FYFD

Tag: 2022gofm

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    Pumping With Faraday Waves

    Vibrate a liquid pool vertically, and it will form a pattern of standing waves known as Faraday waves. Here, researchers confine those waves to a narrow ring similar in size to the wave. The confinement causes a type of secondary flow — a streaming flow — beneath the water surface. As a result, the wave pattern rotates around the ring. The applications of this rotation are pretty neat. As the team demonstrates, it can drive complex fluid networks and even create a pump! (Image and video credit: J. Guan et al.)

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    A Fractal Raft From a Spinning Top

    File this one under Cool Things I Would Have Never Thought Of. In this video, researchers play around with the flow around a spinning top and end up creating a fractal, granular raft. By immersing a top in dyed fluid, they show the toroidal vortices that form around the spinning toy. Then, instead of dye, they add a stretchy elastomer compound that cures over time. The elastomer stretches into thin ligaments in the swirling flow around the top. Eventually, it breaks apart into spherical drops of all different sizes.

    Once the top is removed, the elastomer drops slowly float to the surface. Surface tension and the Cheerios effect draw the drops together, and because of their many sizes, the rafts that form are fractal. (Image and video credit: B. Keshavarz and M. Geri)

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    DIY Superwalking Droplets

    Over the past few years, we’ve seen lots of research in walking droplets, especially as hydrodynamic quantum analogs. But did you know you can replicate this set-up at home and play with it yourself? This video gives an overview of the equipment you’ll need and a simple procedure to follow to get it up and running. From there, your imagination is the limit! (Image and video credit: R. Valani)

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    “Reconfiguring It Out”

    Leaves flutter and bend in the breeze, changing their shape in response to the flow. Here, researchers investigate this behavior using flexible disks pulled through water. The more flexible the disk and the faster the flow, the more cup-like the disk’s final shape. Adding tracer particles to the water allows them to visualize the flow behind the disk. Every disk leaves a donut-shaped vortex ring spinning in its wake, but the more reconfigured the disk, the narrower the vortex. This, ultimately, reduces drag on the disk. That’s why trees in heavy winds streamline their branches and leaves; that flexibility lowers the drag the tree’s roots have to anchor against. (Image and video credit: M. Baskaran et al.)

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    Cleaning the Skies

    Those of us who live in urban environments have experienced the clear, pollution-free air that comes after a rainstorm. But how exactly does rain clean the air? Air pollution typically has both gaseous and particulate components to it. As a raindrop falls, it experiences collision after collision with those particles. Depending on the particle’s surface characteristics — is it hydrophilic or hydrophobic? — and its momentum during impact, it can get trapped in the raindrop, skip off, or even pass through entirely. The physics, it turns out, are identical to those of a rock falling into or skipping off a lake — even though the raindrop and particle might be 1000 times smaller! (Image and video credit: N. Speirs et al.)

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    Flow Between Fibers

    Two vertical fibers, with a gap left between them, form a playground for flow in this Gallery of Fluid Motion video. If the fiber spacing is small enough, the flow will form a stable liquid sheet that runs the full length of the fibers. With a little more distance, though, the fluid forms intermittent bridges, whose spacing depends on flow rate. And when the fibers are not perfectly vertical, even more complex flows are possible. I love how a seemingly simple situation begets such complexity! (Image and video credit: C. Gabbard and J. Bostwick)