A sudden breeze can pluck droplets hanging from a stem. Here, researchers recreate that phenomenon in the laboratory. With a close-up view and high-speed images, we can enjoy every detail of the detachment and break-up. As the wire pulls away, it drags a liquid sheet off the droplet. The thicker rims on either side of the sheet eventually collide, creating a jet that stretches, deforms, and, at last, breaks. (Video and image credit: D. Maity et al.)
Over time, rivers naturally curve and meander. As water accelerates around a river bend’s curve, it creates a secondary flow that carves sediment away from the outer bank and deposits it on the inner one. That, in turn, makes the river bend sharper until it eventually cuts part of the river off into an oxbow lake. In this astronaut photo, we see the Alabama River flowing right-to-left. The river’s natural meander is constrained by the dam on the center left, which widens the river upstream. The higher water level upstream creates the feather-like floodplains lining the river. (Image credit: NASA; via NASA Earth Observatory)
On a vibrating fluid, droplets can bounce and interact in complex ways. Here, researchers demonstrate some of the peculiar dynamics of these wave-guided droplets, showing how they can do things like pair up in waltzes. To keep the droplets from coalescing with one another, they perform their experiments in a pressurized chamber; the higher air pressure makes it harder for the air film between droplets to drain during a collision, making the droplets unable to coalesce. Under these conditions, the authors show that the droplet-wave system has quantum-like statistics. (Video and image credit: J. Clampett et al.)
Peeking between the clouds, satellites caught a glimpse of a massive phytoplankton bloom off the coast of Greenland in May 2024. The tiny organisms may be visible only under a microscope, but gatherings like these stretch hundreds of kilometers and are visible from space. Like tracer particles in a flow, the phytoplankton outline the swirls and eddies of the underlying ocean. (Image credit: L. Dauphin; via NASA Earth Observatory)
Fish detect turbulence in the water around them; among other things, this helps them avoid colliding with objects. Here, researchers are looking to understand how fish interact with underwater turbines. Experiments give them a set of trajectories that actual fish follow when dealing with the experimental turbine. But to understand what the fish is detecting, the researchers build a digital facsimile of the turbine and use Large Eddy Simulation (LES) to calculate the turbine’s wake.
By overlaying the fish trajectories onto the simulated flow structures, they can better understand what flows the fish is and is not comfortable with. That knowledge helps engineers design turbines with smaller ecological impact. (Video and image credit: H. Seyedzadeh et al.)
Many industrial processes break a fluid jet into droplets, like spray painting and ink-jet printing. Here, researchers examine an effervescent fluid jet made up of both liquid and gas. Like a fluid-only jet, this fizzy jet forms sheets, bags, ligaments, and droplets. As it breaks down, it creates a range of droplet sizes–both large and small. But when a shock wave passes, the jet and its droplets get atomized into even tinier droplets. (Video and image credit: S. Rao et al.)
Relatively simple visual and hydrodynamic signals are enough to make digital fish school in ways that resemble living ones. Here, researchers look at what happens when well-behaved schools of fish get too big. The researchers first demonstrate that their schools behave reasonably at one hundred members, either in a schooling configuration or a group milling around a central region.
At one thousand fish, the schools are still reasonably coherent and sensible. But at fifty thousand fish, the picture is drastically different. Neither schooling nor milling groups are able to remain together. They fracture and scatter into smaller groupings. (Video and image credit: H. Hang et al.)
When soap bubbles burst, the hole grows as an expanding circle. But not every fluid bursts this same way. Here, researchers let air rise through oobleck–a fluid made from cornstarch suspended in water–to form a bubble. In time, as with all bubbles, the oobleck bubble bursts. But–in keeping with oobleck’s solid-like properties–the film tears open and fractures. As it sinks back into the liquid, it wrinkles before it slowly relaxes back into fluid form. (Video and image credit: X. Zhang et al.)
When air bubbles rise through a liquid, they scavenge dust, viruses, microplastics, and other impurities as they go. Once at the surface, these contaminant-covered bubbles thin and burst, generating many tiny droplets that arc through the air above. You’re likely familiar with the sight and sensation from a glass of champagne or soda.
Here, researchers have stacked two sets of sequential images to illustrate this complicated flowscape. Under the surface, a trio of photos are stacked to show bubbles rising and gathering at the surface. In the air, the researchers have stacked thirty sequential images, which together trace out the parabolic arcs of droplets sprayed by the bursting bubbles. (Image credit: J. Do and B. Wang)
A slight change in perspective can do wonders. In this video, the Slow Mo Guys look at a burning flame from below. They accomplish this by mounting a gas grill upside-down. This small change means that buoyancy can’t simply lift heat and exhaust gases away from the flame source. Instead, the flow pushes out and around the edges of the grill.
The views are, as always, amazing. The billowing flames are mesmerizing–often closer to laminar than turbulent. And the added spectacle of cinnamon combusting in the later segments really does make for the kind of visuals you’d expect in a sci-fi movie. (Video and image credit: The Slow Mo Guys)
