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Organized motions in a fully developed turbulent axisymmetric jet

Published online by Cambridge University Press:  26 April 2006

Jin Tso  and
Fazle Hussain
Jin Tso
Affiliation:
Department of Mechanical Engineering, University of Houston, TX 77004, USA Present address: Aeronautical Engineering Department, California Polytechnic State University, San Luis Obispo, CA 93407, USA.
Fazle Hussain
Affiliation:
Department of Mechanical Engineering, University of Houston, TX 77004, USA
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Abstract

An experiment has been conducted to study the occurrence, configuration and dynamics of large-scale coherent vortical motions in the fully developed region of a turbulent axisymmetric jet. The key idea is to use vorticity signals from a spatial grid to detect and sample large-scale vortical structures and then use the (smoothed) vorticity peaks of spatial vorticity patterns to align and ensemble average successive realizations to determine structure configuration and dynamics. Measurements were made in an air jet at ReD = 69000 by employing a radial rake of seven × -wires to obtain the azimuthal vorticity map. Two additional conditioning probes were placed ± 90° away from the rake to determine the three-dimensional phase and hence the structure configuration. Structures with axisymmetric, helical and double helical configurations have been educed. Among them, the helical structures are far more dominant than the others, and the jet dynamics are thus discussed in terms of these helical structures. Helical structures move radially outward as they advect downstream. This radial movement, in conjunction with simultaneous local ejection of turbulent fluid and subsequent entrainment of the ejected fluid with ambient fluid, appears to be a major means of jet spreading. The shear strain rate is strong on the downstream side of the structure, causing intense small-scale turbulence production and mixing there.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 203 , June 1989 , pp. 425 - 448
Copyright
© 1989 Cambridge University Press

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