Intermittency Dynamics of Bluff-Body Flames in High Intensity Turbulence

Premixed flames stabilized in propulsion and power generation engines act as a self-propagating surface, the dynamics of which become stochastic in fields of high intensity turbulence. To better characterize the localized dynamics of premixed flames, the intermittency of turbulent bluff-body flames are experimentally analyzed across a range of inlet turbulence conditions, spanning a Karlovitz number range between 1-132. The response of the flame surface to inlet turbulence is quantified by high-speed, time-resolved particle image velocimetry and C2*/CH* chemiluminescence diagnostics. Spectral analysis of the local flame oscillations, and their corresponding probability density functions are compared to gaussian distributions to assess the degree of intermittency on both large and small scales. Increased turbulence intensities alter the oscillatory dynamics of the flame surface, and the local flame surface experiences more burst from the time-average flame position. The small-scale intermittency of the flame is characterized by structure functions comparing the flame oscillation at different temporal increments. Although the oscillatory dynamics, advection, and distortion of the flame are altered with increased turbulence intensities, the results show that intermittent nature of the flame may become self-similar in confined propulsion and energy production environments. The implications of the results for advanced modeling of highly turbulent premixed flames are also discussed.