We’ve touched on volcanoes and the fluid dynamics of lava a couple of times here at FYFD, but over at Wired volcanologist Erik Klemetti has some wonderful photos and videos he took while visiting an active lava flow in Hawaii along with great explanations of the flow shapes and processes. Above we see him using a rock hammer to remove a sample from an active flow. Klemetti describes the lava’s behavior as taffy-like – extremely viscous and stretchy but prone to break like a plastic. Be sure to check out his posts! (Photo credit: E. Klemetti; submitted by @FlexMonkey)
Tag: science
Colorful Spirals
Artist Fabian Oefner captures these colorful portraits of fluid instability by dripping acrylic paints onto a metal rod, which is connected to a drill. When the drill is switched on, paint is flung away from the rod, creating these snapshots of centripetal force and surface tension. Note how droplets gather at the ends of the spiral arms like in a Plateau-Rayleigh or a rimming instability. For more, check out Oefner’s webpage, which includes a video showing how the images are made, or his previously featured work, “Millefiori”. (Photo credit: F. Oefner; submitted by Stephen D.)
Mixing the Southern Ocean
Motion in the ocean is driven by many factors, including temperature, salinity, geography, and atmospheric interactions. While global currents dictate much of the large-scale motion, it’s sometimes the smaller scales that impact the climate. This visualization shows numerically simulated data from the Southern Ocean over the course of a year. The eddies that swirl off from the main currents are responsible for much of the mixing that occurs between areas of different temperature, which ultimately impacts large-scale temperature distributions, in this case affecting the flux of heat toward Antarctica. (Video credit: I. Rosso, A. Klocker, A. Hogg, S. Ramsden; submitted by S. Ramsden)
Lift on a Paper Plane
In this still image from a student experiment, smoke visualization shows the formation of a vortex over the wing of a paper airplane during a wind tunnel test. This wing vortex is mirrored on the opposite wing, though there is no smoke to show it. At high angle of attack, the delta-wing shape of the traditional paper air plane creates these vortices on the upper surface, which helps generate the lift necessary to keep the plane aloft. (Photo credit: A. Lindholdt, R. Frausing, C. Rechter, and S. Rytman)
Mixing While Laminar
Although turbulent flows are known for their mixing efficiency, in manufacturing there can often be a need to mix laminar fluid streams without the increased shear stress of a turbulent flow. This can be particularly important for polymeric liquids, where too much shear stress could damage the polymer chains. One possibility is using a static mixer, such as the one demonstrated in this video, which, when placed in pipe flow, will deflect the pipe’s contents in such a way as to produce efficient mixing over a short distance. Here two streams of high-viscosity epoxy are mixed through such a static mixer, hardened, and then ground to show the mixing at each level of the static mixer. (Video credit: Sulzer)
The Boundary Layer Visualized
Any time there is relative motion between a solid and a fluid, a small region near the surface will see a large change in velocity. This region, shown with smoke in the image above, is called the boundary layer. Here air flows from right to left over a spinning spheroid. At first, the boundary layer is laminar, its flow smooth and orderly. But tiny disturbances get into the boundary layer and one of them begins to grow. This disturbance ultimately causes the evenly spaced vortices we see wrapping around the mid-section of the model. These vortices themselves become unstable a short distance later, growing wavy before breaking down into complete turbulence. (Photo credit: Y. Kohama)
Under the Waves
When I was a kid, I liked to dive underwater in the pool and sit at the bottom, looking up at the peculiar dancing sky the water made overhead. Photographer Mark Tipple takes it further, capturing images of the ocean from below the surface as waves roll in. His photos show swimmers and surfers diving to escape a roiling wave that, from below, bears a surreal similarity to the underside of a thundercloud in a summer storm. This is part of the beauty of fluid dynamics. Despite their differences, water and air obey the same physics. (Photo credits: Mark Tipple; via io9)
Frozen Methane Bubbles
As the Arctic warms, methane that was previously trapped by permafrost rises from the muddy bottom of lakes to escape into the atmosphere. Here the first clear ice of the fall has trapped the rising methane bubbles, allowing scientists an opportunity to estimate the amount of methane being released. When spring arrives and the lakes melt, the methane will rise again. (Photo credit: M. Thiessen/National Geographic)
“Frozen” Water Stream
We saw previously how vibrating a falling stream of water and filming it with a matching camera frame rate appears to “freeze” the falling liquid. This video shows the same illusion, now with a 24 Hz sine wave, which the falling water mimics. Vibrating the speaker that drives the water stream slightly slower or slightly faster than the camera frame rate makes the water appear to slowly fall or rise relative to its “frozen” wave state. This is a beat effect caused by the slight difference in frequency between the water and the camera. (Video credit: brusspup; via BoingBoing; submitted by many readers)
Inside a Blender
The fluid dynamics of a commercial-quality blender amount to a lot more than just stirring. Here high-speed video shows how the blender’s moving blades create a suction effect that pulls contents down through the middle of the blender, then flings them outward. This motion creates large shear stresses, which help break up the food, as well as turbulence that can mix it. But if you watch carefully, you’ll also see tiny bubbles spinning off the blades. These bubbles, formed by the pressure drop of fluid accelerated over the arms of the blades, are cavitation bubbles. When they collapse, or implode, they create localized shock waves that further break up the blender’s contents. This same effect is responsible for damage to boat propellers and lets you destroy glass bottles. (Video credit: ChefSteps; via Wired; submitted by jshoer)
