Readers may recall the University of Queensland’s pitch-drop experiment, recognized as the longest continuously running experiment in the world. Back in 1927, a professor started the experiment with the goal of measuring the extremely high viscosity of pitch. Since then, only eight drops have fallen. Queensland’s is not the only version of this experiment, though; Trinity College Dublin has a similar set-up and have just caught a falling pitch drop on camera for the first time ever. Take a look in the video above. Queensland is expecting a drop to fall sometime this year as well. (Video credit: Trinity College Dublin Physics; via SciAm)
Month: July 2013
Sedimentary Swirls
Local currents swirl sediments and phytoplankton blooms in this satellite image of the Tarut Bay in Saudi Arabia. Such blooms typically occur where nutrients are being washed together, thereby creating a kind of natural flow visualization of currents and matter flow in the ocean. (Photo credit: NASA Earth Observatory)
Foam Array
Soap foams represent an interplay of gravitational, capillary, interfacial, and viscous forces, none of which is easily isolated in a laboratory experiment. This makes it difficult to sort out the various effects governing the foam since individual variables cannot be controlled independently. The image above is of a special foam, one in which the liquid phase has been replaced with a ferrofluid. This adds an additional parameter–external magnetic fields–to the problem, but, unlike the others, this is an independent variable. By manipulating the external magnetic field, researchers can control the foam’s drainage rate and even the structure it takes on. (Photo credit: E. Janiaud)
Drop-Tower Droplets
A microgravity environment can cause some nonintuitive behaviors in fluids. Many of the effects that dominate fluid dynamics in space are masked by gravity’s effects here on Earth. As a result, it can be very difficult to predict how seemingly straightforward technologies like heat exchangers, refrigeration units, and fuel tanks will behave. The photos above show two bubble jets–created by injecting a liquid-gas mixture into a liquid–colliding in microgravity. This particular experiment was conducted in a drop tower rather than on-orbit, which produced some side effects like the large bubbles seen in the images. These were created by the coalescence of smaller bubbles that congregated near the top of the tank shortly before the experiment attained free-fall. (Photo credit: F. Sunol and R. Gonzalez-Cinca)
Levitation By Sound
Levitation is an effect usually associated with electromagnetic forces, but it’s possible with sound as well. This acoustic levitation is achieved by using the pressure from sound waves to balance gravity’s effect. By manipulating the sound, it’s possible to bring separate objects together while continuing to levitate them. The behavior is demonstrated in the video above by combining solid sodium with a drop of water for what any high school chemist will tell you is a spectacular reaction. (Though, if that’s too small-scale for you, there’s also this video.) (Video credit: D. Foresti et al; via SciAm)
Super-Highway Convection
In the ocean, many forces compete in driving convection, including the temperature and salinity of the water. In the laboratory, it’s possible to mimic these characteristics of oceanic circulation using two different fluids driven by temperature and concentration differences. Recently, researchers were exploring this problem–with the added twist of tilting the fluids ~1 degree–when they discovered a surprising result. After an extended time, the convection self-organized into alternating parallel columns of ascending (dark) and descending (light) fluid. The researchers nicknamed this behavior super-highway convection. Read more about it here or in their paper. (Video credit: F. Croccolo et al; submitted by A. Vailati)
Fluids Round-up – 13 July 2013
Prepare yourselves for lots of links in today’s fluids round-up!
- Longtime FYFD favorite Mark Stock (see here, here, and here) and his collaborator James Susinno have unveiled a new interactive art piece, “Everything is Made of Atoms” that utilizes some impressive real-time fluids simulation. NVIDIA’s blog has some details on the computing.
- ScarbsF1 takes a detailed look at the F-duct used to stall an F1 car’s rear wing to reduce drag. (submitted by Vinnie)
- Just in time for summer fun, National Geographic talks about the physics of water slides.
- SpaceX’s reusable Grasshopper rocket has set a new altitude test of over 1000 ft. Check out this feat of aerodynamic control over at io9.
- Stanford engineers are using high-speed video of birds in the wild to study the mechanics of flapping flight. If you check out their video, you’ll notice how the birds rotate their wings as they flap in order to maximize lift throughout the flapping cycle. (via io9)
- Speaking of io9, they highlighted a couple of great examples of meteorological fluid dynamics recently: roll clouds and water spouts.
- New research suggests that thresher sharks may whip their tails quickly enough to produce cavitation-induced shockwaves to stun their prey. If so, they join the pistol and mantis shrimp in utilizing this technique for hunting.
- If you’re looking for some casual games, Liquid Sketch is a fun fluids puzzle game for iOS (submitted by Keri B)
- Finally, congratulations to Toronoto’s AeroVelo for capturing the AHS Sikorsky Prize with their human-powered helicopter. Check out this video from their historic flight (submitted by Chris R).
(Photo credit: AeroVelo)
Fire-Breathing Physics
One of the most dangerous stunts for any fire-eater is breathing fire. Dr. Tim Cockerill explains some of the science behind the feat in this video. Volatility–the tendency of the liquid fuel to vaporize–is actually the enemy of a fire-eater. Use a fuel that is too volatile and it will catch fire too easily when the vaporous fuel mixes with the air. Instead fire-eaters use less volatile fuels and spray a mist of fine droplets to mix the air and fuel. This atomization of the fuel creates a spectacular fireball without endangering the fire-eater (as much). To see a similar fireball in high-speed, check out this post. (Video credit: T. Cockerill/The Ri Channel; via io9)
Flow Around a Complex Airfoil
Flow around an airfoil with a leading-edge slat is visualized above. At this Reynolds number, alternating periodic vortices are shed in its wake. Understanding how multi-element airfoils and control surfaces affect local flow is important in controlling aircraft aerodynamics. When multiple instabilities interact–like those in the wing’s boundary layer interacting with the wake’s–it can generate disturbances that are problematic in flight. Being able to predict and avoid such behavior is important for safe aircraft. (Photo credit: S. Makiya et al.)
Water Entry
In the image above we see two spheres of the same size, shape, and material being dropped into water. The left sphere has almost no splash, whereas the one on the right has a spectacular curtain-like splash. Why the big difference? It all comes down to the surface treatments. The glass sphere on the left is hydrophilic, but the right one has been treated to be hydrophobic. As a result, the water-fearing molecules of that sphere push the water away, allowing air to be entrained below the water’s surface instead. This creates a big splash that’s absent when the water moves smoothly around the hydrophilic sphere. (Photo credit: L. Bocquet et al.)
