Here’s an example of some baffling fluid dynamics. Researchers have found that, when pouring a fluid from one container into a lower one containing a fluid with floating particulates, it’s possible for the floating particles to travel upstream against gravity and the flow. The phenomenon is driven by surface tension. The particulates floating in the lower container decrease the fluid’s surface tension relative to the pure fluid pouring in from above. This creates a gradient in surface tension that, via the Marangoni effect, drives a small flow upstream, in the direction of the greater surface tension. In the video above, this flow takes the form of two recirculating vortices in the pouring channel, oriented such that their upstream velocities run along the outside of the channel. Occasionally this flow draws particulates up the waterfall and into the recirculating zones, creating upstream contamination. We reported this previously, but the researchers have now released videos demonstrating the effect, including in pipettes and a water flume. Usually it’s taken for granted that matter cannot move upstream, so this could be a game-changer, especially at small scales where surface tension already dominates. For more, see their paper. (Video credit: S. Bianchini et al.)
Search results for: “art”
Bouncing in Lockstep
Droplets of silicone oil bounce on a pool of the same thanks to the vibration provided by a loudspeaker. Each droplet’s bounce causes ripples in the pool and the interference between these ripples fixes the droplets in lockstep with one another. As long as the vibration continues to feed the thin layer of air that separates the droplets from the pool during each bounce and no impurities break the surface tension at the interface, the droplets will bounce indefinitely on their liquid trampoline. Such systems can be used to observe quantum-mechanical behavior like wave-particle duality on a macro-scale. (Photo credit: A. Labuda and J. Belina)
Flow Over a Delta Wing
Fluorescent dye illuminated by laser light shows the formation and structure of vortices on a delta wing. A vortex rolls up along each leading edge, helping to generate lift on the triangular wing. As the vortices leave the wing, their structure becomes even more complicated, full of lacy wisps of vorticity that interact. Note how, by the right side of the photo, the vortices are beginning to draw closer together. This is an early part of the large-wavelength Crow instability. Much further downstream, the two vortices will reconnect and break down into a series of large rings. (Photo credit: G. Miller and C. Williamson)
Self-Assembling Ferrofluids
Ferrofluids–colloidal suspensions made up of ferromagnetic nanoparticles and a carrier liquid–are known for their interesting and sometimes bizarre behaviors due to magnetic fields. The video above shows how, when subjected to an increasing magnetic field, a single droplet of a ferrofluid on a superhydrophobic surface will split into several droplets. The process is called static self-assembly, and it results from the ferrofluid seeking a minimum energy state relative to the force supplied by the magnetic field. Change the magnetic field and the droplets shift to the next energy minimum. But what happens when you change the magnetic field continuously and too quickly for the droplets to respond? A whole different set of structures and behaviors are observed (video link). This is dynamic self-assembly, a different ordered state only achieved when the ferrofluid is forceably kept away from the energy minima seen in the first video. For more, see the additional videos and the original paper. (Video credit: J. Timonen et al.; via io9)
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)
Brownian Motion
Have you ever noticed how motes of dust seem to dance around even in still air? The reason they do is because all the atoms and molecules in the air have a certain amount of random motion and all those tiny random motions result in collisions on the dust particles that shift them around. The technical term for this is Brownian motion, named for botanist Robert Brown who noticed through his microscope that particles of pollen floating on water moved constantly under no apparent force. The video above demonstrates the effect in 2D with vibrating brass particles representing atoms and a polystyrene ball as the pollen. Alternatively, you can see Brownian motion in the movement of nanoparticles in water. Although most areas of fluid dynamics do not explicitly consider the random motions of all these particles, the concept is fundamental to the nature of pressure and temperature, both of which are important quantities in fluid dynamics. (Video credit: Sixty Symbols; topic requested by just-a-random-nerd)
“Liquid Jewel”
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Today’s image is from artist Fabian Oefner’s “Liquid Jewel” series, featuring paint-filled balloons moments after rupture. Oefner has several series displaying physical forces as visual media, including the previously featured “Black Hole” and “Millefiori” photos. (Photo credit: F. Oefner)
Bursting Bubble
Originally posted: 24 Aug 2011 That soap bubbles burst in the blink of an eye is a pity considering how fascinating their disappearing act is. This photo set from photographer Richard Heeks captures the bubbles mid-burst. Once the bubble’s film is breached, surface tension rips the smooth film back like a broken balloon, causing the liquid that used to be part of the bubble to erupt into droplets. (Photo credit: Richard Heeks)
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Soap Film Butterfly
Originally posted: 14 Jan 2011 This gorgeous butterfly-like double spiral roll takes place on a horizontal soap film. The foil (seen top center) inserted in the film flaps back and forth. Each time the foil changes direction a vortex forms at the tip and gets advected away. The vortices stretch and distort in the roll, but if you look at the photograph closely, you’ll see the tiny shed vortices persisting throughout the roll structure. The bright colors that make this flow visible are due to interference patterns related to the local thickness of the film. (Photo credit: T. Schnipper et al.)
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Rocket Sonic Boom
Originally posted: 22 July 2010 This video of the NASA Solar Dynamics Observatory’s launch is such a favorite of mine that it was part of the original inspiration for FYFD and was the very first video I posted. Watch closely as the Atlas V rocket climbs. At 1:51 you’ll see a rainbow-like cloud in upper right corner of the screen. This effect is created by sunlight shining through ice crystals of the cloud. A couple seconds later you see pressure waves from the rocket propagate outward and destroy the rainbow effect by re-aligning the ice crystals. Just after that comes the announcement that the vehicle has gone supersonic. The atmospheric conditions of the launch happened to be just right to make those pressure waves coming off the rocket visible just before they coalesced into a leading shockwave. (Video credit: B. Tomlinson)
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