Rocky islands make excellent atmospheric swirls, as seen here around Guadalupe Island. Winds blowing in from the ocean get forced up and around the island’s topography, resulting in vortices that shed alternately from either side of the island. The pattern they form is known as a von Karman vortex street and is easily seen in satellite imagery, thanks to the swirls that can persist for tens of kilometers downstream. Personally, I never get tired of this one! (Image credit: NASA/GSFC/JPL; video credit: NOAA/CIRA; via Dakota Smith; submitted by @SellaTheChemist)
Search results for: “vortex”
A Colorful Fire Tornado
This one definitely belongs in the do-not-try-this-yourself category, but this Slow Mo Guys video of a colorful fire tornado is pretty spectacular. Using an array of different fuels and a ring of box fans, Gav sets up a vortex of flame that transitions smoothly from red all the way to blue. As he points out in the video, the translucency of the vortex is so good that you can see how the two sides of the vortex rotate! (Video credit: The Slow Mo Guys)
The Bubbly Escape
Sometimes experiments don’t work as planned and, instead of answers, they lead to more questions. In this video, we see an experiment looking at an air bubble trapped beneath a cone. It’s the same situation you get by holding a mug upside-down in a sink full of water but with inclined walls. As the cone moves downward, it squeezes the trapped air bubble. A film of air gets pushed along the walls of the cone, eventually forming finger-like bubbles that wrap around the edge of the cone and get entrained into the vortex ring outside the cone.
Clearly, there is some kind of instability that drives the air bubble to form these fingers rather than spreading uniformly. But the big question is which one? Is this a density-driven Rayleigh-Taylor instability caused by air getting pushed into water? Or is it a Saffman-Taylor instability causes by the less viscous air forcing its way into the more viscous water? What do you think? (Image and submission credit: U. Jain)
Devising Greener Chemistry
Not all microfluidic devices use tiny channels to pump and mix fluids. Some, like the Vortex Fluidic Device (VFD), conduct their microfluidic mixing in thin films of fluid. The VFD is essentially a tube spinning at several thousand RPM that can be tilted to various angles. Coriolis forces, shear, and Faraday instabilities in the thin fluid film create a complex microfluidic flow field that’s excellent for mixing, crystallization, and processing of injected chemicals. One rather notorious application of this device was unboiling an egg, a feat for which the researchers won an Ig Nobel Prize. But other, more practical applications abound, including a waste-free method for coating particles. (Image and research credit: T. Alharbi et al.; video credit: Flinders University; via Cosmos; submitted by Marc A.)
Space Hurricanes
Researchers have observed their first “space hurricane” – a 1,000-km-wide vortex of plasma – in Earth’s upper atmosphere. Like conventional hurricanes, this storm featured precipitation (of electrons rather than rain), a calm eye at its center, and several spiral arms. Based on the group’s model, interactions between the solar wind and Earth’s magnetic fields drive the storm. Interestingly, the storm they observed occurred during a period of low solar and geomagnetic activity, which suggests that such space hurricanes could be frequent, both on Earth and in the upper atmospheres of other planets. (Image credit: Q. Zhang; research credit: Q. Zhang et al.; via Physics World)
Jovian Auroras
Like Earth, Jupiter is home to polar auroras that light the sky as charged particles interact with the planet’s magnetosphere. A recent paper identifies interesting features in the aurora that appear similar to expanding vortex rings (see inset below). Although the researchers cannot yet identify the origin of the rings, they hypothesize that the process begins at the far edges of Jupiter’s magnetosphere where it interacts with the incoming solar wind. One theory posits that shear flows and Kelvin-Helmholtz instabilities where the magnetosphere and solar wind meet drive the phenomenon. (Image credit: Jupiter – NASA, ESA, and J. Nichols, aurora features – NASA/SWRI/JPL-Caltech/SwRI/V. Hue/G. R. Gladstone/B. Bonfond; research credit: V. Hue et al.; via Gizmodo)
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)
Jellyfish Make Their Own Walls
When we walk, the ground’s resistance helps propel us. Similarly, flying or swimming near a surface is easier due to ground effect. Most of the time swimmers don’t get that extra help, but a new study shows that jellyfish create their own walls to get that boost.
Of course, these walls aren’t literal, but fluid dynamically speaking, they are equivalent. Over the course of its stroke, the jellyfish creates two vortices, each with opposite rotation. One of these, the stopping vortex, lingers beneath the jellyfish until the next stroke’s starting vortex collides with it. When two vortices of equal strength and opposite rotation meet, the flow between them stagnates — it comes to halt — just as if a wall were there.
In fact, mathematically, this is how scientists represent a wall: as the stagnation line between a real vortex and a virtual one of equal strength and opposite rotation. It just turns out that jellyfish use the same trick to make virtual walls they can push off! (Image and research credit: B. Gemmell et al.; via NYTimes; submitted by Kam-Yung Soh)
Strings of Swirls
Von Karman vortex streets are the rows of alternating vortices shed off isolated objects interrupting a flow. Here, the volcanic peaks of Cabo Verde disrupt an atmospheric flow accustomed to an empty ocean. In a steady wind, air wraps around the volcanoes and detaches first on one side, creating a vortex, then from the other side, making a vortex of the opposite rotation. Although these structures are always present, we only see them when they stir up the cloud layer, leaving these strings of swirls for hundreds of kilometers behind the islands. (Image credit: L. Dauphin/NASA; via NASA Earth Observatory)
High Tide
Broad Sound, in eastern Australia, is home to some of the most extreme tidal swings in the world, with more than ten meters difference between high and low tides. The bay’s peculiar geography, along with the topography of nearby reefs, combine to cause the large tides. This color-enhanced satellite image shows the bay at high tide, as phytoplankton and suspended sediments are swept into the bay and around its many islands. The level of detail is just stunning. I particularly love all the von Karman vortex streets visible in the wakes of islands. I count more than a dozen of them! (Image credit: N. Kuring/NASA/USGS; via NASA Earth Observatory)
