Fabrics flutter in seemingly impossible ways in artist Thomas Jackson‘s images. But despite first appearances, each photograph is true to life; the fabrics are suspended on taut lines. Their dance is driven by wind energy, drag, tension, and flow–not manipulated pixels. I love the (turbulent) energy of them! (Image credit: T. Jackson; via Colossal)
In planetary atmospheres, energy and vorticity can cascade from large scales to smaller ones, but the mechanics of this transfer remain somewhat elusive. In a recent experiment, researchers built a lab-scale representation of an atmosphere using a meter-scale rotating annular tank. The outer bottom edge of the tank gets heated–representing the sun’s warming at the equator–while a pipe in the center of the tank gets cooled near the tank surface, which mimics the chilling effect of the poles. Researchers filled the tank with a water-glycerol mixture and recorded how their artificial atmosphere responded at different rotation rates.
The results show an energy spectrum that’s consistent with atmospheric observations–with a steep drop at large length scales and a flatter one at smaller scales. But interestingly, they also found that the cascade was temperature-dependent in ways that current models don’t predict. Untangling that effect could help us understand not only our atmosphere but those of other planets. (Image credit: tank – H. Scolan, animation – S. Ding et al.; research credit: S. Ding et al.; via APS)
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.)
Flow visualization is both an art and science in fluid dynamics. Here, researchers were interested in studying the separation bubble that forms over a backward-facing ramp–a shape that shows up, for example, on an aircraft. In these areas, the flow over the surface separates, leaving an unsteady, recirculating bubble.
That’s the flow that researchers are visualizing here. They’ve done so by adding tiny helium-filled soap bubbles to the flow. With bright lights illuminating the bubbles, each one leaves a streak in a photograph, showing where the bubble moved during the time the camera’s shutter was open. Although images like these are beautiful, they can also be analyzed by computers to extract the underlying flow that created the image. (Image and research credit: B. Steinfurth et al.; see also here)
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)
Photographer Jan Erik Waider is a master of capturing incredible landscape imagery. In these videos, he uses a drone to film waves in the Baltic Sea gently undulating polygonal slabs of ice on the ocean surface. The interplay of light, color, and motion looks almost surreal, but nature is better than we credit at making imagery too good to look away from. (Video and image credit: J. Waider/NorthLandscapes; via Colossal)
When flow moves past a cylinder, vortices get shed in its wake. Known as a von Karman vortex street, this distinctive pattern is seen behind flags, islands, and even behind starships. Here, researchers are simulating flow of a viscoelastic fluid, where–unlike water or other Newtonian fluids–elastic stresses can build up.
As the flow hits the leading edge of the cylinder, the polymers in the fluid compress and then get stretched as the flow moves around the cylinder. The left image shows vorticity in the flow; the right shows elastic stresses. The large swirls are primary vortices–those shed off the cylinder. But look closely and you’ll see smaller secondary vortices curled up beside the primaries. These form when the elastic stresses in the fluid pull some of the shear layer into the wake. (Image and research credit: U. Patel et al.)
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.)
Although water can freeze below 0 degrees Celsius, it requires a little help–in the form of a nucleation site–to do so. Often temperatures must dip well below 0 degrees Celsius for droplets to become ice. But a new study shows that at least one fungus forms proteins that help the process along.
The proteins come from the Mortierellaceae fungal family, by way of a bacterial species some hundreds of thousands of years ago or more. In experiments, adding the fungal protein helped water freeze 10 or more degrees Celsius sooner than it otherwise would.
The authors note that there are many possible applications for this freezing additive; it could help preserve food or cells without requiring lower freezing temperatures that could damage delicate tissues. It could also serve as a cloud seeding chemical in place of toxic silver iodide particles. (Image and research credit: R. Eufemio et al.; via Gizmodo; see also V. Tech)
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.)