Dolphins’ little ‘bubble-bursting’ game is a nifty underwater feat of physics

A bottlenose

dolphin

(Tursiops

truncates)

blowing a series

of bubble rings

underwater.

Photo credit: Kenichi Aihara

A nearly-

spherical

bubble comes

out from the

blow-hole of a

dolphin

The higher pressure at the

bottom of the bubble

pushes the bubble's bottom

surface up faster than the

top surface rises creating a

trail of fluid jet

Fluid jet puncturing

the bubble

What do dolphins, us, and an

erupting volcanoes have in

common?Dolphins and humans may both be

mammals, but neither is a steam of hot lava and

gases. So, what is it? The answer is: all three can

make vortex rings.

A vortex ring is a phenomenon where

fluids or gases knot and spin in a closed,

usually circular loop around an imaginary

axis line. Tornado stability, volcanic

eruptions, mushroom clouds, as well as the

blood discharge going out of the left atrium

to the left ventricular cavity in the human

heart, revolves around the same physics of

vortex rings (Gharib, et al., 1998).

Image 2: Spark photography image of a vortex ring in flightImage 1: Smoke ring seen from Mount Etna, Italy

(through practice) from our mouth by

cigarette smoke – except that obviously it

would not be underwater. (A little note: All the

cool kids are doing it.) Meanwhile, the giant

volcano of Mount Etna, the tallest active

volcano in Europe, was also observed to be

forming large smoke rings measuring up to

50 meters in diameter (Tomlinson, 2014).

Its Role in Many Other Processes

Vortex Rings are Doughnut-Shaped Rings

As the bubble ring rises, the ring

expands due to decreasing

water pressure

Dolphins and other cetaceans such as

whales, and porpoises, are marine mammals that

have been observed making bubble rings with

their blowhole as their own little underwater

game. These bubble rings are scientifically

termed as ‘vortex rings’, and can too be made

Bursting the Bubble

Bubble ring is formed

2

Photo credit: Own illustration

Photo credit: Chris Weber

Photo credit: George Lucey Jr. & Dr. D. Lyon

Smoke Rings from Volcanoes

Direction of travel

Direction of rotation

By flicking the tip of their

dorsal fin, this dolphin

expels air from its

blowhole, forming a torus

or ring-like form of

bubble, causing a rapid

acceleration of a small

mass of water. These

toroidal vortices are

formed by the drag at

the outer edges of the

fast-flowing packet of

surrounding water,

slowing down the flow

relative to the center.

Vortex rings from a

volcano eruption is a rare

phenomenon. It requires:

1. A particular geometric

configuration of a circular vent

exit

2. Correct

velocity for

individual puff

of gas

expulsion

The round shape of the smoke

ring is formed because the air

that occupies the center of the

ring is forced out with a higher

velocity.

‘Formation of smoke

ring from volcanoes

are similar to how

smokers make smoke

rings with their

mouths - the volcano

has a deep crater pit

with circular vertical

walls like a chimney.’

CHRIS WEBER, Volcanologist

So far smoke rings has made its

appearance at two mountains:

1. Mt. Etna

2. Mt. Stromboli

3

Photo credit: PBS.org

Photo credit: Own illustration

Vortex Ring in a Non-Newtonian Viscoelastic FluidDespite having the same

value of Reynold’s number, the

flow of vortex ring in a viscoelastic

fluid is different from the one in a

Newtonian fluid, where viscous

stress is linearly proportional to

deformation.

Image 3: Vortex ring in a Newtonian fluid

Image 4: Vortex ring in a Non-Newtonian viscoelastic fluid (sequence from left to right)

The vortex in Newtonian fluid

travels downward and after

sometime, it diffuses. On the

other hand, the vortex ring in

the viscoelastic fluid which

reacts non-linearly to

deformation starts off looking

like a mushroom. Fascinatingly,

it expands as it drops and

contracts as it is “pulled up”.

Both vortex rings were

generated by the same

piston-cylinder apparatus,

same stroke ratio ending

to the same relative

position to the cylinder

exit, also both have the

Reynold’s number = 500.

Velocity for Propagation of a Vortex Ring: Phillip Saffman’s Findings

In an inviscid fluid:

In a viscous fluid,

Image 5: (a) Sketch of a vortex ring with core radius

a, ring radius R, and bubble radius Rb. γ denotes ratio

of semi-minor to semi-major axes. (b) Photograph of

the ring passing through a tracer. Vortex ring can be

seen clearly as the darkest vertical visual in the

middle. Direction of flow: horizontal to the left.

Γ = vortex ring

circulation

R = ring radius

a = core radius of

ring

v = kinematic

viscosity of fluid

T = stroke time

β = constant

assuming a hollow

core

4

Photo credit: J. Albagnac, D. Laupsien and D. Anne-Archard

Photo credit: Ian Sullivan et. al.

𝑅𝑒 =𝜌𝑣𝐿

𝜇

𝑎 = 4𝑣𝑇

The Ongoing Research

Albagnac, J., Laupsien, D. & Anne-Archard, D., 2014. Gallery of

Fluid Motion. [Online]

Available at: http://gfm.aps.org/meetings/dfd-

2014/54081b0c69702d0771020200

[Accessed 21 April 2015].

Gharib, M., Rambod, E. & Shariff, K., 1998. A universal time scale

for vortex ring formation. J. Fluid Mech., Volume 360, pp. 121-

140.

Kelley, P., 2013. Solving a physics mystery: Those ‘solitons’ are

really vortex rings. [Online]

Available at: http://www.washington.edu/news/2014/02/03/solving-

a-physics-mystery-those-solitons-are-really-vortex-rings/

[Accessed 21 April 2015].

McCowan, B. et al., 2000. Bubble Ring Play of Bottlenose

Dolphins (Tursiops truncatus): Implications for Cognition. Journal

of Comparative Psychology, Volume 114(1), pp. 98-106.

Sullivan, I. et al., 2008. Dynamics of thin vortex rings. J. Fluid

Mech., Volume 609, pp. 319-347.

Tomlinson, S., 2014. Meet the Gandalf of volcanoes: Incredible

moment Mount Etna puffs out perfectly formed 50-METRE smoke

rings. [Online]

Available at: http://www.dailymail.co.uk/news/article-

2566812/Incredible-moment-Mount-Etna-puffs-perfectly-formed-

50-METRE-smoke-rings-blue-sky-coast-Sicily.html

[Accessed 20 April 2015].

Volcano Discovery, N.A.. Volcano Photoglossary: Smoke Rings.

[Online]

Available at:

http://www.volcanodiscovery.com/photoglossary/smoke_ring.html

[Accessed 20 April 2015].

When researches at Massachusetts

Institute of Technology witnessed an

unusual “long-lived wave traveling much more

slowly than expected through a gas of cold

atoms”, they called it ‘heavy solitons’ and goes

on to further claim that it defied theoretical

description.

Physicists, Aurel Bulgac and Michael Forbes,

from University of Washington then performs

one of the largest supercomputing (through

the means of two supercomputers, Titan and

Hyak) and later found that the heavy solitons

are likely vortex rings. This enabled them to

demonstrate a simulation that explains the

MIT’s discovery by the concept of vortex

rings.

More importantly, the simulation used “could

revolutionize how we solve certain physics

problems in the future”. This means that there

is a potential that nuclear tests need not to be

performed in order to study nuclear reactions.

Other than that, it could also be beneficial for

comprehension of neutron stars behaviors, for

example, the rapid increase in its pulsation

frequency which is probably caused by inner

star vortex interactions. The certainty of this

is still under active research, an it is one with

much hope. ■

5

Absolem, a

character from

Alice in

Wonderland

making smoke

rings from

smoking a

waterpipe

(hookah).

Photo credit: Google Images