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On the transition from finite-volume negatively buoyant releases to continuous fountains

Myrtroeen, OJ and Hunt, GR (2012) On the transition from finite-volume negatively buoyant releases to continuous fountains. Journal of Fluid Mechanics, 698. pp. 168-184. ISSN 0022-1120

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Abstract

An experimental investigation to identify the source conditions that distinguish finite-volume negatively buoyant fluid projectile behaviour from fountain behaviour in quiescent environments of uniform density is described. Finite-volume releases are governed by their source Froude number Fr D and the aspect ratio L/D of the release, where L denotes the length of the column of fluid dispensed vertically from the nozzle of diameter D. We establish the influence of L/D on the peak rise heights of a release formed by dispensing saline solution into fresh water for 0<Fr D<6 and 0<L/D<34. Within these ranges, we determine the source conditions for which a flow may be regarded, in terms of the initial rise height attained, as either finite-volume or continuous flux. The critical aspect ratio (L/D) f, for a given Fr D, which when exceeded no longer influenced release behaviour, led to the determination of Fr D, (L/D) f paired source conditions that give rise to solely Froude-number-dependent, i.e. fountain-like, behaviour. As such, we make the link between finite-volume releases and continuous fountains. The Fr D(L/D) f pairs led us directly to the classification of a Fr D, L/D space from which source conditions giving rise to either negatively buoyant projectiles or fountains may be readily identified. The variation of (L/D) f with Fr D corresponds closely to established fountain regimes of very weak, weak and forced fountains. Moreover, our results indicate that the formation or otherwise of a primary vortex, as fluid is ejected, has a profound influence on the length of the dispensed fluid column that is necessary to achieve rise heights equal to fountain rise heights. © 2012 Cambridge University Press.

Item Type: Article
Uncontrolled Keywords: plumes/thermals
Subjects: UNSPECIFIED
Divisions: Div A > Fluid Mechanics
Depositing User: Cron Job
Date Deposited: 07 Mar 2014 11:29
Last Modified: 08 Dec 2014 02:31
DOI: 10.1017/jfm.2012.74