Zesting the skin of a citrus fruit like oranges releases a spray of tiny oil droplets. Citrus oil has several volatile components, meaning that it evaporates quickly at room temperature. It is also a liquid with a relatively low flash point, meaning that only modest temperatures (~40-60 degrees Celsius) are needed to generate enough vapor to ignite a vapor/air mixture. With volatile and flammable liquid fuels, a spray of droplets is an ideal platform for combustion because the essentially spherical droplets have a high surface area from which they can evaporate and provide vaporous fuel. (Video credit: ChefSteps)
Category: Art
Hovering
Designer Eleanor Lutz used high-speed video of five different flying species to create this graphic illustrating the curves swept out in their wingbeats. The curves are constructed from 15 points per wingbeat and are intended more as art than science, but they’re a fantastic visualization of several important concepts in flapping flight. For example, note the directionality of the curves as a whole. If you imagine a vector perpendicular to the wing curves, you’ll notice that the bat, goose, and dragonfly would all have vectors pointing forward and slightly upward. In contrast, the moth and hummingbird would have vectors pointing almost entirely upward. This is because the moth and hummingbird are hovering, so their wing strokes are oriented so that the force produced balances their weight. The bat, goose, and dragonfly are all engaged in forward flight, so the aerodynamic force they generate is directed to counter their weight and to provide thrust. (Image credit: E. Lutz; via io9)
Freediving
The freediving del Rosario brothers have created a real treat with this underwater film. There are no computer-generated special effects, just some clever tricks with camera angles, perspective, and buoyancy. The end result is slightly surrealistic and captures some of the fluid beauty of the ocean. And don’t miss the excellent bubble ring vortices. (Video credit: The Ocean Brothers; via Gizmodo; submitted by jshoer)
“Smoke”
Ethereal forms shift and swirl in photographer Thomas Herbich’s series “Smoke”. The cigarette smoke in the images is a buoyant plume. As it rises, the smoke is sheared and shaped by its passage through the ambient air. What begins as a laminar plume is quickly disturbed, rolling up into vortices shaped like the scroll on the end of a violin. The vortices are a precursor to the turbulence that follows, mixing the smoke and ambient air so effectively that the smoke diffuses into invisibility. To see the full series, see Herbich’s website. (Image credits: T. Herbich; via Colossal; submitted by @jchawner, @__pj, and Larry B)
P.S. – FYFD now has a page listing all entries by topic, which should make it easier for everyone to find specific topics of interest. Check it out!
Hydrophobicity and Viscous Flow
Hydrophobic surfaces are great for creating some wild behaviors with water droplets, but they make neat effects with other liquids, too. The viscous honey in the first segment of this Chemical Bouillon video is a great example. Because the honey doesn’t adhere to the hydrophobic surface, the viscoelastic fluid does not maintain the form it had when drizzled on the surface. Instead, the honey contracts, with surface tension driving Plateau-Rayleigh-like instabilities that break the contracting ligaments apart to form nearly spherical droplets of honey on the surface. (Video credit: Chemical Bouillon)
Paint on Speakers
Paint seems to dance and leap when vibrated on a speaker. Propelled upward, the liquid stretches into thin sheets and thicker ligaments until surface tension can no longer hold the the fluid together and droplets erupt from the fountain. Often paints are shear-thinning, non-Newtonian fluids, meaning that their ability to resist deformation decreases as they are deformed. This behavior allows them to flow freely off a brush but then remain without running after application. In the context of vibration, though, shear-thinning properties cause the paint to jump and leap more readily. For more images, see photographer Linden Gledhill’s website. (Photo credit: L. Gledhill; submitted by pinfire)
“The Flow II”
“The Flow II” film by Bose Collins and colleagues features a ferrofluid, a magnetically-sensitive liquid made up of a carrier fluid like oil and many tiny, ferrous nanoparticles. Although ferrofluids are known for many strange behaviors, their most distinctive one is the spiky appearance they take on when exposed to a constant magnetic field. This peak-and-valley structure is known as the normal-field instability. It’s the result of the fluid attempting to follow the magnetic field lines upward. Gravity and surface tension oppose this magnetic force, allowing the fluid to be drawn upward only so far until all three forces balance. (Video credit: B. Collins et al.)
“Clourant”
Photographers Cassandra Warner and Jeremy Floto produced the “Clourant” series of high-speed photographs of colorful liquid splashes. The artists took special care to disguise the origin of splashes, making them appear like frozen sculptures. The photos are beautiful examples of making fluid effects and instabilities. Many of them feature thin liquid sheets with thicker rims just developing ligaments. In other spots, surface tension has been wholly overcome by momentum’s effects and what was once ligaments has exploded into a spray of droplets. (Photo credit: C. Warner and J. Floto; submitted by jshoer; via Colossal)
“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)
Abstract Fluids
Janet Waters’ abstract photography is full of effects created with fluid dynamics. Diffusion merges different fluids, and gradients in surface tension drive interfacial flows. Changes in density and viscosity produce fingers and streaks and all manner of forms. Be sure to check out her photostream for many more examples of fluids as art. (Photo credits: J. Waters)
