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The present study focuses on the flow field characterization of highly turbulent premixed flames, typical for stationary gas turbines. Mean flame front position and flame front structure at high inlet temperatures, lean mixtures, and high pressures are studied, too. Turbulence intensities and integral length scales have been measured in an isothermal flow field with the help of Particle Image Velocimetry (PIV). Mean flame front position and flame structure have been studied using Planar Laser-Induced Fluorescence (PLIF) of the OH radical. Turbulence intensities and integral length scales have been measured for different turbulence generating grid geometries and operating conditions. The results show that the combustor flow field can be divided in a region close to the combustor head, where grid-generated turbulence is dominant, and a region further downstream, strongly influenced by turbulence generated in the shear layer. In general the measured turbulence intensity scales well with the bulk velocity. For a systematic variation of the turbulent Reynolds number, Damko¨hler number, and Karlovitz number the mean flame front position and the flame front structure were investigated. Increasing the pressure and thereby mainly increasing the turbulent Reynolds number only slightly affects the mean flame front position but increasingly corrugates the flame front. Increasing the bulk velocity and thereby the turbulence intensity does not affect the mean flame front position but due to the higher turbulence the flame front is increasingly corrugated.

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The present experimental study focuses on flame characteristics and turbulent flame speeds of lean premixed flames typical for stationary gas turbines. Measurements were performed in a generic combustor at a preheating temperature of 673 K, pressures up to 14.4 bars (absolute), a bulk velocity of 40 m/s, and an equivalence ratio in the range of 0.43–0.56. Turbulence intensities and integral length scales were measured in an isothermal flow field with Particle Image Velocimetry (PIV). The turbulence intensity (u′) and the integral length scale (LT) at the combustor inlet were varied using turbulence grids with different blockage ratios and different hole diameters. The position, shape, and fluctuation of the flame front were characterized by a statistical analysis of Planar Laser Induced Fluorescence images of the OH radical (OH-PLIF). Turbulent flame speeds were calculated and their dependence on operating conditions (p, φ) and turbulence quantities (u′, LT) are discussed and compared to correlations from literature. No influence of pressure on the most probable flame front position or on the turbulent flame speed was observed. As expected, the equivalence ratio had a strong influence on the most probable flame front position, the spatial flame front fluctuation, and the turbulent flame speed. Decreasing the equivalence ratio results in a shift of the flame front position farther downstream due to the lower fuel concentration and the lower adiabatic flame temperature and subsequently lower turbulent flame speed. Flames operated at leaner equivalence ratios show a broader spatial fluctuation as the lean blow-out limit is approached and therefore are more susceptible to flow disturbances. In addition, because of a lower turbulent flame speed these flames stabilize farther downstream in a region with higher velocity fluctuations. This increases the fluctuation of the flame front. Flames with higher turbulence quantities (u′, LT) in the vicinity of the combustor inlet exhibited a shorter length and a higher calculated flame speed. An enhanced turbulent heat and mass transport from the recirculation zone to the flame root location due to an intensified mixing which might increase the preheating temperature or the radical concentration is believed to be the reason for that.

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