FYFD

Tag: fluid dynamics

  • Jovian Polar Vortices

    Jovian Polar Vortices

    Jupiter’s atmosphere is full of enduring mysteries, and its poles are no exception. Instruments aboard the Juno spacecraft have gotten a better look at Jupiter’s North and South poles than any previous mission, and what they’ve found raises even more questions. Both of Jupiter’s poles feature a central cyclone ringed by other, similarly-sized cyclones. The North pole has eight outer cyclones (top image), while the South pole has five (bottom image), shown above in infrared. Despite being close enough that their spiral arms intersect, the cyclones don’t seem to be merging into something like Saturn’s polar hexagon. For now, scientists don’t know how this arrangement formed or why it persists, but the longer Juno can study the vortices up close, the more we’ll learn. (Image credit: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM; research credit: A. Adriani et al.; submitted by Kam-Yung Soh)

  • Absorbing Bubbles

    Absorbing Bubbles

    This is a bubble absorber. It’s formed from an array of three springs, seen end-on in the upper center, each of which is coated to make it superhydrophobic. The hollow interior of the springs is filled with air and ventilated to the atmosphere. As bubbles rise through the water, they contact the springs and readily coalesce with the interior gas. In the blink of an eye, the large bubble is almost completely absorbed into the thin air film that clings to the springs. Superhydrophobic arrays like these may be useful in power and life support systems that need to separate liquid and gas phases under low-gravity conditions. (Image credit: N. Pour and D. Thiessen, source)

  • Nautilus Swimming

    Nautilus Swimming

    The shellbound chambered nautilus is a champion of underwater jet propulsion. It can eke out efficiencies as high as 75%, far outclassing other jet-based swimmers like squid, salps, and jellyfish. That high efficiency is especially important for the nautilus, which spends a great deal of time at depths where the oxygen needed to fuel movement is in short supply. To get around, the nautilus draws water in through an enlarged orifice, then squirts it out little by little. Its this asymmetry between drawing in and expending that keeps efficiency high. By releasing a jet slower and at lower speeds, the nautilus is able to reduce wasteful losses to friction and thereby keep the efficiency high. The drawback is that the nautilus swims relatively slowly at an average of around 8 centimeters–less than one body length–per second. (Image credit: Simon and Simon Photography/University of Leeds; research credit: T. Neil and G. Askew; via NYTimes; submitted by Kam-Yung Soh)

  • Caught in a Whirl

    Vortex rings may look relatively calm, but they are concentrated regions of intensely spinning flow, as this poor jellyfish demonstrates. The rings form when a high-speed fluid gets pushed suddenly (and briefly) into a slower fluid. In the case of this bubble ring, a burst of air is pushed by a diver into relatively still water. The vorticity caused by the two areas of fluid trying to move past one another forms the ring. Like a spinning ice skater who pulls his arms inward, the narrow core of the vortex spins fast due to the conservation of angular momentum. Meanwhile, the bubble ring moves upward due to its buoyancy, pulling nearby water in as it goes. This catches the hapless jellyfish (who relies on vortex rings itself) and gives it quite a spin. But. don’t worry, the photographer confirmed that the jelly was okay after its ride. (Video credit: V. de Valles; via Ashlyn N.)

  • Castle-like Clouds

    Castle-like Clouds

    An astronaut captured this towering cloud over Andros Island from orbit aboard the ISS. This is a cumulus castellanus cloud, named for the castle-like crenelations at its top. Castellanus clouds form in areas with strong vertical updrafts, often due to cloud-level atmospheric instabilities rather than heating at the Earth’s surface. These clouds frequently proceed rain or even thunderstorms. What distinguishes castellanus from other types of cumulonimbus clouds is their shape: castellanus clouds have protrusions that are taller than they are wide – like the castles for which they are named. (Image credit: NASA / Expedition 48; via NASA Earth Observatory)

  • Modons

    Modons

    The spin of the Earth creates myriad eddies in our oceans, most of which move slowly westward at a speed dependent on their latitude. You can see many in the animation above as green and red rings slowly marching to the left. According to theory, it’s possible for two of these eddies to combine to become more than the sum of their parts; under the right conditions, the two conjoined eddies could become a modon, which, like a vortex ring, is capable of traveling far faster than its parental eddies. Despite the theory, however, no one had ever observed a modon in nature.

    A new paper uses satellite imagery to identify nine modons in different locations around the world. One is shown above. Watch the eastern coast of Australia carefully, and you’ll see a modon form. It moves much faster than its surroundings, first southward toward Tasmania, then quickly eastward toward New Zealand. Thin black circles mark the two eddies that make up the modon. The strength and speed of these features makes them capable of pulling significant water mass with them. This suggests that they may play a role in ocean life, transporting water of different temperatures and nutrient content into regions it would not otherwise reach. (Image and research credit: C. Hughes and P. Miller; via Gizmodo)

  • Chemistry in Infrared

    Chemistry in Infrared

    Many chemical reactions, and the flows that accompany them, are invisible to the human eye. But in infrared wavelengths those same events are vibrant and energetic. In this video from the Beauty of Science group, various chemical reactions are shown in visible and IR wavelengths, revealing very different perspectives on the same thing. Many of the reactions are exothermic, meaning that they produce heat as they occur. Because of this the thermal imaging shows where the most intense reaction is occurring at a given time. Other areas gradually darken as diffusion and flow move and dilute the heat energy released. (Video and image credit: Beauty of Science, source)

  • Hairy Tongues Help Bats Drink

    Hairy Tongues Help Bats Drink

    Nectar-drinking bats, honey possums, and honeybees all use hair-like protrusions on their tongues to help them drink. In bats, these papillae have blood vessels that swell when drinking, stiffening the hairs. To investigate this drinking mechanism, researchers built their own version of a bat tongue by fabricating hairy surfaces and testing how well they trapped viscous oil when dipped and withdrawn. Through a combination of experiment and mathematical modeling, the researchers found that the optimal fluid uptake depended on the density of hairs, fluid viscosity, and the withdrawal speed. When they compared their results to actual bats, honey possums, and honeybees, they found that those animals’ tongues have hair densities very close to the predicted optimal value, suggesting that their model is capturing the important physical mechanisms that have driven evolutionary advantages for these species. (Image and research credit: A. Nasto et al.; submitted by Kam-Yung Soh)

  • When Friction Isn’t Enough

    When Friction Isn’t Enough

    If you try to build a pyramid of dry glass beads, you’ll have a hard time of it. The frictional forces simply aren’t enough to hold the beads together against the force of gravity. If you add a little water, though, the story is different. The intermolecular forces inside water give it a lot of cohesion, which helps it fill the narrow gaps between beads. That added capillary force gives just enough additional sticking power to hold a pyramid of beads together. (Image and video credit: amàco et al.)

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    Skiing, Avalanches, and Freezing Bubbles

    To wrap up our look at Olympic physics, we bring you a wintry mix of interviews with researchers, courtesy of JFM and FYFD. Learn about the research that helped French biathlete Martin Fourcade leave PyeongChang with 3 gold medals, the physics of avalanches, and how bubbles freeze. 

    If you missed any of our previous Olympic coverage, you can find our previous entries on the themed series page, and for more great interviews with fluids researchers, check out our previous collab video. (Video credit: T. Crawford and N. Sharp; image credits: GettyImages, T. Crawford and N. Sharp)