Dynamic Thin Film Phenomena in Microgravity
University of Washington
Edgerton's 1954 high-speed photographs of a droplet hitting a
liquid surface brought aesthetic aspects of fundamental fluid physics to
the public. Although his observations of the "crown of thorns" produced by
the droplet impact still commonly appear in the media, there are many
important aspects of splashing phenomena that are unexplained. Repeating
these experiments in a zero gravity environment may advance our
understanding. Depending on the impacting droplet diameter and its
velocity, a rimmed cavity is created in a fluid surface that spreads
radially and breaks down into periodic array of vertically moving jets, the
tips of which undergo a capillary instability and produce secondary
droplets. I the correct regime, a central vertically moving "Worthington
jet" appears in the middle of the crown and bypasses the surrounding jets.
On Earth, the characteristic shape and evolution of a liquid splash can
result from a competition between capillary, inertial, and gravitational
forces. Under microgravity conditions the latter are negligible so under
some conditions we expect to see novel behavior. Both on earth, and in
microgravity conditions on the FC-135 jet, we will launch liquid droplets
into a shallow liquid film and take high-speed video images of the
resulting splashes. We expect to see changes in the height of the
Worthington jet, and in the length scales associated with the unstable
behaviour of the jets.
Modern applications of splash theory include: meteor impact on
planetary surfaces, underwater acoustics of raindrops, entrainment of air
into liquid surfaces, mineral and organic material deposition during floods
and storms, and hazardous materials processing and fuel containment and
safety.
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