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Influence of wave dispersion on vortex pairing in a jet

Published online by Cambridge University Press:  19 April 2006

R. A. Petersen
R. A. Petersen
Affiliation:
Department of Aerospace Engineering, University of Southern California, Los Angeles
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Abstract

The geometry of large-scale structures in the turbulent mixing layer of a moderate Reynolds number jet is deduced from measurements of the fluctuating pressure in the hydrodynamic near field. The structures are rings of concentrated vorticity that distort with downstream distance until statistical axisymmetry disappears. The rings are spaced quasi-periodically and coalesce with each other, producing larger spacings. Statistical and flow-visualization techniques are applied to free and forced jets over a range of Reynolds numbers from 5000 to 50000 to demonstrate that rings of a given spacing do not coalesce with each other until they are far enough downstream that the local mixing layer has attained some critical thickness which scales with the wavelength of the vortex pair. Wave dispersion is evaluated as a plausible mechanism for localizing the coalescences. The central feature of the model is the observation that a shear layer is dispersive to wavelengths much longer than its thickness and non-dispersive to shorter waves.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 89 , Issue 3 , 13 December 1978 , pp. 469 - 495
Copyright
© 1978 Cambridge University Press

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