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Turbulent mixing at a stable density interface : the variation of the buoyancy flux–gradient relation
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Guyez, Estelle Marie Chantal, Flor, J. -B. and Hopfinger, E. J. (2007) Turbulent mixing at a stable density interface : the variation of the buoyancy flux–gradient relation. Journal of Fluid Mechanics, Vol.57 . pp. 127-136. doi:10.1017/S0022112007004958 ISSN 0022-1120.
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Official URL: http://dx.doi.org/10.1017/S0022112007004958
Abstract
Experiments conducted on mixing across a stable density interface in a turbulent Taylor–Couette flow show, for the first time, experimental evidence of an increase in mixing efficiency at large Richardson numbers. With increasing buoyancy gradient the buoyancy flux first passes a maximum, then decreases and at large values of the buoyancy gradient the flux increases again. Thus, the curve of buoyancy flux versus buoyancy gradient tends to be N-shaped (rather than simply bell shaped), a behaviour suggested by the model of Balmforth et al. (J. Fluid Mech. vol. 428, 1998, p. 349). The increase in mixing efficiency at large Richardson numbers is attributed to a scale separation of the eddies active in mixing at the interface; when the buoyancy gradient is large mean kinetic energy is injected at scales much smaller than the eddy size fixed by the gap width, thus decreasing the eddy turnover time. Observations show that there is no noticeable change in interface thickness when the mixing efficiency increases; it is the mixing mechanism that changes. The curves of buoyancy flux versus buoyancy gradient also show a large variability for identical experimental conditions. These variations occur at time scales one to two orders of magnitude larger than the eddy turnover time scale.
| Item Type: | Journal Article | ||||
|---|---|---|---|---|---|
| Subjects: | Q Science > QA Mathematics | ||||
| Divisions: | Faculty of Science, Engineering and Medicine > Engineering > Engineering | ||||
| Library of Congress Subject Headings (LCSH): | Turbulence, Mixing, Laminar flow, Fluid dynamics | ||||
| Journal or Publication Title: | Journal of Fluid Mechanics | ||||
| Publisher: | Cambridge University Press | ||||
| ISSN: | 0022-1120 | ||||
| Official Date: | 19 April 2007 | ||||
| Dates: |
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| Volume: | Vol.57 | ||||
| Page Range: | pp. 127-136 | ||||
| DOI: | 10.1017/S0022112007004958 | ||||
| Status: | Peer Reviewed | ||||
| Access rights to Published version: | Open Access (Creative Commons) | ||||
| Funder: | France. Service hydrographique et océanographique de la marine (SHOM), France. Délégation générale pour l'armement (DGA) |
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