FYFD

Tag: fluid dynamics

  • Measuring Mucus by Dragging Dead Fish

    Measuring Mucus by Dragging Dead Fish

    A fish‘s mucus layer is critical; it protects from pathogens, reduces drag in the water, and, in some cases, protects against predators. But little is known about how mucus could affect terrestrial locomotion in species like the northern snakehead, which can breathe out of the water and move across land. So researchers explored the snakehead’s mucus layer by measuring the force required to drag them (and two other non-terrestrial species) across different surfaces.

    The team tested the same, freshly euthanized fish twice: once with its mucus layer intact and again once the mucus was washed off. Unsurprisingly, the fish’s friction was much lower with its mucus. But they also found that the snakehead was slipperier than either the scaled carp or the scale-free catfish. The biologists suggest that the snakehead could have evolved a slipperier mucus to help it move more easily on land, thereby extending the distance it can cover.

    As a fluid dynamicist, I think fish mucus sounds like a great new playground for the rheologists among us. (Image and research credit: F. Lopez-Chilel and N. Bressman; via PopSci)

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    Chaotic Hose Instability

    Steve Mould is back with another video looking at wild fluid behaviors. This time he’s considering hose instabilities like the one that makes a water-carrying hose beyond a certain length to whip wildly back and forth. He tries to track down the reasoning for these flexible hoses snapping and whipping. In truth, both the hoses and the wind dancers do their thing due to interactions between the elasticity of the hose and the fluid dynamics of the flows within. These applications are ripe for a few control volume thought experiments. (Video and image credit: S. Mould)

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  • Reclaiming the Land

    Reclaiming the Land

    Lava floods human-made infrastructure on Iceland’s Reykjanes peninsula in this aerial image from photographer Ael Kermarec. Protecting roads and buildings from lava flows is a formidable challenge, but it’s one that researchers are tackling. But the larger and faster the lava flow, the harder infrastructure is to protect. Sometimes our best efforts are simply overwhelmed by nature’s power. (Image credit: A. Kermarec/WNPA; via Colossal)

  • Thawing Permafrost Primes Slumps

    Thawing Permafrost Primes Slumps

    As permafrost thaws on Arctic hillsides and shorelines, the land often deforms in a unique fashion, known as a slump. Formally known as mega retrogressive thaw slumps, these areas superficially resemble a landslide. They’re also prone to repeat performances: as many as 90% of Canada’s Arctic slumps recur in the same place as previous slumps. Researchers used ground-penetrating radar and other tools to study the underground structure at slumps and found that several factors contribute to this repetitive cycle.

    Seawater soaking into the foot of a hilly shore can destabilize the permafrost, creating a slump. That changes the nearby ground cover, exposing more permafrost to warming; their measurements showed this warming could extend tens of meters underground, priming the area for future slumps. Similarly, the mudslides and narrow ravines that form on an active slump also shift away ground cover and warm the underlying permafrost. Together, these factors suggest that once a slump forms, more slumps will occur as the underlying permafrost warms. (Image credit: M. Krautblatter; research credit: M. Krautblatter et al.; via Eos)

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    Twisting in the Flow

    What happens to liquid crystals in a flow? In this video, researchers look at liquid crystals flowing through the narrow gap of a microfluidic device. Initially, all the crystals are oriented the same way, as if they are logs rolling down a river. But as the flow rate increases, narrow lines appear in the flow, followed by disordered regions, and, eventually, a new configuration: vertical bands streaking the left-to-right flow. The colors, in this case, indicate the orientation of the liquid crystals. As the researchers show, the crystals collectively twist to form the spontaneous bands. (Video and image credit: D. Jia and I. Bischofberger)

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  • Simulating a Sneeze

    Simulating a Sneeze

    Sneezing and coughing can spread pathogens both through large droplets and through tiny, airborne aerosols. Understanding how the nasal cavity shapes the aerosol cloud a sneeze produces is critical to understanding and predicting how viruses could spread. Toward that end, researchers built a “sneeze simulator” based on the upper respiratory system’s geometry. With their simulator, the team mimicked violent exhalations both with the nostrils open and closed — to see how that changed the shape of the aerosol cloud produced.

    The researchers found that closed nostrils produced a cloud that moved away along a 18 degree downward tilt, whereas an open-nostril cloud followed a 30-degree downward slope. That means having the nostrils open reduces the horizontal spread of a cloud while increasing its vertical spread. Depending on the background flow that will affect which parts of a cloud get spread to people nearby. (Image and research credit: N. Catalán et al.; via Physics World)

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  • Growing Ice

    Growing Ice

    While much attention is given to the summer loss of sea ice, the birth of new ice in the fall is also critical. Ice loss in the summer leaves oceans warmer and waves larger since wind can blow across longer open stretches. Those warmer waters and more dynamic waves affect how ice forms once autumn sets in. Higher waves mean that ice tends to form in “pancakes” like those seen here. Pancake ice is small — typically under 1 meter wide — and can only be observed from nearby, since they’re smaller than typical satellite resolution. Only once there’s enough pancake ice to dampen the waves will the pieces begin to cement together to form larger pieces that will form the basis of the year’s new ice. (Image credit: M. Smith; see also Eos)

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  • “Visions in Ice”

    “Visions in Ice”

    The glittering blue interior of an ice cave sparkles in this award-winning image by photographer Yasmin Namini. The cave is underneath Iceland’s Vatnajokull Glacier. Notice the deep scallops carved into the lower wall. This shape is common in melting and dissolution processes. It is unavoidable for flat surfaces exposed to a melting/dissolving flow. (Image credit: Y. Namini/WNPA; via Colossal)

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  • Crowd Vortices

    Crowd Vortices

    The Feast of San Fermín in Pamplona, Spain draws crowds of thousands. Scientists recently published an analysis of the crowd motion in these dense gatherings. The team filmed the crowds at the festival from balconies overlooking the plaza in 2019, 2022, 2023, and 2024. Analyzing the footage, they discovered that at crowd densities above 4 people per square meter, the crowd begins to move in almost imperceptible eddies. In the animation below, lines trace out the path followed by single individuals in the crowd, showing the underlying “vortex.” At the plaza’s highest density — 9 people per square meter — one rotation of the vortex took about 18 seconds.

    Animation of the crowd in motion, with overlaid lines showing the circulating path followed by individual crowd members.

    The team found similar patterns in footage of the crowd at the 2010 Love Parade disaster, in which 21 people died. These patterns aren’t themselves an indicator of an unsafe crowd — none of the studied Pamplona crowds had a problem — but understanding the underlying dynamics should help planners recognize and prevent dangerous crowd behaviors before the start of a stampede. (Image credit: still – San Fermín, animation – Bartolo Lab; research credit: F. Gu et al.; via Nature)

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  • A Stellar Look at NGC 602

    A Stellar Look at NGC 602

    The young star cluster NGC 602 sits some 200,000 light years away in the Small Magellanic Cloud. Seen here in near- and mid-infrared, the cluster is a glowing cradle of star forming conditions similar to the early universe. A large nebula, made up of multicolored dust and gas, surrounds the star cluster. Its dusty finger-like pillars could be an example of Rayleigh-Taylor instabilities or plumes shaped by energetic stellar jets. (Image credit: NASA/ESA/CSA/JWST; via Colossal)

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