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Three-dimensional-mode resonance in far wakes

Published online by Cambridge University Press:  26 April 2006

T. C. Corke
Affiliation:
Illinois Institute of Technology, Fluid Dynamics Research Center, Mechanical and Aerospace Engineering Department, Chicago, IL 60616, USA
J. D. Krull
Affiliation:
Illinois Institute of Technology, Fluid Dynamics Research Center, Mechanical and Aerospace Engineering Department, Chicago, IL 60616, USA
M. Ghassemi
Affiliation:
Illinois Institute of Technology, Fluid Dynamics Research Center, Mechanical and Aerospace Engineering Department, Chicago, IL 60616, USA

Abstract

This work is aimed at understanding mechanisms which govern the growth of secondary three-dimensional modes of a particular type which feed from a resonant energy exchange with the primary Kármán instability in two-dimensional wakes. Our approach was to introduce controlled time-periodic three-dimensional (oblique) wave pairs of equal but opposite sign, simultaneously with a two-dimensional wave. The waves were introduced by an array of v-component-producing elements on the top and bottom surfaces of the body. These were formed by metallized electrodes which were vapour deposited onto a piezoelectrically active polymer wrapped around the surface. The amplitudes, streamwise and spanwise wavenumbers, and initial phase difference are all individually controllable. The initial work focused on a fundamental/subharmonic interaction, and the dependence on spanwise wave-number. The results include mode eigenfunction modulus and phase distributions in space, and stream functions for the phase-reconstructed flow field. Analysis of these shows that such a resonance mechanism exists and its features can account for characteristic changes associated with the growth of three-dimensional structures in the wake of two-dimensional bodies.

Type
Research Article
Copyright
© 1992 Cambridge University Press

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