Poster: The evolving morphology of negatively-buoyant vortex rings

When buoyant vortex rings form, azimuthal disturbances occur on their surface. When the magnitude of the disturbance is sufficiently high, the ring will become turbulent. This paper establishes conditions for categorization of a buoyant vortex ring as laminar, transitional, or turbulent. The transition regime of enclosed-air buoyant vortex rings rising in still water was examined experimentally via two high-speed cameras. Sequences of the recorded pictures were analyzed using matlab. Key observations were summarized as follows: for Reynolds number lower than 14,000, Bond number below 30, and Weber number below 50, the vortex ring could not be produced. A transition regime was observed for Reynolds numbers between 40,000 and 70,000, Bond numbers between 120 and 280, and Weber number between 400 and 800. Below this range, only laminar vortex rings were observed, and above, only turbulent vortex rings.

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Experimental study of buoyant vortex rings

Journal of Applied Mechanics and Technical Physics ◽

10.1007/bf00914471 ◽

1983 ◽

Vol 24 (1) ◽

pp. 16-21 ◽

Cited By ~ 4

Author(s):

B. I. Zaslavskii ◽

I. M. Sotnikov

Keyword(s):

Experimental Study ◽

Vortex Rings ◽

Buoyant Vortex Rings

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Drag of buoyant vortex rings

Physical Review E ◽

10.1103/physreve.92.043024 ◽

2015 ◽

Vol 92 (4) ◽

Author(s):

Ahmadreza Vasel-Be-Hagh ◽

Rupp Carriveau ◽

David S.-K. Ting ◽

John Stewart Turner

Keyword(s):

Vortex Rings ◽

Buoyant Vortex Rings

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Turbulent Effects in the Formation of Buoyant Vortex Rings

Journal of Applied Physics ◽

10.1063/1.1709085 ◽

1967 ◽

Vol 38 (10) ◽

pp. 4097-4098 ◽

Cited By ~ 7

Author(s):

Timothy Fohl

Keyword(s):

Vortex Rings ◽

Buoyant Vortex Rings

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A comparison between buoyant vortex rings and vortex pairs

Journal of Fluid Mechanics ◽

10.1017/s0022112060000189 ◽

1960 ◽

Vol 7 (3) ◽

pp. 419-432 ◽

Cited By ~ 53

Author(s):

J. S. Turner

Keyword(s):

Linear Density ◽

Considerable Increase ◽

Final Height ◽

Two Dimensions ◽

Vortex Rings ◽

Maximum Height ◽

Finite Radius ◽

Effective Height ◽

Vortex Pairs ◽

Buoyant Vortex Rings

In this paper it is shown how earlier results for buoyant vortex rings may be extended to describe the corresponding two-dimensional case, which arises in the theory of bent-over plumes. It is again assumed that in uniform surroundings the circulation remains constant while the buoyancy acts to increase the momentum of the pair. The behaviour in two dimensions is quite different from that in three, however; a buoyant vortex ring spreads linearly with height, whereas a buoyant pair spreads exponentially with height, or linearly with time (and therefore, in a bent-over plume, linearly with distance downwind).The theory has been extended to describe the rise of buoyant rings and pairs through stably stratified surroundings having a linear density gradient. The behaviour near the maximum height reached is found to depend critically in both cases on the relative rates at which the circulation and the momentum fall to zero. If these reach zero together, the rings or pairs will steadily increase in size and come to rest at a finite height and with a finite radius. If the circulation is non-zero when the momentum vanishes, the radius begins to decrease soon after the buoyancy becomes zero, and the vortices will therefore tend to break up suddenly and mix into their surroundings. There is a considerable increase in the final height which should be attained by vortex rings or bentover plumes if the initial circulation is increased; it is suggested that releasing smoke intermittently, rather than continuously, at high velocity might be a means of increasing the effective height of chimneys in calm conditions. When the circulation reaches zero before the momentum does, the solutions indicate that the radius becomes very large near the level of zero buoyancy.

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Formation regimes of vortex rings in negatively buoyant starting jets

Journal of Fluid Mechanics ◽

10.1017/jfm.2012.554 ◽

2013 ◽

Vol 716 ◽

pp. 470-486 ◽

Cited By ~ 7

Author(s):

C. Marugán-Cruz ◽

J. Rodríguez-Rodríguez ◽

C. Martínez-Bazán

Keyword(s):

Vortex Ring ◽

Richardson Number ◽

Vortex Formation ◽

Vortex Rings ◽

Vortex Identification ◽

Buoyant Flows ◽

Formation Number ◽

Secondary Vortices ◽

Starting Jet ◽

Negatively Buoyant

AbstractThe formation of vortex rings in negatively buoyant starting jets has been studied numerically for different values of the Richardson number, $\mathit{Ri}$, covering the range of weak to moderate buoyancy effects ($0\leq \mathit{Ri}\leq 0. 20$). Two different regimes have been identified in the vortex formation and the transition between them takes place at $\mathit{Ri}\approx 0. 03$. The vorticity distribution inside the vortex ring after pinching off from the trailing stem as well as the total amount of circulation it encloses (characterized by the formation number, $F$) show different behaviours with the Richardson number in the two regimes. The differences are associated with the different mechanisms by which the head vortex absorbs the circulation injected by the starting jet. While secondary vortices are engulfed by the leading vortex before separating from the trailing jet in the weak buoyancy effects regime ($0\lt \mathit{Ri}\lt 0. 03$), this phenomenon is not observed in the moderate buoyancy effects regime ($0. 03\lt \mathit{Ri}\lt 0. 2$). Moreover it is shown that the formation number of a negatively buoyant vortex ring can be determined by considering that its dynamics are similar to that of a neutrally buoyant vortex but propagating with velocity corresponding to the negatively buoyant one. Based on this simple idea, a phenomenological model is presented to describe quantitatively the evolution of the formation number with the Richardson number, $F(\mathit{Ri})$, obtained numerically. In addition, the limitations of different vortex identification methods used to evaluate the vortex properties in buoyant flows are discussed.

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A balloon bursting underwater

Journal of Fluid Mechanics ◽

10.1017/jfm.2015.126 ◽

2015 ◽

Vol 769 ◽

pp. 522-540 ◽

Cited By ~ 5

Author(s):

A. R. Vasel-Be-Hagh ◽

R. Carriveau ◽

D. S.-K. Ting

Keyword(s):

Surface Tension ◽

Vortex Ring ◽

Buoyancy Force ◽

Reasonable Agreement ◽

Ring Expansion ◽

Vortex Rings ◽

Rise Velocity ◽

Modified Model ◽

The Stability ◽

Buoyant Vortex Rings

A buoyant vortex ring produced by an underwater bursting balloon was studied experimentally. The effect of dimensionless surface tension on characteristics including rise velocity, rate of expansion, circulation, trajectory, and lifetime of the vortex ring bubble was investigated. Results showed reasonable agreement with the literature on vortex rings produced by conventional approaches. It was observed that as the dimensionless surface tension increased, the rise velocity, the circulation and consequently the stability of the vortex ring bubble increased; however, the rate of expansion tends toward constant values. A semi-analytical model is proposed by modifying the drag-based model presented by Sullivan et al. (J. Fluid Mech., vol. 609, 2008, pp. 319–347) to make it applicable to buoyant vortex rings. The modified model suggests that the vortex ring expansion is essentially due to the buoyancy force. An expression is also derived for the circulation in terms of the initial volume of the balloon and the depth at which the balloon bursts.

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