FYFD

Tag: fluid dynamics

  • Where Waves Carry Plastics

    Where Waves Carry Plastics

    The classic theory of steady wave motion predicts a phenomenon called Stokes drift, in which particles spread horizontally in the direction of wave travel. That means that something like microplastics will drift in the direction that waves are traveling. But in the real world, ocean waves aren’t quite so neat and unchanging. A new study looks at what happens when waves are decaying in strength–in other words, what happens in our world when the wind dies down.

    In those circumstances, the researchers found that particles did not just drift horizontally–they drifted vertically, too. Further, how much a particle drifts vertically depends on its initial depth. Since plastics vary in their buoyancy–and can be found in varying numbers and sizes throughout the upper layer of the ocean–this mechanism could significantly affect how waves mix and transport pollution. (Image credit: N. Jensen; research credit: T. Izawa et al.; via Physics World)

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  • Making Quieter Shock Waves

    Making Quieter Shock Waves

    NASA’s X-59 aircraft is intended to demonstrate supersonic flight without the boom. Although it’s broken into supersonic speeds, we haven’t yet heard its “sonic thump” because, so far, it’s been accompanied by conventional supersonic aircraft, which are louder.

    The idea behind the long, skinny X-59 is to create weaker, widely-spaced shocks along the aircraft body. Weaker shocks are easier for atmospheric effects to damp out before they reach the ground, and spacing them out makes it harder for them to “pile up” at the nose and tail to create the strong double shocks that merge into a sonic boom.

    Schlieren image of a model X-59 tested at supersonic conditions in a wind tunnel.
    Schlieren image of a model X-59 tested at supersonic conditions in a wind tunnel. The model is mounted upside-down. The three dark diagonal lines are shock waves originating from the wind tunnel and can be ignored. The fainter lines coming off parts of the aircraft model are the plane’s shock waves.

    NASA is preparing to test the X-59’s in-flight shocks soon, including with in-air schlieren photography like they’ve done in the past for other aircraft. But we’ve already have a glimpse of what to expect, thanks to wind tunnel testing, shown above. Ignore the three dark diagonal lines in the middle of the image (those are from the wind tunnel, not the model aircraft), and focus instead on the thin bright lines coming off the plane. Those are some impressively subtle shock waves!

    Hear more from the aircraft’s designer and test pilots in this Ars Technica article. (Image credit: NASA; see also: Ars Technica, M. Ahaus et al.)

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  • Pacific Surf

    Pacific Surf

    Life in Venice Beach lends itself to wave-watching, or so it seems for photographer Craig Hubbard. His portraits of waves and surfers are ethereal, every swell capped by a cloud-like swath of spray. Somehow, every photographer seems to capture breaking waves a little differently! (Image credit: C. Hubbard; via Colossal)

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  • A Fluidic Space Telescope

    A Fluidic Space Telescope

    A telescope’s resolution is set by the size of its reflective surface. Our largest space telescope, JWST, has a 6.5-meter reflector, the largest we could manage given manufacturing constraints and the need to launch it in a rocket. To reach even larger sizes, researchers are considering a new type of reflector: one made of liquid.

    A fluidic telescope has some obvious advantages: surface tension makes it atomically smooth, and liquids can be packed into any convenient shape for launch. But there are challenges, also. Like, what happens to the reflector when you point it in an new direction?

    That’s what this study looks at, mathematically. Using a mathematical model of a 50-meter-wide, millimeter-thick fluid, the researchers analyzed how different maneuvers over the telescope’s lifetime would affect the image quality.

    Shifting the reflector creates perturbations in the surface, initially at the mirror’s edges. Over time, those perturbations move toward the center of the mirror and, at the same time, decay. The team found that, while typical space telescope operations distorted parts of the mirror beyond the limits of good optical quality, the inner 80% of the mirror could remain undisturbed for twenty or more years. That would be like having a 40-meter telescope in orbit with more than 6x the resolution of JWST. (Image credit: NASA; research credit: I. Gabay et al.)

    An artist's conception of a fluidic space telescope, made with a liquid reflecting surface tens of meters wide.
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  • Mirabilite Mounds at Great Salt Lake

    Mirabilite Mounds at Great Salt Lake

    In cold weather, a new geological feature has shown up at Utah’s Great Salt Lake in the last decade. These salty mirabilite mounds form terraced crystals that resemble Yellowstone’s Mammoth Hot Springs.

    Diagram showing salty springs feeding upward through layers of mirabilite to form a mound aboveground.
    Diagram showing how a salt-laden spring pushing upward through the mirabilite layer can then form mounds at the surface when the dissolved mirabilite recrystallizes after the water evaporates.

    Mirabilite is hydrated sodium sulfate (as opposed to the sodium chloride of table salt). The structures form when upwelling spring water partially dissolves the layer of mirabilite found beneath the lake bed. That sulfate-laden water rises to the surface, where it freezes into the crystals seen here.

    A timelapse showing mirabilite mounds forming.
    A timelapse showing the formation of mirabilite mounds.

    When temperatures rise above freezing, the water in the mirabilite evaporates, leaving behind white, powdery thenardite. (Video credit: Great Salt Lake Institute; image credit: Utah Geological Survey)

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  • Droplets Can Climb Sugar Fibers

    Droplets Can Climb Sugar Fibers

    In nature, droplets and fibers can meet on a spider’s web, on fur, or on a dew-gathering cactus. Here, researchers explore what happens when the droplet can dissolve the fiber it’s suspended on. As the authors note, a lumberjack who cuts the branch they sit on makes a fatal choice. The droplet sees a different outcome.

    As the droplet hangs on the fiber, it dissolves the fiber’s sugar. Dense, sugar-laden water flows downward along the fiber and a replenishing upward flow goes along the droplet’s exterior. Because the sugar concentration is lower near the top of the drop, the fiber thins most quickly there.

    A droplet at the end of a sugar fiber dissolves the fiber, then "jumps" up to the next intact section.
    A droplet hanging at the end of a sugar fiber dissolves the fiber and then “jumps” upward to the next intact portion.

    The droplet has capillary forces along its top and bottom, where it meets the fiber. At the top, the droplet is free to expand, wetting more fiber, but the bottom of the drop is pinned to the fiber. The excess capillary force there goes into compressing the fiber.

    As soon as the fiber breaks, the capillary force is no longer balanced, and the droplet jumps upward. If the drop and fiber are sized just right, the drop will jump upward enough to stay attached to the fiber instead of falling off. (Image and research credit: S. Dorbolo et al.)

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    Inside the LA Aquaduct

    In the early twentieth century, Los Angeles had capital and political willpower, but not water. So it built an engineering marvel, the LA Aquaduct, to guide water from the Sierra Nevadas down to the growing city. Grady gets into the literal (and figurative) ups and downs of the project in this Practical Engineering video.

    Although the engineering prowess of the aquaduct system is impressive, as Grady points out, the LA Aquaduct’s story is much more complicated than the engineering needed to move water between two points. It’s a story where greed, corruption, politics, cultural impact, environment effects, and climate change all intersect. (Video and image credit: Practical Engineering)

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    “Tadpoles: The Big Little Migration”

    Amphibians like toads are often indicator species for their ecosystem because they are vulnerable to changes on both land and water. In this short film, videographer Maxwel Hohn follows the migration of western toad tadpoles in British Columbia, showing their daily underwater journey from deep waters, where they can hide, to warmer, shallow waters, where they eat. Over the days and weeks of their early life, millions of tadpoles make the journey, their bodies morphing as they do. Eventually, they will hop away as toadlets. (Video and image credit: M. Hohn et al.)

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  • Burning Oil Spills With Fire Whirls

    Burning Oil Spills With Fire Whirls

    Though they are relatively infrequent, large marine oil spills, like 2010’s Deepwater Horizon, are devastating and incredibly difficult to clean up. In many locations, the “best” option for responding to such disasters is burning off the oil before it can absorb enough water to sink. But these floating fires leave behind unburned oil and produce soot. To enhance the burn, researchers are looking at the possibility of triggering large-scale fire whirls.

    Often seen in wildfires, these fire vortices are intense and localized. Researchers made a more than 5-meter tall version in these experiments by arranging three walls that spun up the in-flowing air. The fire whirl sat above a pool of water topped in a layer of oil that served as the whirl’s fuel.

    Within the whirl, the fire’s burn rate was 40% higher than a typical pool fire, and soot production was 40% lower–showing that fire whirls can burn cleaner. But the whirls are more finicky to start and maintain. It’s not yet clear whether such intense whirls are possible in the chaotic conditions on the ocean. (Research and image credit: W. Cui et al.; via Eos)

    View of a large-scale fire whirl experiment built around an oil spill on a pool.
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    Fixing Mosul Dam

    Keeping the water in a reservoir is an obvious challenge for any dam. But for Iraq’s Mosul Dam, it’s especially challenging because the dam was built on a foundation of gypsum, a highly water-soluble mineral. Since it was built, Mosul Dam’s water has been eating away at the underlying bedrock, making sinkholes, forcing gaps, and generally working its way out. That, obviously, creates a huge risk for dam failure and massive downstream flooding.

    To get the dam stabilized–at least to a point where Iraqi engineers could keep up with filling the holes as they form–took a massive international engineering project, carried out in the shadow of armed conflict. (Video and image credit: Practical Engineering)

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