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The growth of large scales at defect sites in the plane mixing layer

Published online by Cambridge University Press:  26 April 2006

T. Dallard  and
F. K. Browand
T. Dallard
Affiliation:
Department of Aerospace Engineering. University of Southern California, Los Angeles. CA 90089–1191, USA
F. K. Browand
Affiliation:
Department of Aerospace Engineering. University of Southern California, Los Angeles. CA 90089–1191, USA
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Abstract

The evolution of vortex structure in the vicinity of a pattern defect or dislocation, generated experimentally by forcing a high Reynolds number mixing layer, is studied using a new two-dimensional wavelet transform called Arc. This transform localizes spectral information in physical space – as all wavelets do – but is not direction-specific in wavenumber space. Various types of forcing, including forcing at the fundamental and subharmonic wavenumbers, produce a range of mixing-layer responses. The most significant finding is that a dislocation site acts as a nucleus and initiates a rapid, localized evolution to larger scales. The area of the localized ‘patch’ grows approximately as the square of downstream distance. Defect-initiated patches bear generic similarities to the disturbed regions in cylinder wakes – commented upon recently by many researchers – and in particular to the Λ-structures described by Williamson (1992).

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 247 , February 1993 , pp. 339 - 368
Copyright
© 1993 Cambridge University Press

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