Tag: flow visualization

Strata of Starlings
Starlings come together in groups of up to thousands of birds for the protection of numbers. These flocks form spellbinding, undulating masses known as murmurations, where the movement of individual starlings sends waves spreading from neighbor to neighbor through the group. One bird’s effort to dodge a hawk triggers a giant, spreading ripple in the flock.
To capture the flowing nature of the murmuration, photographer and scientist Kathryn Cooper layers multiple images of the starlings atop one another. The birds themselves become pathlines marking the murmuration’s motion. The final images are surprisingly varied in form. Some flocks resemble a downpour of rain; others the dangling branches of a tree. (Image credit: K. Cooper; via Colossal)
Fediverse Reactions
January 10, 2025
The Best of FYFD 2024
Welcome to another year and another look back at FYFD’s most popular posts. (You can find previous editions, too, for 2023, 2022, 2021, 2020, 2019, 2018, 2017, 2016, 2015, and 2014. Whew, that’s a lot!) Here are some of 2024’s most popular topics:
This year’s topics are a good mix: fundamental research, civil engineering applications, geophysics, astrophysics, art, and one good old-fashioned brain teaser. Interested in what 2025 will hold? There are lots of ways to follow along so that you don’t miss a post.
And if you enjoy FYFD, please remember that it’s a reader-supported website. I don’t run ads, and it’s been years since my last sponsored post. You can help support the site by becoming a patron, buying some merch, or simply by sharing on social media. And if you find yourself struggling to remember to check the website, remember you can get FYFD in your inbox every two weeks with our newsletter. Happy New Year!
(Image credits: dam – Practical Engineering, ants – C. Chen et al., supernova – NOIRLab, sprinkler – K. Wang et al., wave tank – L-P. Euvé et al., “Dew Point” – L. Clark, paint – M. Huisman et al., iceberg – D. Fox, flame trough – S. Mould, sign – B. Willen, comet – S. Li, light pillars – N. Liao, chair – MIT News, Faraday instability – G. Louis et al., prominence – A. Vanoni)
Fediverse Reactions
January 1, 2025
Active Cheerios Self-Propel
The interface where air and water meet is a special world of surface-tension-mediated interactions. Cereal lovers are well-aware of the Cheerios effect, where lightweight O’s tend to attract one another, courtesy of their matching menisci. And those who have played with soap boats know that a gradient in surface tension causes flow. Today’s pre-print study combines these two effects to create self-propelling particle assemblies.
The team 3D-printed particles that are a couple centimeters across and resemble a cone stuck atop a hockey puck. The lower disk area is hollow, trapping air to make the particle buoyant. The cone serves as a fuel tank, which the researchers filled with ethanol (and, in some cases, some fluorescent dye to visualize the flow). Like soap, ethanol’s lower surface tension disrupts the water’s interface and triggers a flow that pulls the particle toward areas with higher surface tension. But, unlike soap, ethanol evaporates, effectively restoring the interface’s higher surface tension over time.
With multiple self-propelling particles on the interface, the researchers observed a rich series of interactions. Without their fuel, the Cheerios effect attracted particles to each other. But with ethanol slowly leaking out their sides, the particles repelled each other. As the ethanol ran out and evaporated, the particles would again attract. By tweaking the number and position of fuel outlets on a particle, the researchers found they could tune the particles’ attractions and motility. In addition to helping robots move and organize, their findings also make for a fun educational project. There’s a lot of room for students to play with different 3D-printed designs and fuel concentrations to make their own self-propelled particles. (Research and image credit: J. Wilt et al.; via Ars Technica)
Fediverse Reactions
December 24, 2024
Inside the Squirting Cucumber
Though only 5 cm long, the squirting cucumber can spray its seeds up to 10 meters away. The little fruit does so through a clever combination of preparation and ballistic maneuvers. Ahead of launch, the plant actually moves water from the fruit into the stem; this reorients the cucumber so that its long axis sits close to 45 degrees. It also makes the stem thicker and stiffer.
This high-speed video shows the explosive release of the squirting cucumber’s seeds.
When the burst happens, fruit spews out a jet of mucus that propels the seeds at up to 20 m/s. The initial seeds move the fastest — thanks to the fruit’s high-pressure reservoir — and fly the furthest. As the pressure drops, the jet slows and the fruit’s rotation sends the seeds higher, causing them to land closer to the original plant. With multiple fruits in different orientations, a single plant can spread its seeds in a fairly even ring around itself. (Research and image credit: F. Box et al.; via Gizmodo)
Fediverse Reactions
December 19, 2024
A Mini Jupiter
Astronaut Don Pettit posted this image of a Jupiter-like water globe he created on the International Space Station. In microgravity, surface tension reigns as the water’s supreme force, pulling the mixture of water and food coloring into a perfect sphere. It will be interesting to see a video version of this experiment, so that we can tell what tools Pettit used to swirl the droplet into the eddies we see. Is the full droplet rotating (as a planet would), or are we just seeing the remains of a wire passed through the drop? We’ll have to stay tuned to Pettit’s experiments to find out. (Image credit: NASA/D. Pettit; via space.com; submitted by J. Shoer)
Fediverse Reactions
December 11, 2024
Predicting Droplet Sizes
Squeeze a bottle of cleaning spray, and the nozzle transforms a liquid jet into a spray of droplets. These droplets come in many sizes, and predicting them is difficult because the droplets’ size distribution depends on the details of how their parent liquid broke up. Shown above is a simplified experimental version of this, beginning with a jet of air striking a spherical water droplet on the far left. In less than 3 milliseconds, the droplet has flattened into a pancake shape. In another 4 milliseconds, the pancake has ballooned into a shape called a bag, made up of a thin, curved water sheet surrounded by a thicker rim. A mere 10 milliseconds after the jet and drop first meet, the liquid is now a spray of smaller droplets.
Researchers have found that the sizes of these final droplets depend on the balance between the airflow and the drop’s surface tension; these two factors determine how the drop breaks up, whether that’s rim first, bag first, or due to a collision between the bag and rim. (Image credit: I. Jackiw et al.; via APS Physics)
December 4, 2024
Growing Downstream
This astronaut photo shows Madagascar’s largest estuary, as of 2024. On the right side, the Betsiboka River flows northwest (right to left, in the image). Less than 100 years ago, most of the estuary was navigable by ships, but now more than half of it is taken up by the river delta. Upstream on the river, extensive logging and expansions to farmland have caused severe soil erosion; the river carries that sediment downstream, dyeing the waters reddish-orange. As the river branches and the flow slows, that sediment falls out of suspension, building up islands and seeding new sand bars further downstream.
A difference of 40 years. A 2024 astronaut photo of the Betsiboka River delta compared with one from 1984 (inset). Several islands are labeled in both images. Notice how new islands have formed upstream of the ones seen in 1984.
In the image above, you can compare the 2024 delta to the way it looked in 1984. Letters A, B, C, and D mark the downstream-most islands from 1984. Today newer islands and sand bars sit even further downstream. (Image credit: NASA; via NASA Earth Observatory)
December 2, 2024
Lines of Ice Eddies
In February 2024, the North Atlantic’s sea ice reached its furthest extent of the season, limning the coastline with tens of kilometers of ice. These images — both capturing the Labrador coast on the same day — show the swirling patterns marking the wispy edges of ice field. In this region, the ice is likely following an eddy in the ocean below. Eddies like these can form along the edges where warm and cold currents meet. An ice eddy is particularly special, though, as the water must be warm enough to fragment the sea ice, but not so warm that it melts the smaller ice pieces. (Image credit: top – NASA, lower – M. Garrison; via NASA Earth Observatory)
This satellite image shows sea ice off the Labrador coast, on the same day in February 2024.
November 27, 2024
Convection in Blue
Convection cells like these are all around us — in the clouds, on the Sun, and in our pans — but we rarely get to watch them in action. Convection results from densities differing in different areas of a fluid. Under gravity’s influence, having a dense fluid over a lighter one is unstable; the dense fluid will always sink and the lighter one will rise. When that motion has to take place across a large surface area, we often end up with cells like the ones seen here.
Convection cells in an alcohol-paint mixture.
What drives the density differences in the fluid? That depends. Often there’s a temperature difference that drives warmer fluid to rise and cool fluid to sink. But that’s not always the source of convection. Evaporating a volatile chemical — like alcohol — out of a mixture can also create the density differences needed for convection. That may be the source of the convection we see here in a mixture of paint and alcohol. (Video and image credit: W. Zhu; via Nikon Small World in Motion)
November 18, 2024
“Last Breath of Autumn”
On a rainy autumn day, Agorastos Papatsanis headed to the forest in search of fungi. There he captured this fairytale-like scene with falling rain and drifting spores. Near the forest floor, any breeze is slight, so mushrooms use their own humidity to move air and spread their spores. As water evaporates from the mushroom’s cap, it cools the air nearby, causing it to spread outward. Since that water vapor is lighter than air, it rises, too, carrying the mushroom’s spores along with it. (Image credit: A. Papatsanis; via Wildlife PotY)
October 25, 2024