FYFD

Tag: fluid dynamics

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    “The Ballet of Colors”

    Thomas Blanchard’s short film “The Ballet of Colors” plunges viewers into a warm spectrum of roiling oil and paint. Fluid dynamically speaking, it could be subtitled “the Plateau-Rayleigh instability” thanks to its focus on retracting paint ruptures and ligaments breaking into droplets. Unlike some other videos of this genre, Blanchard uses a high-speed camera here, filming the action at 1,000 frames per second, and the result is smooth, crisply focused, and absolutely delectable. (Video and image credit: T. Blanchard et al.)

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  • Filtering by Sea Sponge

    Filtering by Sea Sponge

    Gathering oil after a spill is fiendishly difficult. Deploying booms to corral and soak up oil at the water surface only catches a fraction of the spill. A recent study instead turns to nature to inspire its oil filter. The team was inspired by the Venus’ flower basket, a type of deep-sea sponge with a multi-scale structure that excels at pulling nutrients out of complex flow fields. The outer surface of the sponge has helical ridges that break up the turbulence of any incoming flow, helping the sponge stay anchored by reducing the force needed to resist the flow. Beneath the ridges, the sponge’s skeleton has a smaller, checkered pattern that further breaks up the flow as it enters into the sponge’s hollow body. Within this cavity, the flow is slower and swirling, giving plenty of time for nutrients in the water to collide with the nutrient-gathering flagellum lining the sponge.

    By mimicking this three-level structure, the team built a capable oil-capturing device that can filter even emulsified oil from the water. They swapped the flagellum with a (replaceable) oil-adsorbing material and found that their filter captured more than 97% of oil across a range of flow conditions. (Image credit: NOAA; research credit: Y. Yu et al.; via Physics World)

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    Salt Affects Particle Spreading

    Microplastics are proliferating in our oceans (and everywhere else). This video takes a look at how salt and salinity gradients could affect the way plastics move. The researchers begin with a liquid bath sandwiched between a bed of magnets and electrodes. Using Lorentz forcing, they create an essentially 2D flow field that is ordered or chaotic, depending on the magnets’ configuration. Although it’s driven very differently, the flow field resembles the way the upper layer of the ocean moves and mixes.

    The researchers then introduce colloids (particles that act as an analog for microplastics) and a bit of salt. Depending on the salinity gradient in the bath, the colloids can be attracted to one another or repelled. As the team shows, the resulting spread of colloids depends strongly on these salinity conditions, suggesting that microplastics, too, could see stronger dispersion or trapping depending on salinity changes. (Video and image credit: M. Alipour et al.)

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  • Derecho-Induced Skyscraper Damage

    Derecho-Induced Skyscraper Damage

    Derechos are short-lived, intense wind storms sometimes associated with thunderstorms. Last spring, such a storm passed through Houston, leaving downtown skyscrapers with more damage than a hurricane with comparable wind speeds. Now researchers believe they know why a derecho’s 40 meter per second winds can badly damage buildings built to withstand 67 meter per second hurricane winds.

    In surveying the damage to Houston’s skyscrapers, the team noted that broken windows were concentrated in areas that faced other tall buildings. In a wind facility, the team explored how skyscrapers interfered with each other, based on their separation difference. They looked both at conditions that mimicked a hurricane’s winds as well as the downbursts — strong downward wind bursts — that are found in derechos.

    The researchers found that downbursts in between nearby buildings caused extremely strong suction forces along a building’s face — even compared to the forces seen with higher hurricane-force winds. Currently, these buildings are designed for hurricane-like conditions, but the team suggests that — at least in some regions — designers will need to take into account how downburst wind patterns affect a skyscraper, too. (Image credit: National Weather Service; research credit: O. Metwally et al.; via Ars Technica)

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    Seeing Sound

    Sound, vibration, and motion are all inextricably linked. In this BBC video, physicist Helen Czerski shows how an object’s sound and vibrations relate through the classic Chladni experiment. She vibrates a metal plate scattered with sand. At most vibration frequencies, the particles of sand bounce all over the place with no distinctive pattern. But at an object’s natural frequencies, there are standing waves and the sand gathers in spots where the standing wave has no vertical motion. The higher the vibration frequency, the more complex the pattern the sand makes. All of this plays into the sounds we hear, too. When struck, an object vibrates at many of its natural frequencies at once. That’s what gives us a rich, musical tone — all those layered frequencies. (Video and image credit: BBC)

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  • “Skimming the Waves”

    “Skimming the Waves”

    Common terns are gregarious sea birds that cruise low over the water to fish. When they spot prey, they will dip down to grab a fish from the surface, or they will fold their wings to plunge-dive to depths of half a meter. Compared to gannets and boobies, these are slower, shallower dives that involve less impact risk. Presumably the birds’ choice of dive height reflects the typical swim depth of their preferred fish. (Image credit: N. Kovo/WPOTY; via Colossal)

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  • Ultra-Soft Solids Flow By Turning Inside Out

    Ultra-Soft Solids Flow By Turning Inside Out

    Can a solid flow? What would that even look like? Researchers explored these questions with an ultra-soft gel (think 100,000 times softer than a gummy bear) pumped through a ring-shaped annular pipe. Despite its elasticity — that tendency to return to an original shape that distinguishes solids from fluids — the gel does flow. But after a short distance, furrows form and grow along the gel’s leading edge.

    Front view of an ultra-soft solid flowing through an annular pipe. The furrows forming along the face of the gel are places where the gel is essentially turning itself inside out.
    Front view of an ultra-soft solid flowing through an annular pipe. The furrows forming along the face of the gel are places where the gel is essentially turning itself inside out.

    Since the gel alongside the pipe’s walls can’t slide due to friction, the gel flows by essentially turning itself inside out. Inner portions of the gel flow forward and then split off toward one of the walls as they reach the leading edge. This eversion builds up lots of internal stress in the gel, and furrowing — much like crumpling a sheet of paper — relieves that stress. (Image and research credit: J. Hwang et al.; via APS News)

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    Strandbeest Evolution

    Theo Jansen’s Strandbeests are massive, wind-powered kinetic sculptures designed to roam Dutch beaches. Conceived in the late 1980s as a way to kick up sand that would replenish nearby dunes, the beests have grown into a decades-long obsession for the artist and his followers. This Veritasium video charts the development and evolution of the Strandbeest from its original concept through Jansen’s increasingly self-sufficient versions. I found the leg linkage of the Strandbeest especially fascinating. How neat to find a relatively simply proportion of linkages capable of turning a small crank’s motion into a stable walking gait. Anyone else feel like building a miniature Strandbeest now? (Video and image credit: Veritasium)

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  • Anti-Icing Polar Bear Fur

    Anti-Icing Polar Bear Fur

    Despite spending their lives in and around frigid water, snow, and ice, polar bears are rarely troubled by ice building up on their fur. This natural anti-icing property is one Inuits have long taken advantage of by using polar bear fur in hunting stools and sandals. In a new study, researchers looked at just how “icephobic” polar bear fur is and what properties make it so.

    The key to a polar bear’s anti-icing is sebum — a mixture of cholesterol, diacylglycerols, and fatty acids secreted from glands near each hair’s root. When sebum is present on the hair, the researchers found it takes very little force to remove ice; in contrast, fur that had been washed with a surfactant that stripped away the sebum clung to ice.

    The researchers are interested in uncovering which specific chemical components of sebum impart its icephobicity. That information could enable a new generation of anti-icing treatments for aircraft and other human-made technologies; right now, many anti-icing treatments use PFAS, also known as “forever chemicals,” that have major disadvantages to human and environmental health. (Image credit: H. Mager; research credit: J. Carolan et al.; via Physics World)

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  • A Drop’s Shape Effects

    A Drop’s Shape Effects

    Falling raindrops get distorted by the air rushing past them, ultimately breaking large droplets into many smaller ones. This research poster shows how variable this process is by showing two different raindrops, both of the same 8-mm initial diameter. On the left, the drop is prolate — longer than it is wide — and on the right, the drop is oblate — wider than it is long. Moving from bottom to top, we see a series of snapshots of each drop’s shape as it deforms and, eventually, breaks into smaller drops. The overall process is similar for each: the drop flattens, dimples, and then inflates like a sail, with part of the drop thinning into a sheet and ultimately breaking into smaller droplets. Yet, each drop’s specific details are entirely different. (Image credit: S. Dighe et al.)

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