FYFD

Tag: flow visualization

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    Dancing Over Ridges

    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.)

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    Turbulence From Vortex Rings

    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.)

  • The Best of FYFD 2022

    The Best of FYFD 2022

    In keeping with our annual tradition, here’s a look back at the most popular posts of 2022:

    1. The Assassin’s Teapot can pour two different liquids from the same spout
    2. The Florida Keys formed from fossilized coral reefs and sandbars
    3. Take a look inside a gas pump’s nozzle
    4. Hot chocolate hides a strange acoustic effect
    5. Under strong electric fields, liquid bridges form
    6. Growing fractal fluids
    7. A peek inside a coronavirus aerosol
    8. Wind-powered Strandbeests wander the beaches
    9. Tongan volcano sends shocks around the world
    10. Why do tea leaves swirl up in the middle of a stirred mug?

    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)

  • To Fizz or Not to Fizz

    To Fizz or Not to Fizz

    Place a drop of carbonated water on a superhydrophobic surface and it will slide almost frictionlessly, much the way Leidenfrost drops do. The drop behaves this way thanks to the self-produced layer of carbon dioxide vapor that it levitates on. As the gas escapes, the drop eventually settles back into contact with its surface. But until then, its levitation makes for some fun.

    On the treated half of the glass (left), bubbles form a continuous film against the glass. On the untreated side (right), bubbles nucleate, grow, and rise as expected for a fizzy drink.
    On the treated half of the glass (left), bubbles form a continuous film against the glass. On the untreated side (right), bubbles nucleate, grow, and rise as expected for a fizzy drink.

    Single droplets aren’t the only source of fun, however. In the images above, researchers coated the left half of a wine glass with a superhydrophobic treatment, while leaving the right half of the glass untouched. Once (dyed) carbonated water is poured into the glass, we see a bizarre dichotomy. In the right, untreated half of the glass, carbon dioxide bubbles nucleate, grow, and rise through the glass. But on the left side, the liquid appears still and bubble-less. In fact, the carbon dioxide gas on the left side is forming a continuous bubble film by the surface of the glass! (Image, video, and research credit: P. Bourrianne et al., see also)

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    Snowing in the Core

    Some rocky planetary bodies, like Jupiter‘s moon Ganymede, generate magnetic fields through snow-like, solid precipitation that falls in their liquid metal cores. To study this peculiar and complex arrangement, researchers look at sugar grains falling through — and dissolving into — water. The solid sugar grains mimic the iron snowflakes that fall in Ganymede’s core. As they sink, they drag fluid with them. But the grains can also dissolve, making the fluid around them denser and prone to sinking even faster. The dense, sinking flows trigger buoyant convection inside the surrounding fluid.

    As seen in the experiments, there are many factors competing here. Large grains dissolve more slowly and are able to drag more fluid with them as they fall. Small grains, on the other hand, dissolve quickly, causing more buoyancy-driven flows. Laboratory analogs like these help scientists unravel the complexities of situations we cannot observe otherwise. (Image and video credit: Q. Kriaa et al.)

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    Self-Propelled Droplets

    Drops of ethanol on a heated surface contract and self-propel as they evaporate. My first thought upon seeing this was of Leidenfrost drops, but the surface is not nearly hot enough for that effect. Instead, it’s significantly below ethanol’s boiling point. Looking at the drops in infrared reveals beautiful, shifting patterns of convection cells on the drop. The patterns are driven by the temperature difference along the drop; at the bottom, the drop is warmest, and at its apex, it is coldest. Those differences in temperature create differences in surface tension, which drives a surface flow that breaks the drop’s symmetry. The asymmetry, the authors suggest, is responsible for the drop’s propulsion. (Image and video credit: N. Kim et al.)

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    “A Sense of Scale – Reminiscence”

    In so much of fluid dynamics, size does not matter. We see the same patterns mirrored across nature from a fuel injection nozzle to galactic clusters. And no one plays with that sense of scale better than artist Roman De Giuli, whose microscale practical effects give the impression of flying above glittering alien coastlines. Ink and paint squeeze around craggy islands, leaving perfect streamlines to mark their passage. Fractal fingers expand like river deltas seeking the path to the sea. Enjoy more of De Giuli’s work on his website and Instagram. (Image and video credit: R. De Giuli; via Colossal)

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    Draining a Bottle

    Turn a bottle upside-down to empty it, and you’ll hear a loud glug-glug-glug as the liquid in the bottle empties and air rushes in. In this video, researchers aim a high-speed camera at the very first bubble that forms during the process. Once the bubble reaches the wider area of the bottle, it tends to pinch off in the bottle’s neck. That creates a narrow jet that pierces the bubble and flies all the way to the other side, leaving a column of liquid inside the rising bubble. Increasing the fluid’s viscosity has remarkably little effect, at least until the liquid is extremely viscous. (Image and video credit: H. Mayer et al.)

  • Waves in Liquid Crystals

    Waves in Liquid Crystals

    Liquid crystals are now ubiquitous in displays, but scientists are still discovering new properties for this state of matter. Here, a team explores nematic liquid crystals, whose rod-like shape rotates in three dimensions as they apply a voltage. The layer of liquid crystals is held between polarizing filters, creating regions of light and dark that depend on the liquid crystals’ orientations.

    Traveling waves and other wave patterns form in this liquid crystal as the voltage applied to it increases.
    Traveling waves and other wave patterns form in this liquid crystal as the voltage applied to it increases.

    As the researchers increase the voltage, traveling waves form. With higher voltages, the waves appear to slow a stop. The slowing waves result from the molecules tilting far from a vertical orientation, which makes it harder for individual molecules to rotate since they experience greater resistance from their neighbors. (Image, video, and research credit: V. Panov et al.; via APS Physics)

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    Classifying Waves

    In a lab, researchers create their waves in a long, clear-sided tank, where they can observe how the waves form, travel, and interact. To generate the wave, they use a plate, attached to a piston. Push the water at one end, and a wave forms. The type of wave that forms depends on both the velocity and the stroke length of the piston, as shown in this video. By mapping out these two variables, researchers can observe all different sorts of waves, from peaceful solitary waves to wild, plunging breakers. (Image and video credit: W. Sarlin et al.)