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Structural and stability characteristics of jets in crossflow

Published online by Cambridge University Press:  07 November 2014

D. R. Getsinger
Affiliation:
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA 90095-1597, USA
L. Gevorkyan
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]

Abstract

This experimental study examines the relationship between transverse jet structural characteristics and the shear layer instabilities forming on the upstream side of the jet column. Jets composed of mixtures of helium and nitrogen were introduced perpendicularly into a low-speed wind tunnel using several alternative injectors: convergent circular nozzles mounted either flush with or elevated above the tunnel floor, and a flush-mounted circular pipe. Both non-intrusive optical diagnostics (planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV)) and intrusive probe-based (hot-wire anemometry) measurements were used to explore a range of jet-to-crossflow momentum flux ratios and density ratios for which previous studies have identified upstream shear layer transition from convective to absolute instability. Remarkable correspondences were identified between formation of the well-known counter-rotating vortex pair (CVP) associated with the jet cross-section and conditions producing strong upstream shear layer vorticity rollup, arising typically from absolute instability in the shear layer. In contrast, asymmetries in the jet mean cross-sectional shape and/or lack of a clear CVP were observed to correspond to weaker, convectively unstable jet shear layers.

Type
Papers
Copyright
© 2014 Cambridge University Press 

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