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Vortical structure in the wake of a transverse jet

Fric, T. F. and Roshko, A. (1994) Vortical structure in the wake of a transverse jet. Journal of Fluid Mechanics, 1994 . pp. 1-47. ISSN 0022-1120.

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Structural features resulting from the interaction of a turbulent jet issuing transversely into a uniform stream are described with the help of flow visualization and hot-wire anemometry. Jet-to-crossflow velocity ratios from 2 to 10 were investigated at crossflow Reynolds numbers from 3800 to 11400. In particular, the origin and formation of the vortices in the wake are described and shown to be fundamentally different from the well-known phenomenon of vortex shedding from solid bluff bodies. The flow around a transverse jet does not separate from the jet and does not shed vorticity into the wake. Instead, the wake vortices have their origins in the laminar boundary layer of the wall from which the jet issues. It is argued that the closed flow around the jet imposes an adverse pressure gradient on the wall, on the downstream lateral sides of the jet, provoking 'separation events’ in the wall boundary layer on each side. These result in eruptions of boundary-layer fluid and formation of wake vortices that are convected downstream. The measured wake Strouhal frequencies, which depend on the jet-crossflow velocity ratio, match the measured frequencies of the separation events. The wake structure is most orderly and the corresponding wake Strouhal number (0.13) is most sharply defined for velocity ratios near the value 4. Measured wake profiles show deficits of both momentum and total pressure.

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Additional Information:Copyright © 1994 Cambridge University Press. Reprinted with permission. (Received 19 August 1993 and in revised form 10 June 1994) This work benefited from earlier, exploratory experiments by D. Kuzo; from discussions with him, J.E. Broadwell and H. Hornung; and from the collaborative experiment in soap-film flow with M. Gharib. It was supported by the Office of Naval Research under contract NOOO14-85-K-0646 and grant N00014-89-5-1991.
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Deposited On:14 Apr 2008
Last Modified:03 Oct 2019 00:06

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