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Abstract
Previous planar imaging measurements in lifted, turbulent jet flames provide evidence for the three-dimensionality of these flows and the importance of flame propagation in the azimuthal direction normal to the image plane. The primary objective of the present paper is to obtain data in a plane normal to the flow direction that will provide a better understanding of the three-dimensional features of the flow. In addition, the results of the previous measurements were limited to a Reynolds number of 7,000. imaging data at a Reynolds number of 12,100 will be presented to extend the previous findings to a higher Reynolds number regime. Images of the radial cross section in the low Reynolds number flame show that considerable asymmetry and structure exist. At upstream locations, the flame is typically not continuous around the circumference of the jet but consists of multiple flame segments. Farther downstream, the flame extends over a larger percentage of the circumference with breaks confined to smaller lengths along the circumference. The CH chemiluminescence images show numerous breaks in the flame sheet. These breaks coincide with outward bulges in the flame sheet that result from the formation of vortical structures in the jet shear layer. The images clearly show the three-dimensionality of the flow, since the breaks in the flame are localized to the area of the bulges and do not extend around the circumference of the central jet. Many of the same features found in the lower Reynolds number flame are also seen at the higher Reynolds number. Consistent with the larger turbulence scales existing farther downstream where this flame is stabilized, the flame surface is more convoluted and breaks in the flame sheet are more extensive. Rapid discontinuous jumps upstream by the flame are seen considerably more often than in the lower Reynolds number flame, which is indicative of the higher turbulence levels and greater three dimensionality of this flame.
