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Dynamic Processes in Fundamental and Applied Turbulent Combustion

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Results will be discussed from investigations into dynamic turbulent combustion phenomena using high‐speed planar laser diagnostics. In the first investigation, the processes of flame surface straining and wrinkling that occur as turbulence interacts with a premixed flame were studied using highspeed particle image velocimetry. It was shown that the standard method of characterizing turbulence‐flame interactions based on vortical structures is insufficient to describe the strain‐rate exerted on a flame; coherent structures of fluid‐dynamic strain‐rate also must be considered. Furthermore, the geometry of the interaction significantly affected the flame response, precluding the use of simplified configurations to develop turbulent combustion simulation models. Based on these observations, empirical relationships were developed for important terms in such models. These relationships showed distinct dependencies on the scale and configuration of the turbulence. In the second investigation, high‐speed particle image velocimetry and OH planar laser induced fluorescence were used to study the dynamics of a gas‐turbine‐like confined swirl flame. Heat release fluctuations were found to occur at the acoustic frequency; however, the flame was operated in a ‘quite’ mode in which these fluctuations did not couple to produce a thermo‐acoustically unstable system. The method of spatio‐temporal proper orthogonal decomposition was used to determine the dynamics of the dominant flow features, while important heat release metrics were determined by mapping the flame topography from the OH PLIF images. It was found that the dominant flow structure was a helical vortex core that precessed around the burner nozzle at a frequency that was independent from the combustor acoustics. However, various metrics of the heat release, some caused by turbulence‐flame interaction, fluctuated at the acoustic frequency. By studying the frequency and phase of these processes, a coherent picture of the combustor dynamics was developed.

This talk is part of the Engineering Department Energy, Fluids and Thermo seminars series.

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