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Large-scale structure in the far field of buoyant jets

Papantoniou, Dimitris and List, E. John (1989) Large-scale structure in the far field of buoyant jets. Journal of Fluid Mechanics, 209 . pp. 151-190. ISSN 0022-1120. doi:10.1017/S002211208900306X.

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The flow structure and entrainment mechanisms in the far field of a round vertical buoyant jet have been studied experimentally by use of an optical technique based on laser-induced fluorescence (LIF). A large number of essentially instantaneous tracer concentration profiles were recorded for each experimental run by combining LIF with linear photodiode array imaging and high-speed digital data acquisition. Analysis of the resulting high-resolution flow images indicates that the far-field region is dominated by the periodic passage of structures spanning the entire radial flow extent. Ambient fluid is entrained by vortical motions and is transported to regions deep into the flow interior. Correlation analysis discloses that the passage frequency of the structures scales with the local mean velocity and flow width. Conditional averaging of the data indicates that the downstream frontal region of the structure is well mixed and at higher concentration level than the back and side regions where ambient fluid is intermittently present. This results in an axial concentration gradient within the structure, analogous to the ramp-like pattern previously observed in heated air jets. In comparison to the momentum-driven flow the ambient fluid presence in the flow interior is greatly increased when body forces are the driving mechanism. This appears to result from the influence of buoyancy forces in the production of turbulent vortices at the integral scale. An important feature of both the momentum-driven and buoyancy-driven flows investigated is the strongly intermittent character of the concentration field. This raises the issue of the appropriateness of gradient-diffusion theories for the description of such flows.

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Additional Information:© 1989 Cambridge University Press. (Received 23 August 1988 and in revised form 10 February 1989) The authors express their appreciation for the support of colleagues : Professors Donald Coles, Edward Zukoski, Paul Dimotakis and Manooch Koochesfahani, who all contributed to the initiation and evolution of this work in a variety of ways. The financial support of the National Science Foundation, through Grants No. CEE81-17272 AO1 and MSM84-12641 AO1, and the Alexander Onassis Foundation (to D. P.) are gratefully acknowledged.
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NSFCEE81-17272 A01
NSFMSM84-12641 A01
Alexander S. Onassis Public Benefit FoundationUNSPECIFIED
Record Number:CaltechAUTHORS:20160418-152805105
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Official Citation:Dimitris Papantoniou and E. John List (1989). Large-scale structure in the far field of byoyant jets. Journal of Fluid Mechanics, 209, pp 151-190 doi:10.1017/S002211208900306X
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:66259
Deposited By: George Porter
Deposited On:18 Apr 2016 22:35
Last Modified:10 Nov 2021 23:55

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