Why doesn't a ring vortex immediately float to the surface?

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    Mechanics Ring Vortex
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Discussion Overview

The discussion centers on the behavior of a ring vortex created by dolphins and why it does not immediately float to the surface, contrasting it with the behavior of falling objects like golf balls. Participants explore the dynamics of buoyancy, flow, and the effects of surrounding water movement.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that the ring vortex does not float to the surface immediately and questions the underlying reasons for this behavior.
  • Another participant compares the behavior of bubbles in water to golf balls in free fall, suggesting that the dynamics are inherently different.
  • A participant explains that the air pockets do not accelerate upwards at the same rate as a falling ball due to the influence of water flow.
  • It is proposed that the movement of the air pocket is influenced by the flow of water modified by the dolphins, affecting the buoyant force.
  • One participant expresses skepticism about the presence of modifying flow in the case of the water vortex, referencing a video of a smoke ring that appears to lack such flow.
  • A response clarifies that the vortex creates a circular flow, which differs from still water conditions, impacting how bubbles behave.
  • Another participant interprets a previous comment as suggesting an underwater current that counteracts the vortex's natural tendency to rise.

Areas of Agreement / Disagreement

Participants express differing views on the influence of water flow on the behavior of the ring vortex, indicating that multiple competing explanations exist without a consensus on the primary factors at play.

Contextual Notes

Participants discuss the complexities of buoyancy and flow dynamics, highlighting the need for further exploration of how these factors interact in different scenarios. There are unresolved questions regarding the specific effects of water movement on the ring vortex.

Nickelodeon
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If you look at this YouTube video you will see an example of a ring vortex made by a dolphin (there are quite a few other examples). The problem is I can't understand why the ring doesn't immediately float to the surface. Only when it breaks up do the bubbles rise. The ring appears to counteract expected behaviour. Can anyone explain this?
thanks
Nick
 
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If you stand 50m from the tee at a Golf Major, you will notice that the balls that have just been hit do not immediately fall to the ground - they actually "come down" perhaps 280 yards from the tee (230 yards from you).
Why should these bubbles behave so differently to the balls.
They do behave somewhat differently, in that they don't travel 200+ yards before heading for the surface.
 
PeterO said:
Why should these bubbles behave so differently to the balls.
Because it's a different situation. A ball in free fall accelerates at 1g downwards, regardless of it's horizontal movement. Those air pockets are not always accelerating upwards at the same rate.
 
Last edited:
Nickelodeon said:
The problem is I can't understand why the ring doesn't immediately float to the surface.
The movement of the air pocket is dominated by the flow of the water, which is being modified by the dolphins. The inertia and angular momentum of the water are modulating the effect of the buoyant force.
 
I also thought it may be dominated by a modified flow of water produced during the ring's creation but then if you look at this air vortex cannon video, about 1m 40 secs in, and look at the residual smoke there doesn't appear to be any modifying air flow associated with the smoke ring. I would suspect, in the case of the water scenario, there will be no modifying flow.
 
Nickelodeon said:
there doesn't appear to be any modifying air flow associated with the smoke ring
What do you mean by that? The vortex constitutes a circular flow.

When an air bubble raises in still water, the water above the bubble flows below the bubble due to unbalanced gravity. But the water around that air ring is circulating fast, with pressure gradients different from still water.
 
I thought that your comment, "The movement of the air pocket is dominated by the flow of the water, which is being modified by the dolphins." inferred that there was a movement of water (underwater current) along the direction of the forward motion of the ring which was somehow counteracting the natural tendency for the vortex "bubble" to rise.
 

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