Bubbly Tornadoes Aspin

Rotating flows are full of delightful surprises. Here, the folks at the UCLA SpinLab demonstrate the power a little buoyancy has to liven up a flow. Their backdrop is a spinning tank of water; it’s been spinning long enough that it’s in what’s known as solid body rotation, meaning that the water in the tank moves as if it’s one big spinning object. To demonstrate this, they drop some plastic tracers into the water. These just drop to the floor of the tank without fluttering, showing that there’s no swirling going on in the tank. Then they add Alka-Seltzer tablets.

As the tablets dissolve, they release a stream of bubbles, which, thank to buoyancy, rise. As the bubbles rise, they drag the surrounding water with them. That motion, in turn, pulls water in from the surroundings to replace what’s moving upward. That incoming water has trace amounts of vorticity (largely due to the influence of friction near the tank’s bottom). As that vorticity moves inward, it speeds up to conserve angular momentum. This is, as the video notes, the same as a figure skater’s spin speeding up when she pulls in her arms. The result: a beautiful, spiraling bubble-filled vortex. (Video and image credit: UCLA SpinLab)

#buoyancy #conservationOfAngularMomentum #flowVisualization #fluidDynamics #physics #rotatingFlow #science

The Best of FYFD 2024

Welcome to another year and another look back at FYFD’s most popular posts. (You can find previous editions, too, for 2023, 2022, 2021, 2020, 2019, 2018, 2017, 2016, 2015, and 2014. Whew, that’s a lot!) Here are some of 2024’s most popular topics:

• The Taum Sauk Dam Failure and Its Legacy
• Stretching Ant Rafts
• Gigapixel Supernova
• Feynman’s Sprinkler Solved
• Calming the Waves
• “Dew Point” Deposits Droplets
• Drying Unaffected by Humidity
• Trapped in a Taylor Column
• Exciting a Flame in a Trough
• Remembering Rivers Past
• A Comet’s Tail
• Light Pillars
• Liquid Metal Printing
• The Miscible Faraday Instability
• A Triangular Prominence

This year’s topics are a good mix: fundamental research, civil engineering applications, geophysics, astrophysics, art, and one good old-fashioned brain teaser. Interested in what 2025 will hold? There are lots of ways to follow along so that you don’t miss a post.

And 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, 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: dam – Practical Engineering, ants – C. Chen et al., supernova – NOIRLab, sprinkler – K. Wang et al., wave tank – L-P. Euvé et al., “Dew Point” – L. Clark, paint – M. Huisman et al., iceberg – D. Fox, flame trough – S. Mould, sign – B. Willen, comet – S. Li, light pillars – N. Liao, chair – MIT News, Faraday instability – G. Louis et al., prominence – A. Vanoni)

#admin #ants #astrophysics #civilEngineering #comet #damFailure #drying #flowVisualization #fluidDynamics #fluidsAsArt #FYFD #instability #physics #plasma #rivers #rotatingFlow #science #selfExcitedOscillation #TaylorColumn #waveInterference

How Magnetic Fields Shape Core Flows

The Earth’s inner core is a hot, solid iron-rich alloy surrounded by a cooler, liquid outer core. The convection and rotation in this outer core creates our magnetic fields, but those magnetic fields can, in turn, affect the liquid metal flowing inside the Earth. Most of our models for these planetary flows are simplified — dropping this feedback where the flow-induced magnetic field affects the flow.

The simplification used, the Taylor-Proudman theorem, assumes that in a rotating flow, the flow won’t cross certain boundaries. (To see this in action, check out this Taylor column video.) The trouble is, our measurements of the Earth’s actual interior flows don’t obey the theorem. Instead, they show flows crossing that imaginary boundary.

To explore this problem, researchers built a “Little Earth Experiment” that placed a rotating tank (representing the Earth’s inner and outer core) filled with a transparent, magnetically-active fluid inside a giant magnetic. This setup allowed researchers to demonstrate that, in planetary-like flows, the magnetic field can create flow across the Taylor-Proudman boundary. (Image credit: C. Finley et al.; research credit: A. Pothérat et al.; via APS Physics)

#fluidDynamics #magnetohydrodynamics #physics #planetaryScience #rotatingFlow #science #TaylorColumn #TaylorProudmanTheorem

The world’s largest iceberg, A23a, is stuck. It’s not beached; there are a thousand meters or more of water beneath it. But thanks to a quirk of the Earth’s rotation, combined with underwater topology, A23a is stuck in place, spinning slowly for the foreseeable future. A23a is trapped in what’s known as a Taylor column, a rotating column of fluid that forms above submerged objects in a rotating flow. You can see the same dynamics in a simple tabletop tank.

When a tank (or planet) is rotating steadily, there’s little variation in flow with depth. With an obstacle at the deepest layer — in this case, an underwater rise known as the Pirie Bank — water cannot pass through that lowest layer. And that deflection extends to all the layers above. The water above Pirie Bank just stays there, as if the entire column is an independent object. Caught inside this region, A23a will remain imprisoned there. How long will that last? There’s no way to know for sure, but a scientific buoy in another nearby Taylor column has been hanging out there for 4 years and counting. (Image credit: A23a – D. Fox/BAS, diagram – IBSCO/NASA; via BBC News; submitted by Anne R.)

https://fyfluiddynamics.com/2024/08/trapped-in-a-taylor-column/

#fluidDynamics #geophysics #oceanography #physics #rotatingFlow #science #TaylorColumn