(1) In zero gravity, a drop launched at a source fluid of saline solution. The fluid container has a diameter of 4 inches.
Fluid Mechanics in Zero-Gravity
This work involves a phenomenon of broad scientific and practical interest:
The tuning of splash ejecta. Many people have seen Edgerton's 1954 high-speed
photographs of a drop hitting a liquid surface which creates a "crown of
thorns" produced by the impact. The height of the central "Worthington jet"
can be tuned via the velocity of the impactor and the thickness of the target
fluid.
Physics undergraduates Dorothy Caplow and Lisa Couret have investigated
how Edgerton's experiments would need to be done in the absence of gravity.
The images below show some results of their experiments on NASA's Boeing
KC-135A turbo jet parabolic flight program. Small droplets (4 mm in diameter)
are launched into a liquid film ( 8 mm in depth) and their dynamics are captured
on high-speed video. The flights allowed approximately 30 seconds of zero
gravity and similar intervals of 2 g. The initiation of the aircraft free
fall creates inertial ringing in the fluid superposed upon which is a higher
frequency "g-gitter". Dramatic changes are seen in the height of the Crown
and the Worthington jet relative to those in 1 g.
|
(1) In zero gravity, a drop launched at a source fluid of saline solution. The fluid container has a diameter of 4 inches. |
(2) After impact the recoil creates a crown that appears
to be just beginning to undergo an instability at the rim.
In zero g, it was often the |
(3) In 2 g after impact of the incoming droplet a Worthington
jet is ejected. Near the jet tip we see the break up of the
jet in analogy with |
(4) The complete breakup of the Worthington jet is realized one thirtieth of a second later. |
(5) Edgerton's "crown of thorns" in zero g milk.
The height of the rim is approximately 2.5 cm. Jens Eggers |
(6)
A movie of the splash from an actual kitchen faucet.
(7) A movie
of the splash in a zero g actual kitchen faucet.
Move through this movie slowly to see the detail.
(8) A
major difficulty in the flight experiments was to stabilize the source fluid
. Saline solution does not wet the plexiglass source fluid container and
hence in a static situation, surface tension will maintain the integrity
of the target fluid. However, on initiation of a free fall, the inertial
effects from the rollover often substantially disrupted the source fluid.
Here, a particularly strong effect is observed. In zero g the fluid "fought"
the inertial effects by trying to maintain the nonwetting contact angle.
Surface tension suppresses short wavelength fluctuations, and hence the inertial
effects manifest themselves at a rather long wavelength at which there are
available stabilizing mechanisms. In real time the fluid flows as if it were
highly viscous, until it gathesr enough mass to break free of the container.
See more at the Edgerton Center page
This work was partially supported by NASA's Reduced Gravity Student Flight
Opportunities Program directed by Burke Fort and operated out of the Johnson
Space Center in Houston, and the Microgravity Materials Science Program under
the direction of Dr. Mike Wargo.
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