In his recent short film, artist Roman De Giuli explores turbulence using metallic paints and inks in a fishtank. The effects are beautiful: sparkling pigments dispersing in clouds, mushroom- and umbrella-shaped Rayleigh-Taylor instabilities, and lots of swirling eddies. It’s exactly the kind of eyecandy to kick off your weekend with! (Image and video credit: R. De Giuli)
One way to explore the effects of spinning liquids at high-speeds is to build an expensive and precise lab apparatus. Another method is to raid the Lego bin. Here, a YouTuber builds ever-more-elaborate Lego constructions to spin a sphere of water. He begins with a relatively straightforward magnetic stirrer that creates a bathtub vortex in his sphere, but as the set-up grows, he eventually encases the sphere to spin the entire thing at high-speed. It’s a cool way to see how spinning liquids react, from forming a vortex to spin coating the interior of the sphere and to generating a parabolic interface between air and liquid. Set-ups like these are not merely for fun, though; scientists use them to simulate the interiors of planets. (Image and video credit: Brick Technology; submitted by clogwog)
Soft colors and sudden coalescence combine in this short film from Susi Sie’s team. The visuals rely on liquid lenses (likely oil) floating atop a water bath. You can see how the fluids get manipulated in their behind-the-scenes video, which also provides a peek at how the sound effects get made. (Video credit: S. Sie et al.)
Toilet flushes are gross. We’ve seen it before, though not in the same detail as this study. Here, researchers illuminate the spray from the flush of a typical commercial toilet, like those found in many public restrooms. They found that flushing generates a plume of droplets that reaches 1.5 meters in under 8 seconds, producing many thousands of droplets across a range of sizes.
The experiments were conducted in a ventilated lab space, and the flushes involved only clean water — no fecal matter or toilet paper — so they don’t perfectly mimic the confines of a public toilet stall. But the implications are still pretty gross. Without a lid to contain the flush’s spray, these energetic toilets are spraying droplets capable of carrying COVID, influenza, and other nastiness all over our bathrooms. (Image and research credit: J. Crimaldi et al.; via Gizmodo)
Gravity currents carry denser fluids into lighter ones, like cold air drifting under your door in winter or dense fogs flowing downhill in San Francisco. Here, researchers visualize the situation using denser salt water flowing into fresh water. Once the gate separating the two fluids rises, the salt water slides down an artificial slope into the fresh water.
Very quickly the flow forms a Kelvin-Helmholtz instability due to the different flow speeds between the two fluids. Kelvin-Helmholtz waves form distinctive swirls and billows that are reminiscent of a cat’s eye. As the swirls rotate, they can flow over one another, and break up into turbulence. (Image and video credit: C. Troy and J. Koseff)
In nature, icicles often form horizontal ripples along their outer surface. Researchers found that these shapes only form when impurities are present in the water forming icicles; icicles made from pure water are smooth. Now researchers are uncovering more details of the ripple formation process, though the underlying mechanism remains unknown.
Researchers first grew wavy icicles, then melted through them to reveal cross-sections of the icicle. They found chevron-like patterns within the ice, corresponding to areas with higher concentrations of impurities. The team think these chevrons record the process by which flowing water accumulates on the surface of the icicle prior to freezing. (Image credit: top – M. Shturma, cross-sections – J. Ladan and S. Morris; research credit: J. Ladan and S. Morris; via APS Physics)
Capturing what goes on inside a combustion engine is incredibly difficult. It’s a problem that depends on turbulent flow, chemistry, heat transfer, and more. To represent all of those aspects in a numerical simulation requires enormous computational resources. It’s not simply the realm of a supercomputer; it requires some of the fastest supercomputers in existence.
Exascale computing, like that used for the simulations in this video, is defined as at least 10^18 (floating-point) operations per second. For comparison, my PC has a recent, high-end graphics card, and it’s about a million times slower than that. These are absolutely gigantic simulations. (Image and video credit: N. Wimer et al.)
When flowing over a ridged surface, particles follow a drifting, helical trajectory. In this video, researchers delve into the physics behind this phenomenon. Differences in the pressure gradient along different parts of the corrugation push particles along the groove. With their analysis, the team is able to predict particle trajectories above surface roughness of any shape. With these tools, they can design roughened microchannels that disperse particles at a desired speed, something that could be especially helpful in medical diagnostics. (Image and video credit: D. Chase et al.; research credit: D. Chase et al.)
When vortex rings collide, they reconnect into smaller, rings that eventually break down into chaos. Here, researchers experiment with colliding multiple vortex rings — focusing on an eight-ring collision. When they collide rings over and over, it creates a zone of isolated turbulence at the heart of the collisions.
Many of the theories and predictions that exist around turbulence assume that the flow is homogeneous and isotropic; what this means is that the (statistical) characteristics of the flow are the same in every direction. In reality, this kind of flow isn’t always easily achieved, which makes testing theoretical predictions challenging.
What’s neat about this set-up is that you get this desired turbulence in a very controlled way. It’s easy to tune the size and energy of your vortex rings, and those tweaks allow you to observe what — if any — changes occur in the resulting turbulence. (Image and video credit: T. Matsuzawa et al.)
In keeping with our annual tradition, here’s a look back at the most popular posts of 2022:
Lots of beverage-inspired posts this time around! It’s a good reminder that there’s always interesting science around us all the time. Also, a special shout out to Steve Mould, whose videos appear in three of the top ten posts of the year – wow! Congrats, Steve!
If you enjoy FYFD, please remember that it’s a reader-supported website. I don’t run ads and it’s been years since my last sponsored post. You can help support the site by becoming a patron, making a one-time donation, buying some merch, or simply by sharing on social media. And if you find yourself struggling to remember to check the website, remember you can get FYFD in your inbox every two weeks with our newsletter. Happy New Year!
(Image credits: teapot – S. Mould, Florida Keys – L. Dauphin/USGS, gas pump – S. Mould, hot chocolate – C. Kalelkar, liquid bridge – X. Pan et al., fractal fluids – R. Camassa et al., coronavirus – R. Amaro et al., strandbeests – T. Jansen, shocks – S. Doran/Himawari 8, tea leaves – S. Mould)