What’s this? An FYFD video?! Yes, at long last, I’ve begun filming some videos of my own. This first one takes a look at the Rayleigh-Taylor instability and all that action that goes on in your coffee cup. I hope to bring you more FYFD-produced videos in the future, including some videos from the American Physical Society Division of Fluid Dynamics conference in San Francisco next week. What kind of topics would you guys be interested in for the future? (Video credit: N. Sharp)
Tag: Rayleigh-Taylor instability
Supernova Simulation
New research shows that supermassive first-generation stars may explode in supernovae without leaving behind remnants like black holes. The work is a result of modeling the life and death of stars 55,000 to 56,000 times more massive than our sun. When such stars reach the end of their lives, they become unstable due to relativistic effects and begin to collapse inward. The collapse reinvigorates fusion inside the star and it begins to rapidly fuse heavier elements like oxygen, magnesium, or even iron from the helium in its core. Eventually, the energy released overcomes the binding energy of the star and it explodes outward as a supernova. The image above is a slice through such a star approximately one day after its collapse is reversed. Hydrodynamic instabilities like the Rayleigh-Taylor instability produce mixing of the heavy elements throughout the expanding interior of the star. The mixing should produce a signature that can be observed in the aftermath as these stars seed their galaxies with the heavy elements needed to form planets. For more, see Science Daily and Chen et al. (Image credit: K. Chen et al., via Science Daily; submitted by mechanicoolest)
“Chromatic Mushrooms”
Chemical Bouillon’s art often mixes chemistry and fluid dynamics. Here dense UV dyes falling through a less dense fluid form long strings with mushroom-like caps or tree-like branches. (For reference, gravity is pointing up relative to the video frame in most clips.) This behavior is related to the Rayleigh-Taylor instability that deforms interfaces and causes mixing between unstably stratified fluids. (Video credit: Chemical Bouillon)
“Demersal”
The ethereal shapes of inks and paints falling through water make fascinating subjects. Here the ink appears to rise because the photographs are upside-down. The fluid forms mushroom-like plumes and little vortex rings. The strands that split apart into tiny lace-like fingers are an example of the Rayleigh-Taylor instability, which occurs when a denser fluid sinks into a less dense one. Similar fingering can occur on much grander scales, as well, like in the Crab Nebula. These images come from photographer Luka Klikovac’s “Demersal” series. (Photo credit: L. Klikovac)
Explosive Boiling
A superheated liquid can reach temperatures higher than its boiling point without actually boiling – similar to how liquids can be supercooled below their freezing point without solidifying. The photo sequence above shows how explosive the boiling of a superheated water droplet submersed in sunflower oil can be. Image (a) in the lower left shows the superheated droplet resting on the bottom of its container. Then droplet vaporizes explosively in (b), expanding dramatically. The bubble overexpands and and begins to oscillate around its equilibrium radius. This triggers a Rayleigh-Taylor instability in the bubble’s interface, creating the large lobes in © and enlarged in the upper image. Finally, the bubble fragments in (d). See the original paper for more on superheated droplet boiling. (Image credit: M. A. J. van Limbeek et al.; via @AIP_Publishing)
Ink Diffusion
Alberto Seveso’s gorgeous high-speed photos of ink diffusing in water have a dramatic sense of texture to them. Though still delicate, the whorls of fluid seem almost solid enough to touch. Watch the edges, though, and you can see thin wisps of color and hints of instabilities. Like cream poured into coffee, these ink sculptures are short-lived. Some of his works are available as prints or wallpapers (zip file). (Photo credit: Alberto Seveso)
Instability: Dense Over Light
Here on Earth, placing a dense layer of fluid atop a less dense layer is unstable. Specifically, the situation causes the interface between the two fluids to break down in what is known as the Rayleigh-Taylor instability.The video above shows a 2D numerical simulation of this breakdown, with the darker, denser fluid on top. The waviness of the initial interface provides a perturbation–a small disturbance–which grows in time. The two fluids spiral into one another in a fractal-like mushroom pattern. The continued motion of the dense fluid downward and the lighter fluid upward mixes the entire volume toward a uniform equilibrium. For those interested in the numerical methods used, check out the original video page. (Video credit: Thunabrain)
Liquid Sculptures
Artist Corrie White uses dyes and droplets to capture fantastical liquid sculptures at high-speed. The mushroom-like upper half of this photo is formed when the rebounding jet from one droplet’s impact on the water is hit by a well-timed second droplet, creating the splash’s umbrella. In the lower half of the picture, we see the remains of previous droplets, mixing and diffusing into the water via the Rayleigh-Taylor instability caused by their slight difference in density relative to the water. There’s also a hint of a vortex ring, likely from the droplet that caused the rebounding jet. (Photo credit: Corrie White)
Ink Drops
This super high resolution video (check the original on YouTube) by filmmaker Jacob Schwarz features slow motion diffusion of ink into water. The subtle differences in density between the ink and the water promote instabilities such as the Rayleigh-Taylor instability and its distinctive cascade of mushroom- or umbrella-like shapes. The mixing of two fluids seems like a simple concept, but the reality is beautiful, complex, and always fascinating. (Video credit: J. Schwarz; submitted by Rebecca S.)
Dropping Through Strata
When a droplet falls through an air/water interface, a vortex ring can form and fall through the liquid. In this video, the researchers investigate the effects of a stratified fluid interface on this falling vortex ring. In this case, a less dense fluid sits atop a denser one. Depending on the density of the initial falling droplet and the distance it travels through the first fluid, the behavior and break-up of the vortex ring when it hits the denser fluid differs. Here four different behaviors are demonstrated, including bouncing and trapping of the vortex ring. (Video credit: R. Camassa et al.)
