Underwater Bubble Rings

Same thing as smoke rings, just under water.... the ring spins...

I understand that it happens,my question is what holds it together and slows it's ascent.The same quantity of air in a single bubble would rise very quickly,but this appears to be almost neutral in buoyancy.The spin speed is apparently limited to a certain range before it loses cohesion.There is also more drag on the inside of the toroid than on the outside,and a differential in friction across the whole surface.Lot of tricky physics going on here,as well as being mesmerizing.A PhD thesis could be written on the forces and dynamics involved.

I am thinking surface tension of the water at the interface,pressure of the water and ,centrifugal force are all in a stable balance until one of the forces becomes dominant and the cohesion disappears.

If the bubble spins to fast or becomes too large,it loses integrity.

In a regular bubble,the inside and outside pressure is balanced and the bubble increases in size as it rises,and one can see the effect of friction on the shape of the bubble.Somehow,the rings are not very buoyant,and very slowly begin to rise.

Perhaps there is a gyro effect going on also due to the rotation,especially if the internal air is also rotating at a different angle than the ring as a whole.Perhaps the internal air is rotating at a 90 degree angle to the ring is also assisting in keeping the toroid open.Imagine a spring coiled into a toroid,but with all of the turns rotating and separated by molecular distances,and imagine the whole toroid rotating.

Plenty of questions for the inquiring mind.

If only porpoises could speak English,or we could speak their language.

Well I think that precession comes into play as a stabilizing force as well....it's like having a thousand gyroscopes tied together....

Toroidal vortex generator....

That bubble looks like a slow motion playback of a rubber band release.

Very interesting gif...Notice how the rings seem to be attracted when the edge of the small ring passes over the edge of large ring? Sort of like when a parachutist "steals the air" from the one above him.

rse.

Those particular rings are being directed and stabilized by dolphins.

That is what my 5 year old grandson said.It took him about 5 seconds to answer.

My guess is that it's centrifugal force that keeps the air inside the vortex.

For example, if you have a helium balloon in your car and you turn a corner, the balloon is lighter than the air in the car and it will go to the inside of the turn. The air is lighter than the water in the spinning vortex, so it moves toward the axis of the vortex.

The buoyancy of the air trapped inside is small compared to the mass of water involved in the ring vortex and to rise, it would have to drag the entire vortex with it.

https://en.wikipedia.org/wiki/Vortex_ring

That is exactly what I attempted to describe with the spring coil analogy,but I could not find an image of it.I learned a new word today:poloidal.Thanks!

I wonder how one would describe the motion if the toroid was mounted in a double gimbal with each gimbal axis rotating at 90 degree angles to each other,at various angles in relation to the toroid.

I'm getting a headache,must need more caffeine..or ethanol.

Thanks! That's a new word to me as well!

Notice how the arrows seem to reverse direction if you look at them long enough?

Rixter, does it move, because ? the pressure on the inside is different than the pressure on the outside ?

When it moves, does the mass expand and cause forward momentum to reduce ?

Tony

The closest analogy I can think of is a hurricane or tornado.The pressure in the center is actually less than the pressure outside,but the centrifugal force prevents the collapse.Obviously they have different starting conditions,but if you could hook both ends of a tornado together you would have something similar.

I think I understand your question...

The bubble ring is just a ring vortex with air trapped at its core. To generate a ring vortex, you have a "blob" of fluid ejected into a stationary fluid. Where it meets the stationary fluid, the fluid rolls around and the moving "blob" is essentially "rolling on wheels" with very little loss of momentum. The ring follows the moving blob. I'm thinking the forward motion of the ring is just the original momentum of the "blob".

"Unlike a sea wave, whose motion is only apparent, a moving vortex ring actually carries the spinning fluid along. Just as a rotating wheel lessens friction between a car and the ground, the poloidal flow of the vortex lessens the friction between the core and the surrounding stationary fluid, allowing it to travel a long distance with relatively little loss of mass and kinetic energy, and little change in size or shape. Thus, a vortex ring can carry mass much further and with less dispersion than a jet of fluid. That explains, for instance, why a smoke ring keeps traveling long after any extra smoke blown out with it has stopped and dispersed.^{[3] "}

https://en.wikipedia.org/wiki/Vortex_ring

What would happen if you could construct a solid object in a toroid shape and circulated mercury at high velocity in a poloid direction inside the toroid?Is mercury diamagnetic?Just curious.

'Is mercury diamagnetic?'.

.

Yes, weakly so at reasonable temperatures, on the order of twice as diamagnetic as aluminum on a molar basis. At less reasonable temperatures, i.e. below 4 Kelvin, mercury is a perfect diamagnet as it is a superconductor....so long as the temperature is low enough for the applied field. However, mercury turns to a solid at much high temperatures than that.

'What will happen?'.

The mercury will increase in temperature slightly as it slows. The five year old in your vicinity may have already informed you of this. If so,, he is correct, again.

He is the one that posed the question via his grandpa.He said he figured that, and thanks for confirming.!

He wants to know if it will generate a magnetic field,similar to the Earth's core of circulating molten metal.

I doubt a measurable magnetic field would be developed attributable to the experiment as described.

It would probably need some mechanism to introduce and maintain some charge separation allowing relative motion of the separate charges.

In the liquid core of the Earth, this might involve isotopes that decay via alpha or beta processes while traversing gradients of temperature, pressure, gravitational potential, and/or (dynamically) magnetic field strength.. Such processes might be able to develop a magnetic field or alternately some initial jumpstart might have been needed. Perhaps early on a magnetar wizzed by Earth and rang in the magnetism that bas been resonating complexly with core reversals every 10,000 years or so.

Smart kid

Electrical transformers are cylindrical in shape and one exploded in Chicago generating a smoke ring in the sky...

https://www.youtube.com/watch?v=0WRa0sjWX58

Now if it turned into a smiley face that would be really amazing!

Unfortunately, a smiley face is not a solution to Navier-Stokes equations...

Viewed from the side it could look like a UFO.

The spinning torus is actually in the water, not the air ring. The air is trapped at the spinning center of the water torus and makes it visible. The centrifugal force of the spinning water creates the low pressure ring that holds the air. The motion and behavior of the air ring reflect the action of the water torus.