicated but is about two seconds.

Fuel loadings were seventy-five tonnes per ha. The experimental area was three of three meter high chamise. Fuel loadings were seventy-five tonnes per ha. The experiments were conducted at an altitude of 1700 meters on Mount Palomar, San Diego County, California. Ambient winds varied between two and four meters per second. Ignition was with drip torches.

Characteristics of the flame front indicate that it behaved as a soliton. Winds from behind the fire provided little air to the flames, but were important in determing the speed of propagation of the flames. Winds immediately ahead of the fire had a downward component on the order of fifty meters per second. The in-flame winds had upward speeds as great as seventy meters per second. Winds following the fire were about the same as the ambient flow. Spectral analysis of the fire winds will be presented.