Year: 2016

Fluids Round-up
Time for another look at some of the best fluids content out there. It’s the fluids round-up – with a special focus this week on oceans!
– Ryan Pernofski spent two years filming the ocean in slow motion with his iPhone to make the short film “Slowmocean” seen above. It’s a gorgeous ode to the beauty of breaking waves.
– Oceans with higher salinity than Earth’s could drive global circulation that would make exoplanets more hospitable to life.
– Speaking of alien oceans that could harbor signs of life, there’s discussion afoot of how future missions to icy moons like Europa or Enceladus could collect samples from plumes ejected from beneath the ice.
– Wind and waves make harsh, erosive environments. This photo essay from SFGate shows how greatly the sands of Pacifica shift over time. (submitted by Richard)
Bonuses:
– New research explores how Martian mountains may have been carved out by the wind.
– Ever listened to an orchestra made from ice? You should! Learn about Tim Linhart, who builds and maintains ice instruments. (submitted by ashketchumm)
– MIT has demonstrated a new 3D-printing technique that allows for printing liquid and solid parts simultaneously, allowing would-be creators to rapid-prototype hydraulically-driven robotics.
Even more bonus bonus!
– ICYMI, the new FYFD video made Gizmodo!
If you’re a fan of FYFD, please consider becoming a patron. As a bonus, you’ll get access to this weekend’s planetary science webcast!
(Video credit: R. Pernofski; via Flow Visualization; Pluto image credit: NASA/APL)
April 14, 2016
The Brazil Nut Effect
The Brazil nut effect is a common name for the phenomenon where large particles tend to rise to the top of a mixture when it’s shaken. It’s also the subject of the latest FYFD video, which you can see above.
I’ve seen other mentions of the topic previously, but when I started researching the literature, I discovered that the Brazil nut effect was much more complicated than I’d thought! Hopefully, you’ll find the results as interesting as I did. And if you want to dig further, there are links to the papers I used over on YouTube.
Filming was also interesting this time around. I tried out stop-motion animation for the first time. It takes so much patience! But I think the results are so cute. (Image and video credit: N. Sharp/FYFD)
April 13, 2016
Upcoming Webcast
This weekend I’ll be holding my second live webcast for FYFD patrons. This month we’ll be focusing on the subject of planetary science, one of the coolest applications out there for fluid dynamics. My guests will be Keri Bean, a NASA JPL mission operations engineer and atmospheric scientist, and Professor Geoffrey Collins, a geologist at Wheaton College in Massachusetts. Keri has worked on all the recent Martian missions, including Mars Curiosity and the Phoenix Lander. She currently works on operations for the Dawn mission to Ceres. Geoff studies the geophysics of icy planets and moons like Pluto and Titan. He was part of the Galileo and Cassini missions to Jupiter and Saturn and is currently part of the team working on a future mission to Europa.
April 12, 2016
A Rocket Launch From Above
Rocket launches often produce spectacular imagery, but it’s rare to get a launch view quite like this one. The photograph above shows the recent launch of an Atlas V rocket as viewed from the International Space Station. The rocket itself is too small to be seen directly. Instead, that bright spot you see is the rocket’s exhaust. The smoky swooping curves mark the rocket’s exhaust plume. Because the gases leaving the rocket are at much higher pressure than the scant air pressure in the upper parts of the atmosphere, the exhaust expands rapidly, ballooning outward. Here the water vapor in the exhaust has frozen into crystals that catch the sunlight and make them stand out against the surrounding sky. (Image credit: NASA; via NASA Earth Observatory)
April 12, 2016
Plasma Flow Control
Engineers frequently face the challenge of maintaining control of air flow around an object across a wide range of conditions. After all, wind turbines and airplanes don’t always get to choose the perfect weather. To widen their operating ranges, designers can use active flow control to keep air flowing around an airfoil instead of separating and causing stall. One method of flow control uses plasma actuators on the upper surface of an airfoil. When activated, the plasma actuator ionizes air near the wing surface, producing the purplish glow seen above. That ionized air, or plasma, gets accelerated by the electric field of the device. The acceleration adds momentum to air near the wing surface, which helps it stay attached and flowing smoothly despite the unfavorable pressure conditions near the trailing edge of the wing. Compared to other methods of active flow control, plasma actuation is relatively simple to implement and so is actively being researched for applications in aviation and wind energy. (Image and research credit: I. Brownstein et al., source)
April 11, 2016
Bonbon Coatings
If you’ve ever bitten into a chocolate-covered bonbon, you may have noticed that the candy’s chocolate coating is remarkably uniform. Inspired by this observation, a group of engineers have investigated how viscous fluids poured over a curved surface flow and solidify; their findings were published this week.
Rather than heated chocolate, the group used polymer-filled fluids that cure and harden over time. Interestingly, they found that the final shell is quite uniform and that its thickness does not depend on the pouring technique. Instead, they can predict the final shell thickness based on the radius of the mold and the rheological properties of the fluid–specifically its density, viscosity, and curing time. The reason for this is that the time it takes for the fluid to drain and coat the mold is much shorter than the time it takes for the polymer to cure. As a result, the amount of fluid that sticks to the mold depends on geometry and fluid properties – not how the fluid was poured.
Amateur confectioners rejoice: pouring uniform chocolate coatings may be easier than you thought! (Image credit: MIT News, video; research credit: A. Lee et al.)
April 8, 2016
Underwater Explosions
Underwater explosions are incredibly dangerous and destructive, and this animation shows you why. What you see here are three balloons, each half-filled with water and half with air. A small explosive has been set off next to them in a pool. In air, the immense energy of an explosion actually doesn’t propagate all that far because much of it gets expended in compressing the air. Water, on the other hand, is incompressible, so that explosive energy just keeps propagating. For squishy, partially air-filled things like us humans or these balloons, that explosion’s force transmits into us with nearly its full effect, causing expansion and contraction of anything compressible inside us as our interior and exterior pressures try to equalize. The results can be devastating. To see the equivalent experiment in air, check out Mark Rober’s full video on how to survive a grenade blast. (Image credit: M. Rober, source)
April 7, 2016
Going With The Flow
Going with the flow
Guys, I’m in Science! WHHHAAAAT?
April 6, 2016
Fluttering Feathers
Birds do not always vocalize in order to make their songs. The male African broadbill, shown in the top video above, makes a very distinctive brreeeet in its flight displays, but as newly published research shows, the sound comes from its wings, not its voice. During the display, the broadbill spreads its primary feathers and sound is produced on the downstroke, when wingtip speeds reach about 16 m/s. By filming a broadbill wing with a high-speed camera in a wind tunnel at comparable air speeds, researchers could localize the sound production to the 6th and 7th primary feathers.
In the second video above, you can see these feathers twisting and fluttering in the breeze. This is an example of aeroelastic flutter, a phenomenon in which aerodynamic and structural forces couple to induce oscillations. The same phenomenon famously caused the collapse of the Tacoma Narrows Bridge in 1940. In the birds, however, the flutter is non-destructive and the vibration produces audible sound which the other feathers modulate into the calls we hear. Broadbills aren’t the only birds to use this trick; some species of hummingbirds use flutter in their tail feathers during mating displays. (Video, image, and research credits: C. Clark et al.; additional videos here)
April 6, 2016
Bumblebees in Turbulence
Bumblebees are small all-weather foragers, capable of flying despite tough conditions. Given the trouble that micro air vehicles have when flying in gusty winds, bumblebees can help engineers to understand how nature successfully deals with turbulence. Under smooth laminar conditions like those shown in the animation above, bumblebees stay aloft by beating their wings forward and backward in a figure-8-like motion. On both the forward downstroke and the backward upstroke, you’ll notice a blue bulge near the front of the bee’s wing. This is a leading-edge vortex, which provides much of the bee’s lift.
Researchers were curious how adding turbulence would affect their virtual bee’s flight. The still image above shows the bee in moderate freestream turbulence (shown in cyan). Surprisingly, this outside turbulence has very little effect on the flow generated by the bee, shown in pink. In fact, the researchers found that the bees could fly through turbulence without a significant increase in power. Too much turbulence does make it hard for the bee to control its flight, though. The bee’s shape makes it prone to rolling, and the researchers estimated, based on a bee’s 20 ms reaction time, that bumblebees can probably only correct that roll and maintain controlled flight at turbulence intensities less than 63% of the mean wind speed. (Image credits: T. Engels et al., source; via Physics Focus)
April 5, 2016