Flame-Turbulence Interactions in a Freely-Propagating, Premixed Flame

Abstract

Previous experimental investigations of turbulence measurements in conventional laboratory premixed flames are extensively reviewed. Because of numerous disadvantages of these configurations, primarily associated with flame stabilization mechanisms, a freely-propagating flame configuration is proposed for the study of flame-turbulence interactions. The unperturbed, unrestrained flow field in this configuration is ideal for measuring the effect of the flame on turbulence properties. Temporally resolved, ensemble averaged measurements of turbulence intensity, integral length scale, integral time scale, and energy spectrum have been measured both normal and parallel to the mean flame surface with laser Doppler velocimetry (LDV) in a propane-air flame at an equivalence ratio of 1.0, in a flow with incident turbulence intensity of 25 cm/s and length scale of 8 mm. The following changes in turbulence parameters were observed across the flame: a factor of five to six increase in the normal turbulence intensity, a factor of two to three increase in the parallel turbulence intensity, a factor of two increase in the density weighted lubulent kinetic energy, a 100% increase in the normal length scale, a 50% increase in the parallel length scale, an increase in turbulence time scale, and a slight shifting of turbulence energy towards lower frequencies in the normal component. These results indicate that turbulence production in the flame is significant, and is anisotropic in nature