#capillary waves

[fuckyeahfluiddynamics]

Frog Kick

A toad swims across a pond in this award-winning image from photographer Paul Hobson. The shot was actually captured from below the water, with the camera kept dry in a glass housing. (Image credit: P. Hobson/BWPA; via Colossal)

[fuckyeahfluiddynamics]

Wave Energy Through the Meniscus

Even small changes to a meniscus can change how much wave energy passes through it. A new study systemically tests how meniscus size and shape affects the transmission of incoming waves. (Research and image credit: Z. Wang et al.; via Physics World)

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Oil-Slicked Bubble Bursts

When bubbles at the surface of the ocean pop, they can send up a spray of tiny droplets that carry salt, biomass, microplastics, and other contaminants into the atmosphere. Teratons of such materials enter the atmosphere from the ocean each year. To better understand how contaminants can cross from the ocean to the atmosphere, researchers studied what happens when a oil-coated water bubble pops. (Image credit: Р. Морозов; research credit: Z. Yang et al.; via APS) Read the full article

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Droplet Bounce

A droplet falling on a liquid bath may, if slow enough, rebound off the surface. Its impact sends out a string of ripples -- capillary waves -- on the bath's surface and sends the droplet itself into jiggling paroxysms. (Image and research credit: L. Alventosa et al.; via Dan H.)

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Coalescence Symmetry

When droplets coalesce, they perform a wiggly dance, gyrating as the capillary waves on their surface interfere. When the droplets have matching surface tensions, the coalescence dance is symmetric. But for differing droplets, like water and ethanol, coalescence is decidedly asymmetric. (Image credit: top - enfantnocta, coalescence - M. Hack et al.; research credit: M. Hack et al.)

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Jets Beneath Leidenfrost Drops

When a droplet impacts, it's not unusual for converging ripples to form an upward jet, like the one seen here. But under the right circumstances, jets can form downward, too. (Image credit: water jet - A. Min, others - S. Lee et al.; research credit: S. Lee et al.) Read the full article

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Acoustic levitation and optical tweezers both use waves -- of sound and light, respectively -- to trap and control particles. Water waves also have the power to move and capture objects. (Image and research credit: A. Sherif and L. Ristroph)

[fuckyeahfluiddynamics]

If you take a glass of water and tap on the side of it, you’ll generate waves on the water’s surface. The form of the waves depends on surface tension and gravity, and viscosity governs how quickly the waves fade away. In a recent experiment, researchers performed an equivalent tap for a container of ultra-cold atoms, and the results they found were odd indeed.

The researchers used lithium-6 atoms chilled so close to absolute zero that they could form a superfluid. The “glass” they were contained in consisted of intersecting laser beams, and the “tap” came from toggling the intensity of one of the lasers. This created rippling waves through the atoms that the group could observe. 

Measuring at various temperatures, the group found that the waves in the atoms always decayed the way one expects for a classical fluid like water. Even when the atoms transitioned into a superfluid, the wave decay did not change. Since superfluids are considered to have zero viscosity, you’d expect their waves to decay more slowly, but it turns out, that’s not the case! (Image credit: F. Mittermeier; research credit: M. Zwierlein et al., see also; via Physics; submitted by Kam-Yung Soh)