Turbulence measurements in a propagating, premixed flame

An experimental study was conducted to illuminate the interaction between turbulence and premixed flames. This was accomplished by extensively characterizing the turbulence field in both the upstream and downstream regions of a premixed propane flame. The response of the turbulence field to combustion heat release was indicated by changes in averaged turbulent parameters.; A new flame configuration was proposed and developed in this study. It consisted of an unstabilized, freely propagating flame in an open, quartz-walled test section. The flame was statistically one-dimensional and avoided the spurious interferences from stabilization mechanisms that are normally associated with stationary flames. The range of incident turbulence Reynolds number approached one thousand. The upstream conditions resided in the multiple flamelet regime of turbulent combustion. Because of the high turbulence, the flame structure consisted of very fine detail. Four separate flame conditions were studied, revealing dependencies on both incident turbulence level and combustion heat release.; The turbulence was measured with a two-point laser Doppler velocimeter. The turbulence parameters were determined by ensemble-averaging data from hundreds of flame events. The calculated parameters included turbulence intensities, autocorrelations, integral time and length scales, and energy spectra; all quantities were measured both normal and parallel to the mean flame surface. The data represents the most complete turbulence characterization in any premixed flame to date, and the first report of turbulence length scales in a reacting flow determined directly from the two-point spatial correlation.; The effects of combustion on the turbulence field were dramatic. Turbulence intensities increased by several factors. The increase scaled with both incident turbulence level and heat release. The increase in the component normal to the flame was typically twice that of the parallel component. Anisotropy was also indicated by the integral length scale; the parallel scale roughly doubled while the normal component increased by an order of magnitude. The integral time scales experienced much milder changes, and only in the lower Reynolds number cases. The spectral structure of the normal component was largely unaffected by the flame, but the parallel component increased in slope.