Upload
lily-mazlan
View
240
Download
0
Embed Size (px)
Citation preview
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