Vortex rings blown from Mount Etna’s vents drift through the dawn light in this beautiful image from Dario Giannobile. Little is required to create vortex rings — they are a puff of fluid shaped by an orifice — but they are relatively unusual to see around volcanoes. Etna is an exception; it happens to have one or more vents that frequently form rings. Their shape and the venting pattern of the volcano must be unusually well-suited to ring formation. (Image credit: D. Giannobile; via APOD)
Tag: vortex rings
Etna’s Blowing Rings
Mount Etna has long been known for its smoke rings, but thanks to the opening of a new vent on the volcano’s southeast crater, it’s now making more rings than ever. Etna’s smoke rings are, more precisely, vortex rings — produced in the same way dolphins, swimmers, and whales make vortex rings: a sudden push of air through a roughly circular opening. It’s likely that Etna and other volcanoes make far more rings than those we see; we’re limited to noticing only the ones that entrain smoke and condensation to make them visible. (Video and image credit: The Straits Times; via Colossal)
Supernova Rings
Some 20,000 years ago, a massive star blew off a ring of dust and gas that expanded into the surrounding interstellar medium. Later, in 1987, the star exploded as supernova 1987A. That explosion lit the surrounding area, revealing a clumpy ring astronomers have struggled to explain. But a new team believes they have a fluid dynamical answer: the Crow instability.
Closer to home, we see the Crow instability when an airplane’s contrails break up. It happens when two vortices that rotate in opposite directions are close to one another. Any wobble in one vortex is enhanced by the influence of its neighbor. Eventually, this breaks the original vortices apart and causes them to reform as a series of smaller vortex rings.
A comparison between an image of SN 1987A and an illustration of the vortex ring interaction thought to create that shape. In the case of supernova 1987A, the researchers propose that the star originally blew off two vortex rings that, due to their mutual influence, broke down into a clumpy ring of vortices. (Image credits: NASA/ESA/CSA/M. Matsuura/R. Arendt/C. Fransson and NASA/ESA/A. Angelich + M. Wadas et al.; research credit: M. Wadas et al.; via APS Physics)
Vortex Below
When a drop of ethanol lands on a pool of water, surface tension forces draw it into a fast-spreading film. Evenly-spaced plumes form at the edges of the film, then the film stops spreading and instead retracts. All of this takes place in about 0.6 seconds. But, as the image above shows, there’s more that goes on beneath the surface. A vortex ring forms and spreads under the film, driven by the shear layer under the edge of the plumes. Here, the vortex ring is visible in the swirling particles near the water surface. (Image and research credit: A. Pant and B. Puthenveettil)
Vortex Rings From a Square Outlet
When a vortex ring forms, it’s often from fluid forced through a round outlet, whether that’s someone’s mouth, a pipe, or a dolphin’s blowhole. But vortex rings can come from other shapes, too. This video shows us several examples, including slots and square outlets. The vortex rings blown from a square outlet are messier but still recognizable. The slot-shaped outlets produce even neater results, including twin vortex rings that move parallel to one another! (Image, video, and research credit: B. Steinfurth et al.)
Washing By Vortex Ring
Spraying a surface clean with a jet of fluid can be an energy-intensive operation. But a recent experiment shows that pulsed flow — which creates vortex rings — could be a viable cleaning alternative. Here we see vortex rings impacting a porous, beaded surface that’s covered in oil. Vortex rings with lots of rotation actually pass through the beads, knocking oil off both the front and back surfaces (Image 1). Even with a lower rotation rate, a vortex ring can still help clean the upper surface (Image 2). (Image and research credit: S. Jain et al.; via APS Physics)
Turbulence From Vortex Rings
When vortex rings collide, they reconnect into smaller, rings that eventually break down into chaos. Here, researchers experiment with colliding multiple vortex rings — focusing on an eight-ring collision. When they collide rings over and over, it creates a zone of isolated turbulence at the heart of the collisions.
Many of the theories and predictions that exist around turbulence assume that the flow is homogeneous and isotropic; what this means is that the (statistical) characteristics of the flow are the same in every direction. In reality, this kind of flow isn’t always easily achieved, which makes testing theoretical predictions challenging.
What’s neat about this set-up is that you get this desired turbulence in a very controlled way. It’s easy to tune the size and energy of your vortex rings, and those tweaks allow you to observe what — if any — changes occur in the resulting turbulence. (Image and video credit: T. Matsuzawa et al.)
“Reconfiguring It Out”
Leaves flutter and bend in the breeze, changing their shape in response to the flow. Here, researchers investigate this behavior using flexible disks pulled through water. The more flexible the disk and the faster the flow, the more cup-like the disk’s final shape. Adding tracer particles to the water allows them to visualize the flow behind the disk. Every disk leaves a donut-shaped vortex ring spinning in its wake, but the more reconfigured the disk, the narrower the vortex. This, ultimately, reduces drag on the disk. That’s why trees in heavy winds streamline their branches and leaves; that flexibility lowers the drag the tree’s roots have to anchor against. (Image and video credit: M. Baskaran et al.)
Dolphins Playing With Bubble Rings
Blow a jet of air underwater and you can make a bubble ring. It takes some practice for humans, or you can use a device. In this video, a team introduced wild dolphins to a bubble-ring-making machine and observed how the dolphins reacted. After some initial wariness, the animals played with them for hours, creating games and having fun. Note that there are some dolphins who create their own bubble rings to play with, so it’s hard to say that these particular dolphins have never seen a bubble ring before. But even if they have seen the bubbles, they wouldn’t have seen a machine making them. (Image and video credit: BBC Earth)
Underwater Explosions and Submarines
In the early days of submarines, it did not take physicists and engineers long to discover how destructive underwater explosions can be. In this Slow Mo Guys video, Gav gives us a glimpse of that destruction using a model submarine in a fish tank and several small explosives. You’ll have to be quick to notice the initial shock waves that ripple through the tank, but the footage captures spectacular detail on some of the slower-moving phenomena. You can see the uneven ripples of the explosion bubble’s surface as it expands. There are some great shots from the front and side showing the bubbly vortex ring that forms when the explosion hits the side of the tank wall (something that wouldn’t happen out in the ocean, of course). You can even catch a glimpse of some unexploded powder streaking out of the explosion. (Image and video credit: The Slow Mo Guys)
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