The Dynamics and Structure of Turbulent Premixed Flames: Flame-Vortex Interaction and Experimental Optical Diagnostics

Modern propulsion and power generation technology operates under highly turbulent conditions to promote increased efficiency. The coupled relationship between the turbulence conditions and imposed pressure gradients on reacting flow dynamics are explored by decomposing the vorticity transport terms to quantify the vorticity budgets under varying conditions. This is performed on a bluff-body reacting flow-field by utilizing the two-dimensional diagnostics of particle image velocimetry (PIV) and CH* chemiluminescence to allow for a resolved velocity field and flame front. The vorticity budget is determined by utilizing a mean conditional fluid element tracking procedure to quantify the evolution of the individual vorticity terms through the flame front. The results indicate that the flow-field is more sensitive to turbulence conditions, which when increased promote a shift towards flow-field dynamics resembling non-reacting conditions with the exothermic term contributions diminished. Additionally, since the turbulent dynamics in reacting flow-fields create strong three-dimensional behaviors tomography is implemented to capture three-dimensional flow-field and flame structure. A fiber-based endoscope method is implemented to capture multiple viewpoints simultaneously on a single camera sensor to examine the efficacy and limitations of the approach for reacting flows. Tomographic PIV and CH* chemiluminescence measurements are captured for a Bunsen flame and compared to traditional two-dimensional measurements. The PIV measurements indicate that there is agreement between the measurement techniques when considering the average velocity and vorticity fields. However, there is increased divergence when examining the instantaneous terms. The CH* chemiluminescence revealed that the measured intensity gradients are similar although there is considerable warping in the of the flame geometry near the base of the burner which diminishes near the center of the flame height. Lastly, optimal viewing angles are determined utilizing luminescent molds to help mitigate any warping errors which were encountered when conducting chemiluminescence measurements