FYFD

Tag: flow visualization

  • Butterfly Scales

    Butterfly Scales

    Catch a butterfly, and you’ll notice a dust-like residue left behind on your fingers. These are tiny scales from the butterfly’s wing. Under a microscope, those scales overlap like shingles all over the wing. Their downstream edges tilt upward, leaving narrow gaps between one scale and the next. Experiments show that, although butterflies can fly without their scales, these tiny features make a big difference in their efficiency.

    At the microscale, a butterfly's scales overlap like roof shingles but are tilted upward, leaving cavities in the downstream direction.
    At the microscale, a butterfly’s scales overlap like roof shingles but are tilted upward, leaving cavities in the downstream direction.

    When air flows over the scales, tiny vortices form in the gaps between. These laminar vortices act like roller bearings, helping the flow overhead move along with less friction and, thus, less drag. Compared to a smooth surface, the scales reduce skin friction on the wing by 26-45%. (Image credit: butterfly – E. Minuskin, scales – N. Slegers et al., experiment – S. Gautam; research credit: N. Slegers et al. and S. Gautam; via Physics Today)

    This lab-scale experiment shows how air moves over butterfly scales. As flow moves from left to right, small persistent vortices form in the gaps between scales. These act like roller bearings that reduce the skin friction from air moving past.
    This lab-scale experiment shows how air moves over butterfly scales. As flow moves from left to right, small persistent vortices form in the gaps between scales. These act like roller bearings that reduce the skin friction from air moving past.
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    Hitting Molten Steel

    Watching droplets burst is often fascinating, but it’s rare that we get to watch droplets of molten metal. In this Slow Mo Guys video, though, they’re shattering globs of molten steel and filming the results in slow motion. It’s the kind of starburst that breaks compression algorithms but remains beautiful regardless. (Video and image credit: The Slow Mo Guys)

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    “Emerald and Stone”

    “Emerald and Stone” is filmmaker Thomas Blanchard’s tribute to the music of Brian Eno. The short film is made, as Blanchard puts it, with “inks and painting,” but I suspect there’s some oil in there, too, to coat the droplets we see. Much of the movement is likely driven by surface tension variations in the background fluid. I love the effect this has on the droplets. If you watch closely, some of them appear to rotate like a miniature planet; others have counter-rotating sections within the drop. The difference, I suspect, is one of scale: I think the smaller drops rotate altogether while larger ones develop more complex internal flows. (Video and image credit: T. Blanchard)

  • Modeling Wildfires With Water

    Modeling Wildfires With Water

    Turbulence over a burning forest can carry embers that spread the wildfire. To understand how wildfire plumes interact with the natural turbulence found above the forest canopy, researchers modeled the situation in a water flume. Dowel rods acted as a forest, with turbulence developing naturally from the water flowing past. For a wildfire, the researchers used a plume of warmer water, which buoyancy lofted into the turbulence over their model forest.

    The experiment used to model wildfire flows. Dowel rods represent the forest and a plume of warm water (right side; distorting the background) represents the wildfire. The dark device in the foreground is a probe used to measure turbulence.
    The experiment used to model wildfire flows. Dowel rods represent the forest and a plume of warm water (right side; distorting the background) represents the wildfire. The dark device in the foreground is a probe used to measure turbulence.

    The flow over the forest canopy naturally forms side-by-side rolls of air rotating around a horizontal axis. As the buoyant plume rises, it can be torn apart by these rollers, as well as carried downstream. Varying the turbulence, they found, did not affect the average trajectory of the plume. But the more intense the turbulence, the greater the vertical fluctuations in the plume. Those large variations, they concluded, could lift more embers into stronger winds that distribute them further and spread a fire faster. (Image credit: wildfire – M. Brooks, experiment – H. Chung and J. Koseff; research credit: H. Chung and J. Koseff; via APS Physics)

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    To Clog or Not to Clog?

    The clear plastic disks use to study clogging appear rather plain — at least until you look at them through polarizers. Then the disks light up with a web of lines that reveal the unseen forces between the particles. In this video, researchers use this trick to explore how spontaneous clogs occur. If particles jam together into an arch, that bridge can be strong enough to hold the weight of all the particles above it, bringing the flow to a halt. Some arches aren’t strong enough to hold for long; they can break in moments. Other more stable arches persist. By watching the flow through polarizers and carefully tracking the ebb and flow of the forces between particles, researchers can predict which clogs will have staying power. (Video credit: B. McMillan et al.)

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    “Vorticity 5”

    Photographer and stormchaser extraordinaire Mike Olbinski is back with the fifth volume in his “Vorticity” series. Shot over the 2022 and 2023 tornado seasons in the U.S. Central Plains, this edition has virtually everything: supercells, microbursts, lightning, tornadoes, and haboobs. There’s towering convection and churning, swirling turbulence. It’s a spectacular look at the power and grandeur of our atmosphere. (Video and image credit: M. Olbinski)

  • Painting in Sediment

    Painting in Sediment

    Pale plumes of sediment flow off these islands in the Gulf of Mannar between India and Sri Lanka. As waves erode the land, currents and tides carry the sediment outward, shaping it into swirls and eddies. I rarely tire of satellite images like these because there are always subtle new details of flow to notice. The photos are much like paintings, with layer after layer to decipher the closer you look. (Image credit: A. Nussbaum; via NASA Earth Observatory)

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    The Destructive Power of a Blank

    Removing the slug does not make a bullet harmless, as the Slow Mo Guys demonstrate in this video. They’re shooting blanks — casings that still contain propellant but no projectile. There’s still more than enough force to obliterate an egg, lunch meat, and water balloons. You really don’t want one of these fired near you.

    It looks as though the burning propellant is generally the first thing to puncture in each of these. Then the gas from the explosion blows the rest of the object away. The most interesting segment, to me, was the final (pink) water balloon, where the blast wave and its aftermath are visible in a schlieren-like effect that passes over the balloon before its destruction. The sun must have been at just the right position relative to their set-up. (Video and image credit: The Slow Mo Guys)

  • Atlantic Blooms

    Atlantic Blooms

    In April 2023, swirls of green and turquoise burst into vivid color in the Atlantic. Much of the color comes from a phytoplankton bloom. Although phytoplankton are individually microscopic, they form eddies a hundred kilometers across that are visible from space. In detailed images like the one above (available here in full resolution) these swirls have amazing turbulent details. Some of the brightest sections almost look like a field of sea ice! (Image credit: L. Dauphin; via NASA Earth Observatory)

    This wider view shows the bloom's location off of the northeastern U.S.
  • Puddle Depth Matters for Stalagmites

    Puddle Depth Matters for Stalagmites

    In a cave, mineral-rich water drips from the ceiling, spreading ions used to build stalagmites. A recent study considers how the depth of a pool affects the droplet’s splash and how material from the droplet spreads. The authors found several scenarios that vary widely depending on pool depth.

    A droplet falling into a shallow pool creates a splash that quickly breaks up into droplets. This flings the red droplet material in many directions.
    A droplet falling into a shallow pool creates a splash that quickly breaks up into droplets. This flings the red droplet material in many directions.

    A drop falling into a shallow pool had a splash that quickly broke up into droplets (above). By dyeing the pool green and the droplet red, they could track where the droplet’s material wound up. The spray of small droplets carried fluid far, but the main point of impact had a strong concentration of the drop’s fluid.

    With a deeper pool, the drop's impact creates a thick crown splash that collapses in on itself. The drop's fluid is quickly mixed into the pool.
    With a deeper pool, the drop’s impact creates a thick crown splash that collapses in on itself. The drop’s fluid is quickly mixed into the pool.

    In contrast, a deeper pool sent up a thick-walled splash crown that collapsed in on itself. This droplet’s material saw lots of mixing with the pool, but only near the point of impact. From their work, the authors concluded that models of stalagmite growth should incorporate pool depth in order to capture how minerals actually concentrate and move. (Image credit: cave – H. Roberson, others – J. Parmentier et al.; research credit: J. Parmentier et al.; via APS Physics; submitted by Kam-Yung Soh)