What happens to a droplet hanging on a wire when the wire gets plucked? That’s the fundamental question behind this video, which shows the effects of wire speed, viscosity, and viscoelasticity on a drop’s detachment. With lovely high-speed video and close-up views, you get to appreciate even subtle differences between each drop. Capillary waves, viscoelastic waves, and Plateau-Rayleigh instabilities abound! (Video and image credit: D. Maity et al.)
Phytoplankton blooms have blossomed in coastal waters around the world, driven by phosphorus and nitrogen in agricultural run-off. These large algal blooms deplete oxygen in the water, creating dead zones where fish and other marine life cannot survive. Typically, oxygen makes its way into the ocean at the surface, where breaking waves trap air in bubbles that, when tiny enough, dissolve their oxygen into the water. But this process mainly helps surface-level waters, and without means to circulate oxygen-rich water down to the depths, the low-oxygen state persists.
Artificial reoxygenation is a possible countermeasure. Either by bubbling oxygen directly into deeper waters or by pumping surface-level water downward, we could increase oxygen levels in the water column. So far, though, artificial reoxygenation’s success has been limited; tests in a few bays and estuaries show that it’s possible to reoxygenate the water, but the effects only last as long as the artificial mechanism remains active. Stop the pumps and bubblers and the water will revert to its low-oxygen state in just a day. Even so, the measures may be worthwhile on a temporary basis in some places while we adjust agricultural practices and try to mitigate warming. (Image credit: Copernicus Sentinel/ESA; via Eos)
This JWST image shows a couple of Herbig-Hero objects, seen in infrared. These bright objects form when jets of fast-moving energetic particles are expelled from the poles of a newborn star. Those particles hit pockets of gas and dust, forming glowing, hot shock waves like those seen here in red. The star that birthed the object is out of view to the lower-right. The bright blue light surrounded by red spirals that sits near the tip of the shock waves is actually a distant spiral galaxy that happens to be aligned with our viewpoint. (Image credit: NASA/ESA/CSA/STScI/JWST; via APOD)
Drops impacting a dry hydrophilic surface flatten into a film. Drops that impact a wet film throw up a crown-shaped splash. But what happens when a drop hits the edge of a wet surface? That’s the situation explored in this video, where blue-dyed drops interact with a red-dyed film. From every angle, the impact is complex — sending up partial crown splashes, generating capillary waves that shift the contact line, and chaotically mixing the drop and film’s liquids. (Video and image credit: A. Sauret et al.)
While much attention is given to the summer loss of sea ice, the birth of new ice in the fall is also critical. Ice loss in the summer leaves oceans warmer and waves larger since wind can blow across longer open stretches. Those warmer waters and more dynamic waves affect how ice forms once autumn sets in. Higher waves mean that ice tends to form in “pancakes” like those seen here. Pancake ice is small — typically under 1 meter wide — and can only be observed from nearby, since they’re smaller than typical satellite resolution. Only once there’s enough pancake ice to dampen the waves will the pieces begin to cement together to form larger pieces that will form the basis of the year’s new ice. (Image credit: M. Smith; see also Eos)
Supersonic commercial travel was briefly possible in the twentieth century when the Concorde flew. But the window-rattling sonic boom of that aircraft made governments restrict supersonic travel over land. Now a new generation of aviation companies are revisiting the concept of supersonic commercial travel with technologies that help dampen the irritating effects of a plane’s shock waves.
One such company, Boom Supersonic, partnered with NASA to capture the above schlieren image of their experimental XB-1 aircraft in flight. The diagonal lines spreading from the nose, wings, and tail of the aircraft mark shock waves. It’s those shock waves’ interactions with people and buildings on the ground that causes problems. But the XB-1 is testing out scalable methods for producing weaker shock waves that dissipate before reaching people down below, thus reducing the biggest source of complaints about supersonic flight over land. (Image credit: Boom Supersonic/NASA; via Quartz)
Sound, vibration, and motion are all inextricably linked. In this BBC video, physicist Helen Czerski shows how an object’s sound and vibrations relate through the classic Chladni experiment. She vibrates a metal plate scattered with sand. At most vibration frequencies, the particles of sand bounce all over the place with no distinctive pattern. But at an object’s natural frequencies, there are standing waves and the sand gathers in spots where the standing wave has no vertical motion. The higher the vibration frequency, the more complex the pattern the sand makes. All of this plays into the sounds we hear, too. When struck, an object vibrates at many of its natural frequencies at once. That’s what gives us a rich, musical tone — all those layered frequencies. (Video and image credit: BBC)
Inside a combustion chamber, temperature fluctuations can cause sound waves that also disrupt the flow, in turn. This is called a thermoacoustic instability. In this video, researchers explore this process by watching how flames move down a tube. The flame fronts begin in an even curve that flattens out and then develops waves like those on a vibrating pool. Those waves grow bigger and bigger until the flame goes completely turbulent. Visually, it’s mesmerizing. Mathematically, it’s a lovely example of parametric resonance, where the flame’s instability is fed by system’s natural harmonics. (Video and image credit: J. Delfin et al.; research credit: J. Delfin et al. 1, 2)
Our oceans absorb large amounts of atmospheric carbon dioxide. Liquid water is quite good at dissolving carbon dioxide gas, which is why we have seltzer, beer, sodas, and other carbonated drinks. The larger the surface area between the atmosphere and the ocean, the more quickly carbon dioxide gets dissolved. So breaking waves — which trap lots of bubbles — are a major factor in this carbon exchange.
This video shows off numerical simulations exploring how breaking waves and bubbly turbulence affect carbon getting into the ocean. The visualizations are gorgeous, and you can follow the problem from the large-scale (breaking waves) all the way down to the smallest scales (bubbles coalescing). (Video and image credit: S. Pirozzoli et al.)
When two liquid jets collide, they form a thin liquid sheet with a thicker rim. That rim breaks into threads and then droplets, forming a well-known fishbone pattern as the Plateau-Rayleigh instability breaks up the flow. This poster shows a twist on that set-up: here, the two colliding jets vary slightly in their velocities. That variability adds a second instability to the system, visible as the wavy pattern on the central liquid sheet. The sheet’s rim still breaks apart in the usual fishbone pattern, but the growing waves in the center of the sheet eventually that structure apart as well. (Image credit: S. Dighe et al.)
