secondary instability and three-dimensionalization in a laboratory accelerating shear layer with varying density differences开题资料.pdf

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Oratmospneres
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ELSEVIER Dynamics of Atmospheres and Oceans 23 (1996) 125-138
Secondary instability and three-dimensionalization
in a laboratory accelerating shear layer
with varying density differences
. Caulfield a,*, S. Yoshida b, . Peltier a
a Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ont. M5S 1,47, Canada
b Department of Engineering Science, Hokkaido University, North 13 West 8, Sapporo 060, Japan
Received 1 July 1994; revised 14 February 1995; accepted 6 March 1995
Abstract
We investigate the processes by which an accelerating stratified shear flow undergoes the
transition to turbulence in a sequence of experiments in a tilted tank. We observe that the
processes by which the flow undergoes breakdown are both complex and diverse, and
suggest that the ratio, D, of the depth of the shear layer to the total tank depth and/or the
(nondimensional) total density difference are important parameters in the determination of
the dominant structures. In general, inherently three-dimensional, and relatively large-scale,
flow structures strongly suppress simple subharmonic vortex pairing, and appear to domi-
nate totally the transition to turbulence. In certain circumstances, the primary instabilities
of the flow, namely Kelvin-Helmholtz billows, are able to develop in a quasi-two-dimen-
sional manner before interaction between neighbouring billows becomes significant. In
these circumstances, narrow secondary streamwise 'tubes' of vorticity are observed between
neighbouring billows. Alternatively subharmonic, quasi-two-dimensional vortex mergings