FYFD

Tag: flow visualization

  • Understanding Jupiter

    Understanding Jupiter

    The swirling clouds of Jupiter hide a complicated and mysterious interior. For decades, scientists have worked to puzzle out the inner dynamics of Jupiter’s atmosphere and what could be going on inside it to generate the flows we see visibly. Near Jupiter’s equator, we see strong jets that flow either east or west, depending on their latitude; this creates the stunning cloud bands we’re used to seeing on the planet. Toward the poles, though, things look more like what we see above – swirling but unbanded.

    Through theory, experiments, and simulations, scientists have tried to work out exactly what ingredients are necessary to make Jupiter look this way, but it’s pretty tough to recreate the conditions simply because Jupiter is so extreme. You need a lot of rotation, a lot of turbulence, and a way to stretch that turbulence if you want to imitate Jupiter. There’s been progress recently, though, and it suggests that the jets we see on Jupiter are far more than skin-deep. Instead, they likely stretch deep into the Jovian atmosphere at the equator and ride somewhat shallower toward the poles. (Image credit: NASA JPL; research credit: S. Cabanes et al.)

  • Fighting a Viscous World

    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)

  • A Golden Swirl

    A Golden Swirl

    As much as I love exploring flashy examples of fluid dynamics, like shock waves around aircraft or what happens when non-Newtonain fluids get crushed by a hydraulic press, my favorite moments are the simple, everyday ones. Getting to see fluid dynamics in my daily life, whether I’m standing in the kitchen cooking or trying to wash my hands, is what excites me the most. The photo above is an example of this kind of simple, satisfying fluid experience. The image shows wax being melted in a crockpot. As it melts and its optical characteristics change, the wax reveals the mixing pattern inside the container. There’s nothing earth-shattering or scientifically important about something like this. But it’s still a moment where the otherwise unseen and unnoticed becomes visible and beautiful. It’s the fluid dynamical equivalent of stopping to smell the roses. When did you last pause to appreciate the flows around you? (Image credit: A. Unger et al.)

  • Blackwater Rivers

    Blackwater Rivers

    Blackwater rivers, like the Suwannee River in Florida, carry waters so laden with organic material that they’re dyed a deep, dark brown. For the Suwannee, most of this material comes from the rich peat deposits of the Okefenokee Swamp that lies upstream. As vegetation in the swamp decays, tannins from the plants dissolve into the water, giving it its distinctive color, which the river maintains along its full 400-kilometer journey to the Gulf of Mexico. The dark waters of the river act as a tracer, revealing how the fresh river water mixes with the ocean in the enhanced-color satellite image above. It’s amazing to see how far the river’s influence spreads before delicate wisps of color pierce the darkness. (Image credit: U.S. Geological Survey; via NASA Earth Observatory)

  • Vortex Dome

    Vortex Dome

    Are you staring into the eye of a hurricane or watching the spin of a simple desk toy? Part of the beauty of fluid dynamics is recognizing how similar they both are. This is high-speed footage of a toy known as a “Vortex Dome,” which contains a fluid filled with tiny mica particles that react to local forces and allow users to “see” the flow. Before the video begins, the toy has been spinning for long enough that the fluid inside rotates as if it were a solid body. Then an unseen hand sets the disk spinning in the opposite direction and we observe what happens.

    Fluid at the outer edge of the toy has to immediately change direction due to friction with the wall. That change in momentum slowly passes from the wall inward as viscosity between one layer of fluid to the next passes that signal. This creates the rolls we see in the first animation. Initially, those rolls are smooth, but they quickly roughen as disturbances in them grow into full-blown turbulence. Meanwhile, viscosity continues to pass the change in rotation inward, ultimately swallowing the entire interior of the toy. Left spinning indefinitely, the disturbances will eventually quiet out and the entire fluid will spin as one. (Image and video credit: D. van Gils)

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    An Introduction to Turbulence

    With some help from Physics Girl and her friends, Grant Sanderson at 3Blue1Brown has a nice video introduction to turbulence, complete with neat homemade laser-sheet illuminations of turbulent flows. Grant explains some of the basics of what turbulence is (and isn’t) and gives viewers a look at the equations that govern flow – as befits a mathematics channel! 

    There’s also an introduction to Kolmogorov’s theorem, which, to date, has been one of the most successful theoretical approaches to understanding turbulence. It describes how energy is passed from large eddies in the flow to smaller ones, and it’s been tested extensively in the nearly 80 years since its first appearance. Just how well the theory holds, and what situations it breaks down in, are still topics of active research and debate. (Video and image credit: G. Sanderson/3Blue1Brown; submitted by Maria-Isabel C.)

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    Making a Square Vortex

    As someone who has played with her share of vortex cannons, I can assure you that messing around with smoke generators and vortex rings is a lot of fun. And in this video, Dianna gives things a little twist: she makes the vortex cannon’s mouth a square instead of a circle.

    Now, that doesn’t create a square vortex ring. (Vortex rings don’t really do 90-degree corners.) But it does make the vortex ring all neat and wobbly. Whenever you have two vortices near one another (or, in this case, two parts of a vortex line near one another), they interact. As Dianna shows with hurricanes, depending on the direction of rotation and their relative strength, nearby vortices can orbit one another or travel together in straight lines – or they can cause more complicated interactions, like in the case of the square-launched rings.

    I think there may also be some interesting effects here from vortex stretching, but that’s a topic for another day! (Video and image credit: D. Cowern/Physics Girl; see also: LIBLAB; submitted by Maria-Isabel C.)

  • Solar Prominence

    Solar Prominence

    Near the surface of the sun, the interplay of magnetic fields and plasma flow creates solar prominences that appear to dance. The prominence shown here was recorded in 2012 by the NASA Solar Dynamics Observatory, and its arc is large enough to easily surround the Earth. This is fluid dynamics – specifically magnetohydrodynamics – on a scale difficult for us earthbound humans to imagine. Scientists are still working to understand the complex processes that drive flows like this one. Fortunately, we can appreciate their beauty regardless. (Image credit: NASA SDO, source; via APOD; submitted by jpshoer)

  • Swirls of Color

    Swirls of Color

    These beautiful swirls show the wake downstream of a thin plate. Here water is flowing from left to right and dye introduced on the plate (upstream and unseen in the photo) curls up into vortices. The vortices in the top row rotate clockwise, while the vortices along the bottom rotate anti-clockwise. This pattern of alternating vortices is extremely common in the wakes of objects and is known as a von Karman vortex street. Similar patterns are seen in soap films, behind cylinders, in the wakes of islands, and behind spaceships.  (Image credit: ONERA, archived here)

  • Stall with Pitching Foils

    Stall with Pitching Foils

    For a fixed-wing aircraft, stall – the point where airflow around the wing separates and lift is lost – is an enemy. It’s the precursor to a stomach-turning freefall for the airplane and its contents. But the story is rather different when the wing is actively pitching through these high angles of attack. In this case, you get what’s known as dynamic stall, illustrated in three consecutive snapshots above.

    In the top image, the flow has clearly separated from the upper surface of the wing, but this isn’t a cause for panic. As the middle image shows, there’s a vortex that’s formed in that separated region and it’s moving backward along the wing as the angle of attack continues to increase. That vortex causes a strong low-pressure region on the upper surface of the wing, allowing it to maintain lift.

    In the final image, the vortex is leaving the wing, taking its low-pressure zone with it. This is the point where the pitching wing loses its lift, but if the vortex’s departure is immediately followed by a pitch down to lower angles of attack, the aircraft will recover lift and carry on. (Image credit: S. Schreck and M. Robinson, source)