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Transverse jet mixing characteristics

Published online by Cambridge University Press:  02 February 2016

L. Gevorkyan ,
T. Shoji ,
D. R. Getsinger ,
O. I. Smith  and
A. R. Karagozian
L. Gevorkyan
Affiliation:
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA 90095-1597, USA
T. Shoji
Affiliation:
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA 90095-1597, USA
D. R. Getsinger
Affiliation:
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA 90095-1597, USA
O. I. Smith
Affiliation:
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA 90095-1597, USA
A. R. Karagozian*
Affiliation:
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA 90095-1597, USA
*
†Email address for correspondence: [email protected]
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Abstract

This experimental study explores and quantifies mixing characteristics associated with a gaseous round jet injected perpendicularly into cross-flow for a range of flow and injection conditions. The study utilizes acetone planar laser-induced fluorescence imaging to determine mixing metrics in both centreplane and cross-sectional planes of the jet, for a range of jet-to-cross-flow momentum flux ratios ($2\leqslant J\leqslant 41$), density ratios ($0.35\leqslant S\leqslant 1.0$) and injector configurations (flush nozzle, flush pipe and elevated nozzle), all at a fixed jet Reynolds number of 1900. For the majority of conditions explored, there is a direct correspondence between the nature of the jet’s upstream shear layer instabilities and structure, as documented in detail in Getsinger et al. (J. Fluid Mech., vol. 760, 2014, pp. 342–367), and the jet’s mixing characteristics, consistent with diffusion-dominated processes, but with a few notable exceptions. When quantified as a function of distance along the jet trajectory, mixing metrics for jets in cross-flow with an absolutely unstable upstream shear layer and relatively symmetric counter-rotating vortex pair cross-sectional structure tend to show better local molecular mixing than for jets with convectively unstable upstream shear layers and generally asymmetric cross-sectional structures. Yet the spatial evolution of mixing with downstream distance can be greater for a few specific convectively unstable conditions, apparently associated with the initiation and nature of shear layer rollup as a trigger for improved mixing. A notable exception to these trends concerns conditions where the equidensity jet in cross-flow has an upstream shear layer that is already absolutely unstable, and the jet density is then reduced in comparison with that of the cross-flow. Here, density ratios below unity tend to mix less well than for equidensity conditions, demonstrated to result from differences in the nature of higher-density cross-flow entrainment into lower-density shear layer vortices.

JFM classification

Instability: Absolute/convective instability Wakes/Jets: Jets Mixing: Mixing
Type
Papers
Information
Journal of Fluid Mechanics , Volume 790 , 10 March 2016 , pp. 237 - 274
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Copyright
© 2016 Cambridge University Press 

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