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  • Pluto: Convection in Sputnik Planum

    Pluto: Convection in Sputnik Planum

    The icy plain of Sputnik Planum, located in Pluto’s heart-shaped Tombaugh Reggio, is criss-crossed with troughs that divide the plain into polygons.  The current interpretation of these features is that they are the result of thermal convection. As with Rayleigh-Benard convection cells on Earth, the interior of the polygons is formed by the upwelling of warmer, buoyant material, and the troughs between cells mark locations where cooled material convects back into the mantle. On Pluto, these cells consist of nitrogen ice (and occasional water ice like the dirty black chunk seen in the upper right photo) that slowly rises and sinks from the planet’s surface, constantly refreshing the surface features. This would explain why Sputnik Planum is missing evidence of typical older features like impact craters. (Image credits: NASA/JHU APL/SwRI)

    Join FYFD all this week for a look at fluid dynamics and planetary science on Pluto! Check out the previous posts here.

  • Pluto: Cryovolcanoes

    Pluto: Cryovolcanoes

    Since its flyby last summer, NASA’s New Horizons mission has had planetary scientists questioning all our assumptions about Pluto and its fellow cold, icy worlds on the outskirts of the solar system. The two mountainous features above, the 4-km tall Wright Mons and 5.6-km tall Piccard Mons, are part of the mystery. Both mountains have a large depression in the middle, and their appearance from orbit is consistent with volcanoes seen on Earth and other planets. But instead of rock, these mountains are formed from water ice, and rather than spewing hot magma, it’s believed that these mountains are cryovolcanoes that erupt with a slurry of water, nitrogen, ammonia, or methane. Since no active eruptions were recorded during the flyby, scientists cannot be certain of the hypothesis, but it does explain the observed features. Check out the video below for a terrestrial demonstration of a “cryovolcano”. (Photo credits: NASA/JHU APL/SwRI; video credit: A. Cheri/U. Wash)

    Join FYFD all this week for a look at the fluid dynamics and planetary science of Pluto!

  • Beach Cusps

    Beach Cusps

    This composite photo shows the arc of the sun over Lulworth Cove in England during the December solstice. The low sun angle reveals a distinctive circular diffraction pattern of waves inside the cove. Along the shoreline, the beach has eroded into a regular, arc-like pattern known as beach cusps. Although there are multiple theories about how cusps form, their pattern is self-sustaining. They consist of a horn of coarse materials that projects into the water and an arc of finer sediments called an embayment. When incoming waves hit the horn, they slow down, depositing heavier coarse sediment on the horn while lighter, fine particles are carried further ashore. (Image credit: C. Kotsiopoulos; via APOD; submitted by jshoer)

  • Falling Ink

    Falling Ink

    Photographer Linden Gledhill created these nebula-like composites from photos of ink diffusing in water. The work was inspired by Mark Stock’s “Spherical Rayleigh-Taylor Instabilities” series featured here last week. Like Stock’s computational art, the twisted fingers and vortex rings above form due to the denser ink falling through less dense water. The interface between the two fluids distorts under the effects of gravity and the fluids’ relative motion. Such shapes are ephemeral at best; the falling ink will quickly become turbulent and diffuse throughout the water.  (Photo credit and submission: L. Gledhill)

  • Collecting Water in the Desert

    Collecting Water in the Desert

    Desert-dwelling plants like cactuses have to be efficient collectors of water. Many types of cactus are particularly good at gathering water from fog that condenses on their spines. Droplets that form near a spine’s tip move slowly but inexorably toward the base of the spine so that the cactus can absorb them. The secret to this clever transport lies in the microstructure of the spine’s surface. The

    Gymnocalycium baldianum cactus, for example, has splayed scales along its spines. Capillary interactions with the scales result in differences in curvature on either side of the droplet. Curved fluid surfaces generate what’s known as Laplace pressure, with a tighter radius of curvature causing a larger Laplace pressure. Because the curvature of the droplet varies from the base side to the tip side of the spine, the difference in Laplace pressures across the droplet creates a force that drives the droplet toward the spine’s base. (Image credit: C. Liu et al., source)

  • Hiding in the Sand

    Hiding in the Sand

    Flounders, stingrays, and other flat, bottom-dwelling fish often hide under sand for protection. These fish move by oscillating their fins or the edge of their bodies. They use a similar mechanism to bury themselves–quickly flapping to resuspend a cloud of particles, then hitting the ground so that the sand settles down to cover them. Researchers have been investigating this process by oscillating rigid and flexible plates and observing the resulting flow. When the flapping motion exceeds a critical velocity, the vortex that forms at the plate’s edge is strong enough to pick up sand particles. Understanding and controlling how and when these vortex motions kick up particles is useful beyond the ocean floor, too. Helicopters are often unable to land safely in sandy environments because of the particles their rotors lift up, and this work could help mitigate that problem. (Image credits: TylersAquariums, source; Richmondreefer, source; A. Sauret, source; research credit: A. Sauret et al.)

  • Drinking in Space

    Drinking in Space

    Earlier this year, the Capillary Beverage experiment launched to the International Space Station with new open-topped “Space Cups” for astronauts to test. Now those of us back on Earth are getting a glimpse of the cups in microgravity action. The geometry of the cups is wide on the back-end with a tightening v-shape near the mouth. This shape guides the liquid by using capillary action to wick it toward the spout.

    One of the key goals of the experiment was to observe how the liquid drained–what shape it assumed in the cup and where and how much liquid was left behind. The researchers want to compare the real-life performance of the cups with their numerical models and simulations, which will help design future microgravity liquid transport systems for fuel, waste management, and other applications.

    Although the experiments have a wider purpose, the space cups also do a great job allowing astronauts to drink from more than just pouches. Check out the gallery demo above to see how they hold up against astronaut silliness! (Video and image credits: NASA/IRPI LLC, GIF source)

  • The Fluidic Oscillator

    The Fluidic Oscillator

    A fluidic oscillator is a device with no moving parts that sprays a fluid from side to side. The animations above illustrate how they work. A nozzle funnels a fluid jet through a chamber with two feedback channels. When the jet sweeps close to one side of the chamber, part of the fluid is directed along the feedback channel and back toward the inlet. That flow feeds into a recirculating separation bubble in the middle of the chamber. As that bubble grows, it pushes the jet back toward the other feedback channel, continuing the cycle. Many automobiles use fluidic oscillators in their windshield washer sprays. Check out the award-winning full video from the Gallery of Fluid Motion.  (Image credit: M. Sieber et al., source)

  • Draining Soap Film

    Draining Soap Film

    The brilliant colors of a soap film are directly related to the film’s thickness. Black regions, like the one in the upper right of this image, are the thinnest regions and may be less than 100 nanometers thick. (That’s smaller than the shortest wavelength of visible light!) The colors of the peacock-feather-like blooms along the bottom of the image demonstrate significant variations in film thickness. This is caused by uneven concentrations of surfactants in the film. The variations in concentration causes differences in local surface tension, which in turn moves fluid around within the film. This is known as a Marangoni effect. (Image credit: S. Berg and S. Troian)

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    Oil Film on Water

    This award-winning short film features a thin layer of volatile oil on water. The oil evaporates quickest from shallow pools only microns deep, which appear bluish in the video. Surface instabilities along the edge of the pool create flow that draws oil in, generating the iridescent droplets seen floating among the evaporation pools. The droplets combine and coalesce as they come in contact with one another. Since droplets have a larger volume per surface area than the shallow pools, they evaporate more slowly. The behaviors observed here are important to applications like oil and fuel spills, which can persist longer if the floating fluid layer tends to form droplets. (Video credit: J. Hart; via txchnologist)

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