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On the periodically excited plane turbulent mixing layer, emanatingfrom a jagged partition

Published online by Cambridge University Press:  08 October 2007

E. KIT ,
I. WYGNANSKI ,
D. FRIEDMAN ,
O. KRIVONOSOVA  and
D. ZHILENKO
E. KIT
Affiliation:
Department of Fluid Mechanics and Heat Transfer, Faculty of Engineering Tel-Aviv University, Tel-Aviv 69978, Israel kit@eng.tau.ac.il
I. WYGNANSKI
Affiliation:
Department of Fluid Mechanics and Heat Transfer, Faculty of Engineering Tel-Aviv University, Tel-Aviv 69978, Israel kit@eng.tau.ac.il
D. FRIEDMAN
Affiliation:
Department of Fluid Mechanics and Heat Transfer, Faculty of Engineering Tel-Aviv University, Tel-Aviv 69978, Israel kit@eng.tau.ac.il
O. KRIVONOSOVA
Affiliation:
Institute of Mechanics, Moscow State University, Michurinski pr., 1, Moscow, Russia
D. ZHILENKO
Affiliation:
Institute of Mechanics, Moscow State University, Michurinski pr., 1, Moscow, Russia
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Abstract

The flow in a turbulent mixing layer resulting from two parallel differentvelocity streams, that were brought together downstream of a jagged partitionwas investigated experimentally. The trailing edge of the partition had a shorttriangular ‘chevron’ shape that could also oscillate upand down at a prescribed frequency, because it was hinged to the stationary partof the partition to form a flap (fliperon). The results obtained from thisexcitation were compared to the traditional results obtained by oscillating atwo-dimensional fliperon. Detailed measurements of the mean flow and thecoherent structures, in the periodically excited and spatially developing mixinglayer, and its random constituents were carried out using hot-wire anemometryand stereo particle image velocimetry.

The prescribed spanwise wavelength of the chevron trailing edge generatedcoherent streamwise vortices while the periodic oscillation of this fliperonlocked in-phase the large spanwise Kelvin–Helmholtz (K-H) rolls,therefore enabling the study of the inter- action between the two. Thetwo-dimensional periodic excitation increases the strength of the spanwise rollsby increasing their size and their circulation, which depends on the inputamplitude and frequency. The streamwise vortices generated by the jaggedtrailing edge distort and bend the primary K-H rolls. The present investigationendeavours to study the distortions of each mode as a consequence of theirmutual interaction. Even the mean flow provides evidence for the local bulgingof the large spanwise rolls because the integral width (the momentum thickness,θ), undulates along the span. The lateral location of the centre ofthe ensuing mixing layer (the location where the mean velocity is the arithmeticaverage of the two streams, y0),also suggests that these vortices are bent. Phase-locked and ensemble-averagedmeasurements provide more detailed information about the bending and bulging ofthe large eddies that ensue downstream of the oscillating chevron fliperon. Theexperiments were carried out at low speeds, but at sufficiently high Reynoldsnumber to ensure naturally turbulent flow.

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Type
Papers
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Journal of Fluid Mechanics , Volume 589 , 25 October 2007 , pp. 479 - 507
Copyright
Copyright © Cambridge University Press 2007

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