It’s tough to get much closer to flowing lava than this video of freshly forming coastline in Hawaii. Lava is complex fluid, with viscous properties that vary significantly with chemical composition, temperature and deformation. Here, despite being very viscous, the lava flows quickly–perhaps even turbulently. Several times it forms a heap and even shows signs of the rope-coiling instability familiar from viscous fluids like honey. All in all, it’s quite mesmerizing. (Video credit: K. Singson; submitted by Stuart B.)
Tag: fluid dynamics
How Rain Gets Its Smell
Light rain after a dry spell often produces a distinctive earthy scent called petrichor that is associated with plant oils and bacteria products. How these chemicals get into the air has been unclear, but new research suggests that the mechanism may come from the rain itself. When water falls on a porous surface like soil, tiny air bubbles get trapped beneath the drop. These bubbles rise rapidly due to buoyancy and, upon reaching the surface, burst and release tiny droplets known as aerosols. Depending on the surface properties and the drop’s impact speed, a single drop can produce a cloud of aerosol droplets. The research team is now investigating how readily bacteria or pathogens in the soil can spread through this mechanism. Other human-focused research has already shown that these tiny aerosol droplets can persist in the air for remarkably long periods and may help spread diseases. (Video credit: Massachusetts Institute of Technology; research credit: Y. Joung and C. Buie; submitted by Daniel B and entropy-perturbation)
Swimming Through Sand
Shovel-nosed snakes and sandfish lizards both swim through granular materials like sand. Researchers at Georgia Tech used x-rays to observe their subsurface motions. Despite their different shapes, the long, slender snake and the shorter, wider lizard both move under the sand by projecting traveling waves along their bodies. The snake’s long, skinny body allows it to have more bends along its length, which increases its transport efficiency because it allows the snake to move mostly through the tunnel created by its head’s passage. In contrast, the sandfish’s motions fluidize the sand around it, enabling it to swim. Although the snake is faster, both animals have optimized their motions for fast, low-energy transit according to their body type. (Video credit: Georgia Tech; research credit: S. Sharpe et al.; via io9)
“Heavy Metals”
Photographer Alberto Seveso’s “Heavy Metals” series builds on his previous works capturing fluid dynamics. By dropping mixtures of ink, liquids, and metallic powder through different fluids, he creates ethereal, billowing forms that turn the processes of diffusion and turbulent mixing into something one could almost touch. Be sure to check out the rest of the series and his online portfolio for more examples. (Photo credits: A. Seveso; via Colossal; submitted by jshoer and @catnogood)
Fire-Breathing
In this high-speed video, the Slow Mo Guys demonstrate fire-breathing. Rather than using a liquid fuel like kerosene, they utilize cornstarch, which is both easily flammable and non-volatile thanks to its powdered form. Blowing out the cornstarch creates a turbulent jet of cornstarch and air. Combine that with a combustion source, and the cornstarch quickly deflagrates, meaning that the flame propagates via heat transfer. When neighboring regions of cornstarch become hot enough, they ignite and the flame front expands. You can observe this in the flame growth shown in the video; just after ignition the cornstarch jet is much wider than the fire and it takes some time for the flames to catch up with the jet. Although a liquid-fueled fireball operates by the same principles, it can look rather different. For comparison, check out this high-speed video of a WD-40 fireball. And, hopefully it goes without saying, but don’t try this stuff at home. (Video credit: The Slow Mo Guys)
Hand Dryers and Atomization
Some newer electric hand dryers, like the Dyson Airblade, use jets of high-speed air to dry hands faster than traditional models. Much of their effectiveness comes from the rapid atomization–or break-up into tiny droplets–of water on one’s hands. This is demonstrated in the animation above, which comes from a high-speed video of a water drop falling through the jets of a homemade dryer. Breaking up the water quickly disperses the microdroplets but it also speeds up evaporation by greatly increasing the exposed surface area of the water. This is similar to how you can get instant snow from throwing boiling water if it’s cold enough outside. (Image credit: tesla500, source video; submitted by Nick)
Interrupting Sediments
The pier at Progreso extends 6.5 kilometers into the Gulf of Mexico, creating an artificial obstruction to ocean flow and sediment transport near the shore. The first 2 kilometers of the pier are built on arches that allow some flow through, but the newer sections do not. Prevailing winds act from the east-northeast, driving flow roughly right to left in the image. The sediment traces flow around the pier and reveals the complicated flow-shadow downstream of the newer parts of the pier. (Image credit: NASA Earth Observatory)
Skydiving in Wind Tunnels
Skydivers and freefall acrobats utilize vertical wind tunnels as ground training facilities. Low-speed acrobatics, like gymnastics, relies on inertial forces and angular momentum for flips and attitude changes. But at freefall speeds, aerodynamic forces are much larger, and an acrobat’s orientation relative to the flow has a big effect on his stability and maneuverability. Simple movements of an arm or leg can significantly alter one’s aerodynamics, allowing the acrobats to choreograph controlled and synchronized motion. (Video credit: Red Bull)
Author’s note – After much consideration, I’ve decided to move FYFD to a MWF posting schedule for the time being. Working full-time has its limitations, and I believe the less frequent posting schedule will allow me to dedicate more time to generating new content like FYFD videos. This was a tough decision, but I hope it will help FYFD grow in the long-term. – Nicole
Lava-Driven Waterspouts
Seven waterspouts align as lava from the Hawaiian volcano Kilauea pours into the ocean in this striking photo from photographer Bruce Omori. Like many waterspouts–and their landbound cousins dust devils–these vortices are driven by variations in temperature and moisture content. Near the ocean surface, air and water vapor heated by the lava create a warm, moist layer beneath cooler, dry air. As the warm air rises, other air is drawn in by the low pressure left behind. Any residual vorticity in the incoming air gets magnified by conservation of angular momentum, like a spinning ice skater pulling her arms in. This creates the vortices, which are made visible by entrained steam and/or moisture condensing from the rising air. (Photo credit: B. Omori, via HPOTD; submitted by jshoer)
Top 10 FYFD Posts of 2014
It’s only fitting to take a moment to look back at 2014 as we step into the New Year. It was a big year in many respects – we hit 1000 posts and broke 200,000 followers; I started producing FYFD videos on our YouTube channel; and, on a personal note, I finished up my PhD. But since we’re all about the science around here, I will give you, without further ado, the top 10 FYFD posts of 2014:
1. Bioluminescent crustaceans use light for defense
2. What happens when you step on lava
3. Flapping flight deconstructed
4. Wingtip vortices demonstrated
5. Saturn’s auroras
6. Raindrops’ impact on sand
7. Water spheres in microgravity
8. The surreal undulatus asperatus cloud
9. Inside a plunging breaker
10. A simply DIY Marangoni effect demoI can’t help but notice that 9 out of the 10 posts feature animated GIFs. Oh, Tumblr, you rascals. Happy New Year! (Image credits: BBC; A. Rivest; E. Lutz; Nat. Geo/BBC2; ESA/Hubble; R. Zhao et al.; D. Petit; A. Schueth; B. Kueny and J. Florence; Flow Visualization at UC Boulder)
