FYFD

Category: Phenomena

  • Featured Video Play Icon

    Convection in Action

    We’re surrounded daily by convection — a buoyancy-driven flow — but most of the time it’s invisible to us. In this video, Steve Mould shows off what convection really looks like with some of his excellent tabletop demos. The first half of the video gives profile views of turbulent convection, with chaotic and unsteady patterns. When he switches to oil instead of water, the higher viscosity (and lower Reynolds number) offer a more structured, laminar look. And finally, he shows a little non-temperature-dependent convection with a mixture of Tia Maria and cream, which convects due to evaporation changing the density. (Image and video credit: S. Mould; submitted by Eric W.)

  • Saharan Dust

    Saharan Dust

    In late January, dust from the Sahara blew westward toward the Cabo Verde archipelago before turning northward toward Europe. During winter and spring, Saharan dust tends to stay at lower altitudes, where it can be carried by the northeast trade winds. In contrast, from late spring to early fall, dust rises higher, carried westward by the Saharan Air Layer; there, the dust can help suppress both the formation and intensity of the Atlantic’s hurricanes.

    On the left side of the image scant clouds trace von Karman vortex streets behind the archipelago, marking the atmospheric disruption caused by the rocky islands. (Image credit: L. Dauphin; via NASA Earth Observatory)

  • Featured Video Play Icon

    Moths in Flight

    Moths and butterflies are such unique fliers among insects. Compared to their bodies, their wings are often enormous. High-speed video reveals the complex motions of their wing strokes. Some species have wings that flex dramatically, bringing sections of the opposite wing close enough to clap together. Other species, like the plume moth, have porous wings that resemble feathers. For these fliers, viscosity provides some resistance to keep air from simply flowing through the wing. But the little bit of air that does get through may help the moth aerodynamically. (Image and video credit: A. Smith/Ant Lab)

  • Swirls Off South Australia

    Swirls Off South Australia

    Summer winds along Australia’s Bonney Coast push coastal waters offshore, triggering the upwelling of colder waters from depths below 300 meters. These cold waters from the deep are nutrient-rich, thanks to all the decomposition that happens along the ocean floor. The infusion of nutrients triggers an explosion of life, visible here in the form of a green phytoplankton bloom along the shelf break. In turn, the phytoplankton attract fish and blue whales. Even great white sharks are drawn to the cornucopia. (Image credit: W. Liang; via NASA Earth Observatory)

  • Rough Surfaces

    Rough Surfaces

    In fluid dynamics, we’re often concerned with flow moving past a solid surface — air past an airplane wing, water past fish scales, oil between moving parts — and those surfaces are rarely perfectly smooth. Rough surfaces affect the flow near them, sometimes in unexpected ways. Here, researchers show a rough surface’s effect on the eddies of the atmospheric boundary layer. Put differently, this poster shows how buildings, trees, and other features influence the lowest layer of the atmosphere. From the tiny gaps between buildings to the eddies towering many times higher, the turbulence reflects roughness’s effects. (Image credit: J. Kostelecky and C. Ansorge)

  • Featured Video Play Icon

    Tracking Break-Up

    In fluid dynamics, researchers are often challenged with complicated, messy flows. With so much going on at once, it’s hard to work out a way to keep track of it all. Here, researchers are looking at the break-up of two colliding liquid jets. This setup is often used to break rocket fuel into droplets prior to combustion. This video shows off a new data analysis tool that lets researchers break the flow into different parts, track them in time, and extract data about the changes that happen along the way. (Video and image credit: E. Pruitt et al.)

  • Featured Video Play Icon

    Shredding Gold

    While vacuums can do pretty wild things to liquids, the title of this Slow Mo Guys video is a bit misleading. They’re not so much exploding gold in a vacuum as they are shredding it during repressurization. Regardless, the visuals are pretty awesome. They place thin foils in a vacuum chamber, pump it down, and then film what happens when they reopen the valve and pressurize the chamber. Flow-wise, that introduces a strong air jet that flows downward in the center of the chamber and causes a recirculating flow up the sides. For the foils, this sudden flow is devastating, shredding the material so thoroughly that it looks like a splash. (Video and image credit: The Slow Mo Guys)

  • Seeding Clouds

    Seeding Clouds

    In the remote South Atlantic, north of the Antarctic Circle, sit the volcanic Zavodovski and Visokoi islands. Though only roughly 500 and 1000 meters tall, respectively, each island disrupts the atmosphere nearby, often generating cloudy wakes. In today’s pair of images, the northerly Zavodovski has a particularly bright cloud wake, thanks to sulfate aerosols degassing from its volcano, Mount Curry. Though it’s hard to pick out the effect in the natural-color image above, the false-color version below shows the bright wake clearly. The filtering on this image turns snow and ice — like that on Visokoi’s peak — red and makes the water vapor of clouds white. The sulfates from Mount Curry act as nucleii for water droplets, forming many small, reflective drops that stand out against the rest of the sky. (Image credit: W. Liang; via NASA Earth Observatory)

    This false-color satellite image highlights the volcanic seeding by filtering snow and ice as red and water vapor in clouds as white.
    This false-color satellite image highlights the volcanic seeding by filtering snow and ice as red and water vapor in clouds as white.
  • Featured Video Play Icon

    Spreading Frost

    Condensation forms beads of water on a surface. When suddenly cooled, those drops begin to freeze into frost. This video looks at the process in optical and in infrared, revealing the patterns of spreading frost and the tiny ice bridges that link one freezing drop to the next. (Video and image credit: D. Paulovics et al.)

  • Mocha Diffusion

    Mocha Diffusion

    These firework-like patterns spread when dyes are added atop a viscous but miscible lower fluid layer. Here, researchers use lower layers like corn syrup and xanthan gum; then they spread dye mixtures including ammonia and vinegar atop those layers. Because the upper and lower layers of fluid are miscible and can diffuse into one another, they together form elaborate patterns. The mixing of the two layers creates gradients in surface tension that can drive the flow and create these mocha diffusion patterns. (Image credit: T. Watson and J. Burton)