Entrainment measurements in turbulent buoyant jet flames and implications for modeling

Abstract

Air entrainment rates were measured along turbulent buoyant jet flames having heat release rates up to 45 kW and nozzle diameters 12 mm and 23 mm. We used the Ricou-Spalding measurement technique which involves supplying just enough ambient air to an enclosure around the flame to produce zero pressure drop across an exit orifice plate. The experimental enclosure, the orifice plate and the pressure lines were water-cooled because of the large radiative output from the fires. The entrainment rates at various positions in the turbulent flame for the larger nozzle (23 mm dia) were independent of the total heat release rate (20 kW, 31 kW and 45 kW) and increased with the 5/2 power of the distance from the nozzle exit. Similar behavior was observed for the smaller nozzle but with a virtual origin some distance above the nozzle exit. Implications of the present results for mathematical modeling of turbulent burning are discussed in conjunction with the heat release rates along turbulent buoyant jet flames.