FYFD

Tag: fluid dynamics

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    Levitating By Squeeze Film

    We’ve seen a few different kinds of levitation here over the years, including via acoustic waves, aerodynamics, and Leidenfrost effect. Here, Steve Mould describes something a bit different: a levitation squeeze film driven by ultrasonic transducers. Like a vibrating droplet, the thing keeping surfaces apart here is a thin, lubricating layer of air. The vibration of the ultrasonic transducer squeezes and replenishes the air layer quickly enough that it can keep transducers aloft. Steve even manages to create a miniature airless “air hockey” table with it! (Video and image credit: S. Mould)

  • Dragonfly Dogfights

    Dragonfly Dogfights

    Like fighter pilots of old, male dragonflies engage in aerial combat where each tries to outmaneuver the other to keep a sight on their rival’s tail. A recent study observed this combat in the field and uncovered some surprising similarities to dogfighting. Like pilots, dragonflies used spiraling turns and other high-g moves to gain an advantageous position behind the other. In human combat, that position favors the forward-facing weapons of the pilot in back; for dragonflies, it keeps their rival in the part of their vision that best detects movement.

    Interestingly, the team found that–even in the midst of combat–dragonflies spent at least a third of their time gliding. It’s unclear whether they glide to conserve energy or because it’s easier to track a rival when gliding.

    The authors dig into the control rules needed for dragonflies to execute these chases and found that even relatively simple control schemes–constrained by the dragonfly’s physical limits–result in complex flight contests. (Image and research credit: S. Fabian et al.; via Ars Technica)

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    Blowing Droplets Apart

    In raindrops, ink-jet printing, and spray painting, droplets get broken apart by the air flowing around them. Here, researchers investigate how a jet of fluid can push a droplet from its perch, or–with enough momentum–shatter the droplet. There are some lovely flow visualizations here; it’s especially cool to see the starting vortex ring of the jet push and deform the droplet. (Video and image credit: S. Jain et al.)

  • Salt and Dunes

    Salt and Dunes

    Photographer Barbara Brown captured these striking aerial views in Namibia. Coastal dunes and saltworks feature in the photos from Walvis Bay, where wind, waves, evaporation, and humankind have shaped the landscape. The colorful and dendritic dune images come from Sossusvlei, where the ephemeral Tsauchab River ends in the Namib Desert. Recent flooding left its mark on the dry landscape. (Image credit: B. Brown/IAPOTY; via Colossal)

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  • How Corals Stir

    How Corals Stir

    Reef-building coral polyps constantly stir the water around them with dense carpets of microscopic hair-like cilia. The beating of the cilia helps polyps feed while also pushing away sediment and debris. Their stirring increases nutrient and gas exchange with seawater, too. A new study combines experimental measurements with a simple mathematical model to recreate the three-dimensional flows corals make. The model’s efficiency means it should be useful for future studies of how corals and other cilia-covered systems interact with bacteria or other active particles. (Image and research credit: S. Selvan et al.; via APS)

    Particle tracks showing stirring created by coral cilia.
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    The Subtleties of Pipe Flow

    If you put a thumb over your hose’s outlet, you get a faster jet, but how does that affect the flow rate? That’s the question Grady starts from in this Practical Engineering video exploring pipe flow physics. From continuity and control volumes to practical losses, he touches on both the theory and practice behind this all-important aspect of engineering. Pipe flow is often where engineering students begin their studies of fluids, but that doesn’t mean it’s easy! (Video and image credit: Practical Engineering)

  • Screening for Sleep Apnea

    Screening for Sleep Apnea

    Snoring and sleep apnea–a condition where aeroelastic flutter obstructs the airway and stops breathing during sleep–often go hand-in-hand. But diagnosing sleep apnea involves an expensive and time-consuming screening in which the patient has to sleep while monitored by various sensors. To make the process easier, researchers are developing a screening method based only on audio recording.

    They started with a pre-trained audio model designed for speech recognition and stripped back computationally-expensive layers that weren’t relevant to snoring. Then they trained the new model using labeled audio data taken from standard clinical testing for sleep apnea. That means the model was told which audio recordings corresponded to “normal” snoring and which showed signs of sleep apnea. From there, the model was able to correctly identify apnea-related audio from fresh recordings just under 74% of the time. While that accuracy isn’t high enough to use the tool for diagnosis, it could help patients pre-screen for sleep apnea at home to decide whether the more invasive testing is warranted. (Image credit: L. Cline; research credit: H. Li et al.; via Physics World)

  • Microplastics in the Water Column

    Microplastics in the Water Column

    Of the more than 9 billion metric tons of plastic that’s been produced, a mere 9% has been recycled. About 12% has been incinerated, and the remainder is just out there–in our homes, our landfills, and, unfortunately, in our oceans. Exactly where all the plastic is continues to be an active question of research.

    Plastic’s density is similar to that of water; some versions are a little denser than water, and some are a little lighter. So whether a piece of plastic floats at the ocean surface or sinks to the bottom depends on several factors, including its density, size, and shape. A large, dense plastic–think laundry detergent bottles–can float if it displaces enough water; after all, metal ships float!

    But as sunlight and abrasion breaks that big container into smaller fragments, their buoyancy shrinks. Eventually, these small, millimetric pieces sink, carrying our pollution to ecosystems we once thought remote. Some of the highest rates of microplastic ingestion are found in nonmigratory species living between 1200 and 1500 meters below the surface. We may never visit those depths, but our garbage does. (Image credit: iStock/dottedhippo; via Eos)

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  • “Supercell”

    “Supercell”

    A supercell thunderstorm in New Mexico appears almost otherworldly in this photo from Dennis Hualong Zhang. Glowing from within and stacked like a layer cake, the storm menaces the nearby road and fields. Lightning in the distances completes the composition. Images like this are a reminder that our atmosphere–despite frequently seeming calm and ordinary–harbors incredible turbulent energy. (Image credit: D. Zhang; via ILPOTY)

    "Supercell" by Dennis Hualong Zhang.
  • Ice Giant or Magma Ocean World?

    Ice Giant or Magma Ocean World?

    Uranus and Neptune–known as our system’s ice giants–are our least explored planets. Both have received exactly one flyby, from the Voyager 2 spacecraft. The data from those flybys remain our primary source of knowledge about each planet. The traditional model for each planet’s interior (dating back to before the flybys) consists of three layers: a rocky core; an icy mantle made up of water, ammonia, and methane; and a hydrogen/helium-rich atmosphere. That structure is one way to match the limited measurements we have from these planets, but, as today’s preprint study points out, it’s not the only way.

    The authors suggest an alternative structure, in which a hydrogen-rich atmosphere overlays a supercritical magma ocean capable of dissolving hydrogen into heavier, metallic elements. Their suggestion is motivated by several factors. First, objects in the outer solar system–including Kuiper Belt objects–have less icy material than originally assumed, which suggests that Uranus and Neptune’s progenitors wouldn’t have been so ice-rich, either. Second, our understanding of how “rocky” materials respond at the temperatures and pressures found in these planet interiors has evolved. In particular, silicate, hydrogen, and iron are actually miscible at these conditions. That means that discrete sub-layers separated by material type are not as likely.

    Using the magma ocean model, the team found compositions for both Uranus and Neptune that conformed well to our limited data about their gravitational and magnetic field properties. Time–and more data–will tell as to which interior model best describes these enigmatic giants. (Image credit: NASA; research credit: E. Young et al. (preprint); via Gizmodo)

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