jet collision

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On Earth, it’s easy for the effects of surface tension and capillary action to get masked by gravity’s effects. This makes microgravity experiments, like those performed with drop towers or onboard the ISS, excellent proving grounds for exploring fluid dynamics unhindered by gravity. The video above looks at how colliding jets of liquid water behave in microgravity. At low flow rates, opposed jets form droplets that bounce off one another. Increasing the flow rate first causes the droplets to coalesce and then makes the jets themselves coalesce. Similar effects are seen in obliquely positioned jets. Perhaps the most interesting clip, though, is at the end. It shows two jets separated by a very small angle. Under Earth gravity, the jets bounce off one another before breaking up. (The jets are likely separated by a thin film of air that gets entrained along the water surface.) In microgravity, though, the jets display much greater waviness and break down much quicker. This seems to indicate a significant gravitational effect to the Plateau-Rayleigh instability that governs the jet’s breakup into droplets. (Video credit: F. Sunol and R. Gonzalez-Cinca)

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Two jets colliding can form a chain-like fluid structure. With increasing flow rate, the rim of the chains becomes wavy and unstable, forming a fishbone structure where droplets extend outward from the fluid sheet via tiny ligaments. Eventually, the droplets break off in a pattern as beautiful as it is consistent. (Photo credits: A. Hasha and J. Bush)

your deadly perfections

my
words flick
in foreign tongues of
disorganized tidbits
of elocution
tamed
from
your
wild
winds …

they steal the
furnishings of
your languid soul
sitting erotically on
a cell-radio piano patio

in a half-awake
jigsaw jet lag
collision
with
tea-time
eloping words … and

my wings flutter carefully
as my solitude stares
sharply at your mood
already in a dark
submersion

i dream of dead souls
and the excellence
of your manners …

but
your flesh remains
a sword-angel
from long ago
knifing
into
me
for another night
of sordidness -

beautiful and enchanting
you turn my thoughts into
words … mysterious
and unspeakable
decaying little
by little into
freakish
witchy
wordy
poetry …

the deadly perfections of
your wind-storms are
magnificent ordeals
for the soul

your deadly perfections
are worthy of my poetry
and they carve into it
with elegance.

When two liquid jets collide, they can form an array of shapes ranging from a chain-like stream or a liquid sheet to a fishbone-type structure of periodic droplets. This series of images show the collision of two viscoelastic jets–in which polymer additives give the fluids elasticity properties unlike those of familiar Newtonian fluids like water. The jet velocities increase with each image, changing the behavior from a fluid chain (a and b); to a fishbone structure (c and d); to a smooth liquid sheet (e); to a fluttering sheet (f and g); to a disintegrating ruffled sheet (h), and finally a violently flapping sheet (i and j). The behavior of such jets is of particular interest in problems of atomization, where it can be desirable to break an incoming stream of liquid up into droplets as quickly as possible. (Photo credit: S. Jung et al.)

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When two jets of liquid collide, they form a sheet of fluid.  As the speeds of the jets change, the sheet can become unstable, forming a set of liquid ligaments and droplets that look like a fish’s bones. This is shown in the video above. For purposes of orienting yourself, flow in the video is moving right to left and the video has been rotated 90-degrees clockwise (i.e. the two out-of-frame jets forming the flow seen are falling due to gravity). (Video credit: Sungjune Jung, University of Cambridge)