File this one under awesome tricks you shouldn’t try at home. Here bubble artist Dustin Skye demonstrates his handheld inverted fire tornado. First, he blows a large encapsulating bubble, then blows butane and smoke into a smaller secondary bubble. When he breaks the wall between the two, the mixture swirls into the larger bubble. Then, by breaking a narrow hole into the remaining bubble, Skye forms a swirling tornado. He’s using conservation of angular momentum here to concentrate the vorticity he created by blowing into the original butane bubble. As the big bubble shrinks, the vorticity inside gets pulled inward and speeds up – like when a spinning ice skater pulls his arms in. That’s how you get the tornado. And from there, it’s just a matter of lighting the exiting butane and air mixture. (Video credit: D. Skye; via Gizmodo)
Search results for: “vorticity”
Fighting a Viscous World
Vaucheria is a genus of yellow-green algae (think pond scum), and some species within this genus reproduce asexually by releasing zoospores. Once mature, the zoospore has to squeeze out of a narrow, hollow filament in order to escape into the surrounding fluid (top). To do so, it uses tiny hair-like flagella on its surface. Despite the minuscule size of these micron-length flagella, they generate some major flows around the zoospore (middle and bottom). Even several body lengths away, the flow field shows significant vorticity. All this active entrainment of fluid from the surroundings helps the zoospore escape its confinement and swim away to start a new plant. (Image and research credit: J. Urzay et al., source)
From Firenado to Water Spout
Just a few years ago, fire tornadoes were almost fabled because they were so rarely captured on video. Now, with worsening wildfire seasons and cell phone cameras everywhere, there are new videos all the time. This video captures a fire tornado that sets off a water spout as it reaches the river (~1:15 in).
Neither the fire tornado or the water spout is truly tornadic; instead they are more like dust devils. They are driven by the rising heat of the fire. As cooler, ambient air flows inward to replace the rising air, it brings with it any vorticity it had. And, like an ice skater, the incoming air spins faster as it moves inward. This sets up both the fire tornado and the water spout’s vortices.
Although this is the first example I’ve seen video of, fire tornadoes have been known to create water spouts before. Lava flowing into the ocean can create whole trains of them. (Video credit: C. & A. Mackie; via Jean H.)
Caught in a Whirl
Vortex rings may look relatively calm, but they are concentrated regions of intensely spinning flow, as this poor jellyfish demonstrates. The rings form when a high-speed fluid gets pushed suddenly (and briefly) into a slower fluid. In the case of this bubble ring, a burst of air is pushed by a diver into relatively still water. The vorticity caused by the two areas of fluid trying to move past one another forms the ring. Like a spinning ice skater who pulls his arms inward, the narrow core of the vortex spins fast due to the conservation of angular momentum. Meanwhile, the bubble ring moves upward due to its buoyancy, pulling nearby water in as it goes. This catches the hapless jellyfish (who relies on vortex rings itself) and gives it quite a spin. But. don’t worry, the photographer confirmed that the jelly was okay after its ride. (Video credit: V. de Valles; via Ashlyn N.)
In the Eye of a Hurricane
Although eyes are common at the center of large-scale cyclones, scientists are only now beginning to understand how they form. Since real-world cyclogenesis is complicated by many competing effects, researchers look at simplified model systems first. A typical one uses a shallow, rotating cylindrical domain in which heat rises from below. The rotation provides a Coriolis force, which shapes the flow. In particular, it causes a boundary layer along the lower surface of the domain, creating a thin region where the flow moves radially inward. (Its opposite forms at the upper surface of the domain, sending flow radiating outward.) Like an ice skater spinning, the flow’s vorticity intensifies as it approaches the central axis of rotation. When the conditions are right, this intensely swirling boundary layer flow lifts up into the main flow, forming an eyewall. The eye itself, it turns out, is merely a reaction to the eyewall’s formation. (Image credit: S. Cristoforetti/ESA; research credit: L. Oruba et al.)
“Catacomb of Veils”
Burning Man’s “Catacomb of Veils”, the largest sculpture burned in the 2016 event, produced a series of smoke tornadoes as it blazed. Like dust devils or fire tornadoes, these vortices are driven by hot, buoyant air rising – in this case, from the fire. As the surrounding air moves in toward the fire, any rotational motion, or vorticity, in the air is intensified due to conservation of angular momentum. That concentrates it into a vortex, which becomes visible when it picks up smoke. Simultaneously, the wind was blowing in a consistent direction, sending any new vortices generated marching downstream. You can watch even more vortices and some slow-motion footage of the burning in the full video by Mark Day. (Image credit: M. Day, source; submitted by Larry B)
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)
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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Fire Tornado
Fire tornadoes, despite their name, are more like dust devils than your typical tornado. In nature, they’ll often form in wildfires, but here the Slow Mo Guys simulate one for the high-speed cameras using a ring of box fans set up to provide rotational flow, or vorticity, around a kerosene fire. As the fire burns, the warm air over the flame moves upward due to buoyancy. This creates a low-pressure area around the fire that draws in the spinning air from further out. Like an ice skater who pulls her arms in when spinning, the rotating air spins faster as it moves in toward the fire, resulting in a swirling turbulent vortex of flame. Hopefully it goes without saying, but, seriously, don’t try this at home. (Video credit: Slow Mo Guys; submitted by Chris S.)