Vortices are a common feature of many flows. Here we see a helical vortex tube spinning in a swirling flow. The vortex itself is visible thanks to air trapped in its low-pressure core. As the vortex spins, two sections of it come together. This results in what’s known as vortex reconnection: the vortex lines break apart and rejoin in a new configuration – as a small independent vortex ring and a shorter section of helical vortex. Events like this are common but usually hard to observe directly. They’ve been previously visualized using vortex knots and have even been sighted in the quantum vortices of superfluid helium. (Image credit: S. Skripkin, source; research credit: S. Alekseenko et al., pdf)
Tag: vortex
The Japanese Pufferfish
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If you’ve ever dived or snorkeled over a sandy lake or ocean bottom, you’ve probably seen some neat patterns there. But it’s hard to compete with the Japanese pufferfish for pure artistry. This small fish creates enormous and elaborate designs in the sand in order to attract a mate. The male fish moves the sand into place by flapping his fins very close to the surface. Above a critical flapping velocity, his fins generate vortices capable of picking up sand, as seen below. With repeated passes, the fish is able to excavate the trough that is key to his creation. It’s a constant fight against the current, though.
Puffers aren’t the only ones who flap their fins to move the sands. Rays and flounders use this technique to bury themselves and hide (Video credit: BBC Earth; image credit: A. Sauret, source; research credit: A. Sauret et al.)
Turbine Wakes in the Sea
What we we build always has an impact on the environment around us. The white dots you see in the image above are an array of offshore wind turbines, standing in waters 20 to 25 meters deep. The brownish lines extending from each turbine show the underwater wakes of the turbines, colored by the sediment they’ve picked up. As with trees in a snowstorm, the currents flowing past the base of the turbine likely form a horseshoe vortex that lifts up the sediment into the wake. Because the tides in this area reverse direction every six hours, these sediment plumes can appear quite dynamic in satellite imagery, frequently changing strength and direction. (Image credit: NASA Earth Observatory)
Washington Ice Disk
Winter weather in northern latitudes sometimes brings with it unusual phenomena like this ice disk spinning in the Middle Fork Snoqualmie River in Washington state. Photographer Kaylyn Messer ventured out to capture photos and videos of the event over the weekend. There are a couple theories as to how such disks form, but swirling river eddies are a key ingredient. One theory posits that chunks of ice forming on the river get caught up by the spinning eddy and slowly freeze together to form the disk. Another theory proposes that the disks occur when an existing chunk of ice breaks away, gets caught in the spinning eddy and slowly has its edges ground down into a circle. Personally, I lean toward the former explanation, though there is likely grinding at the edges either way. See more about this ice circle over at Messer’s blog. (Image credit: K. Messer; GIF by @itscolossal; via Colossal)
“Gargantua”
Peering into a vortex feels like staring into an abyss in the Julia Set Collective’s “Gargantua”. Like their previously featured works, this video uses a macro perspective on fluid phenomenon to create an alternate sense of scale. Instead of a whirlpool, we could be observing a wormhole. Part of this is a matter of fooling our brains with perspective, but it also works because, on some level, we recognize that these same fluid patterns occur at very different lengthscales and so it is believable that what we see is much bigger than in reality. (Video credit and submission: S. Bocci/Julia Set Collective)
Dust Devils
Dust devils, like fire tornadoes and waterspouts, form from warm, rising air. As the sun heats the ground to temperatures hotter than the surrounding atmosphere, hot air will begin to rise. When it rises, that air leaves behind a region of lower pressure that draws in nearby air. Any vorticity in that air gets intensified as it gets pulled toward the low pressure area. It will start to spin faster, exactly like a spinning ice skater who pulls in his arms. The result is a spinning vortex of air driven by buoyant convection. On Earth, dust devils are typically no more than a few meters in size and can only pick up light objects like leaves or hay. On Mars, dust devils can be hundreds of meters tall, and, though they’re too weak to do much damage, they have helpfully cleaned off the solar panels of some of our rovers! (Image credit: T. Bargman, source; via Gizmodo)
Bubble Tricks
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Everyone remembers playing with soap bubbles as a child, but most of us probably never became as adept with them as magician Denis Lock. In this video, Lock shows off some of the clever things one can do with surface tension and thin films. My favorite demo starts at 1:25, when he constructs a spinning vortex inside a bubble. He starts with one big bubble and adds a smaller, smoke-filled one beneath it. Then, using a straw, he blows off-center into the large bubble. This sets up some vorticity inside the bubble. When he breaks the film between the two bubbles, the smoke mixes into the already-swirling air in the larger bubble. Then he pokes a hole in the top of the bubble. Air starts rushing out the deflating bubble. As the air flows toward the center of the bubble, it spins faster because of the conservation of angular momentum and a miniature vortex takes shape. (Video credit: D. Lock/Tonight at the London Palladium/ via J. Hertzberg)
Reader Question: Shower Curtains
Reader thansy asks:
Why do the bottoms of shower curtains drift in toward the water coming from the shower head?
We all know that moment. You’re minding your own business, scrubbing away, and all of a sudden, the shower curtain billows up and grabs you. Scientists have debated the cause of this behavior for years. Some argued that the curtain billowed due to hot air rising from the shower. Others claimed the fast-moving spray caused lift that pulled the curtain up. But fifteen years ago, one scientist tackled the problem computationally. He performed a numerical simulation of a shower head spraying into a bath and found that this spray of droplets creates a weak horizontal vortex in the shower.
This shower vortex has a low-pressure core at the middle, which is thought to provide the suction that causes the shower curtain to billow. The scientist, David Schmidt, was awarded the 2001 Ig Nobel Prize for his work. (Image credits: N. Paix, D. Schmidt; research credit: D. Schmidt)
Fire Tornadoes in Action
Commonly called fire tornadoes, these terrifying vortices often occur in large wildfires and have more in common with dust devils or waterspouts than true tornadoes. They form when warm, buoyant air rises due to the fire’s heat. This creates low pressure over the fire source and draws in fresh, cooler air from the surroundings. If there is any small vorticity or rotational motion to that surrounding air, its spin will be amplified as it gets drawn in. This is akin to an ice skater spinning faster when she pulls her arms in – it’s a result of conservation of angular momentum. That intensification of the air’s rotation is what forms the vortex, which we see here due to the flames it draws upward. This footage was captured yesterday by crews fighting fires in Missouri. (Image credit: Southern Platte Fire Protection District/WCPO 9, source)
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Perching Physics
Compared to birds, manmade aircraft tend to be quite limited and inelegant. Fixed-wing aircraft, for example, require long, flat areas for take-off and landing, whereas birds of all sizes are adept at maneuvers like perching. This video examines the perching behaviors of large birds and extends the physics to a small unmanned aerial vehicle (UAV). As a bird approaches a perching location, it pitches its body and wings upward. This places the bird in what’s known as deep stall, where air flowing over the upper surface of the wing separates just after the leading edge. This move dramatically increases drag on the bird, slowing it for landing. At the same time, the speed of the pitch maneuver generates a vortex on the wing that helps the bird maintain lift despite the drop in speed. With the help of both forces, the bird can make a graceful, controlled landing in only a short distance. (Video credit: J. Mitchell et. al.)
