Droplets of paint whirl to Chopin’s “Nocturne Op. 9 No. 2” in this short film from artist Thomas Blanchard. The glitter particles in the paints act as seed particles that highlight the flow within and around each drop. It’s a beautiful dance of surface tension, advection, and buoyancy. (Image and video credits: T. Blanchard; via Colossal)
This glimpse inside a 5-day-old zebrafish’s heart shows why they’re often used as a model organism in cardiac studies. The fish’s heart rate is similar to humans and its two-chamber heart — one atrium and one ventricle, both seen here — serves as a simplified version of ours. Check out the slowed-down section of the video to clearly see blood filling and expanding one chamber before it’s pumped onward. Perhaps the most unusual feature of the zebrafish’s heart is its ability to regenerate; after amputation of up to 20% of its ventricle, the fish can fully regenerate its heart. That’s a pretty incredible recovery, especially when you consider that the heart has to keep pumping the entire time! (Video credit: M. Weber/2023 Nikon Small World in Motion Competition)
In the winter, warm air rises from our floor vents or radiators, creating a complex, invisible flow in the background of our lives. Buoyancy lifts warmer air upward while cooler, denser air sinks back down. This thermal convection is everywhere: in our buildings, the ocean, the sky overhead — even in the visible layer of our sun.
In nature, these systems are so large and complex that fully measuring or simulating them remains impossible. Instead, researchers focus on a simplified system — a Rayleigh-Bénard cell — that’s essentially an idealized version of a pot on a stovetop. The lower surface of the cell is heated — like the bottom of a pan on the burner — while the upper surface of the fluid cools. Even this idealized system is a challenge, though, and neither lab-scale versions nor simulations can reach the same conditions that we find in nature.
To bridge the gap, scientists rely on mathematical models — theories built on our best understanding of the physics — and physical analogies to similar systems — like flow over a flat plate — that are “easier” to measure. For a thorough overview of recent work in the area, check out this review in Physics Today. (Image credit: A. Blass; research credit: D. Lohse and O. Shishkina in Physics Today)
In the mid-eighteenth century, pewterer Andreas Wirtz invented a spiral pump. Even today, his design is useful for small-scale, low-power pumping, as seen in this Steve Mould video. The design relies on a series of air and water plugs to build up pressure that’s then used to lift the fluids higher. In the video, Mould visits a stream-powered, home version of a Wirtz pump that regularly delivers water over eight meters in elevation. See it in action in the full video! (Video and image credit: S. Mould)
The Sea of Okhotsk is the northern hemisphere’s southernmost sea that seasonally freezes. Caught between the Siberian coast and the Kamchatka Peninsula, cold air from Siberia helps freeze water kept at lower salinity due to freshwater run-off. This image, taken in May 2023, shows free-floating sea ice forming spirals driven by wind and waves. Small islands off the eastern coast (right side in image) are likely responsible for the swirling eddies seen there. Like phytoplankton blooms and sediment swirls in warmer seasons, the sea ice acts as a tracer to reveal flow. (Image credit: W. Liang; via NASA Earth Observatory)
Artist Dan Coe uses lidar data to create portraits of rivers and their past meanders. Used aerially, lidar produces high-resolution elevation data that provides a glimpse of features that are currently hidden beneath vegetation. With rivers, this means unearthing some of their previous paths. Secondary flows in a river bend erode the bed so that the bend gets more and more strongly curved. Eventually, the river can double back on itself and cut off the long curve. Repeat that process over millennia and you wind up with the complex paths in Coe’s images. (Image credit: D. Coe; via Colossal)
While not directly fluid dynamical, this video from Steve Mould uses water to illustrate mathematical concepts like fractals and space-filling curves. Water, it turns out, does a great job of drawing our eyes to the way these one-dimensional curves fill up two- and three-dimensional space. Check out the full video for a mathematical dive into the concepts. (Video and image credit: S. Mould)
This award-winning video shows blood flowing through the tail fin of a small fish. Cells flow outward in a central vessel, then split to either side for the return journey. In this microscopic video, the speed of individual cells seems quite fast, even though the vessels themselves are only wide enough for the blood cells to move in single file. Flow at the microscale can be counterintuitive like that. (Video and image credit: F. Weston for the 2023 Nikon Small World in Motion Competition; via Colossal)
James Bond notoriously orders his martinis “shaken, not stirred,” a request bartenders fulfill by shaking the cocktail over ice in a separate shaker. But what if you shake the martini glass itself? That’s the question that inspired this lovely mixology.
By shaking the martini glass gently back and forth (along the directions shown by the arrows in each image), the team created different mixing patterns within the glass. With a little food dye and pearl dust, they visualized the flows they found. By changing the viscosity of the cocktail and the speed of the swish, they made everything from a four-leaf clover to a cadre of ghosts. It seems that martini glasses hold a flow for every occasion! (Image and research credit: X. Song et al.; submitted by Zhao P.)
One theory suggests that the Great Sphinx of Giza formed — in part — naturally as a result of erosion, and ancient Egyptians added features to the bedrock formation. To test the plausibility of the theory, researchers made a miniature sphinx, consisting of a clay mound with a single, harder inclusion to represent the Sphinx’s head, and placed their construction in a water tunnel. As the water eroded away the clay, the head appeared, and flow around this harder-to-erode region formed some of the body and paws of the reclining Sphinx.
The experiment suggests that it is plausible for part of the Sphinx to have formed naturally, as a result of erosion. But plausibility is not proof, and given the lack of a contemporary inscription explaining the statue’s origin, the goals and methods of the people who built it around 2500 B.C.E. will remain a matter of archaeological debate. (Image credit: S. Boury et al.)