Role of Buoyancy on Instabilities and Structure of Transitional Gas Jet Diffusion Flames |
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Authors: | P S Kolhe A K Agrawal |
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Institution: | (1) Department of Mechanical Engineering, University of Alabama, Tuscaloosa, AL 35487, USA |
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Abstract: | Transitional jet diffusion flames provide the link between dynamics of laminar and turbulent flames. In this study, instabilities
and their interaction with the flow structure are explored in a transitional jet diffusion flame, with focus on isolating
buoyancy effects. Experiments are conducted in hydrogen flames with fuel jet Reynolds number of up to 2,200 and average jet
velocity of up to 54 m/s. Since the fuel jet is laminar at the injector exit, the transition from laminar to turbulent flame
occurs by the hydrodynamic instabilities in the shear layer of fuel jet. The instabilities and the flow structures are visualized
and quantified by the rainbow schlieren deflectometry technique coupled with a high-speed imaging system. The schlieren images
acquired at 2,000 frames per second allowed exposure time of 23 μs with spatial resolution of 0.4 mm. Results identify a hitherto
unknown secondary instability in the flame surface, provide explanation for the observed intermittency in the breakpoint length,
show coherent vortical structures downstream of the flame breakpoint, and illustrate gradual breakdown of coherent structures
into small-scale random structures in the far field turbulent region. |
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Keywords: | Diffusion flame instabilities Flame flicker Transition in flames Rainbow schlieren deflectometry |
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