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  • Beneath the Cavity

    Beneath the Cavity

    When a drop falls into a pool of liquid, it creates a distinctive cavity, followed by a jet. From above the surface, this process is well-studied. But this poster offers us a glimpse of what goes on beneath the surface, using particle image velocimetry. This technique follows the paths of tiny particles in the fluid to reveal how the fluid moves.

    As the cavity grows, fluid is pushed away. But the cavity’s reversal comes with a change in flow direction. The arrows now point toward the shrinking cavity — and they’re much larger, indicating a strong inward flow. It’s this convergence that creates the Worthington jet that rebounds from the surface. And, as the jet falls back, its momentum gets transferred into a vortex ring that drifts downward from the point of impact. (Image credit: R. Sharma et al.)

  • A Starry Nursery

    A Starry Nursery

    This mountain of interstellar gas and dust lies in the picturesque Eagle Nebula. Though it appears solid in this near-infrared image from JWST, the density of the structure is actually quite low. Jets and solar winds from the glowing, young stars inside the region sculpt the pillar’s shape. Over the next 100,000 years, the stars’ energetic jets, solar winds, and destructive supernovas will destroy the dusty nursery. (Image credit: NASA/ESA/CSA/STScI/M. Özsaraç)

  • Founts of Enceladus

    Founts of Enceladus

    In its exploration of Saturn, Cassini discovered that the moon Enceladus is home to icy eruptions. Beneath its shell of ice, Enceladus has a global ocean of salty liquid water. The average thickness of the ice is 20 kilometers, putting the ocean seemingly out of reach — except at the moon’s southern pole, where icy plumes of ocean water jet out.

    Here, where the ice is thinnest, the tidal forces Enceladus experiences from Saturn and its fellow moon Dione break through the ice. As the cracks open and close, liquid from the ocean sprays out, freezing into plumes that Cassini measured. Plans are underway for new missions that prioritize further sampling of Enceladus’ ocean. For now, we can only imagine what hides in its interior ocean. (Image credit: NASA/JPL-Caltech/SSI; for more, see M. Manga and M. Rudolph)

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    Hollow Drops

    When a partially-air-filled drop hits a surface, it splashes and rebounds in a complex fashion. This video breaks down the physics of the process. Upon impact, a lamella spreads, eventually becoming wavy and unstable along its rim. At the same time, a counterjet forms, growing until it pierces the remaining bubble of the drop. The jet continues to stretch upward due to its momentum, pinching off and forming wobbly satellite drops that finally fall back to the surface. (Image and video credit: D. Naidu and S. Dash)

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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.)

  • Airflow in the Opera

    Airflow in the Opera

    Like so many other performers, the singers and musicians of New York’s Metropolitan Opera House were left without a way to safely perform when the SARS-CoV-2 pandemic began in early 2020. In search of safe ways to perform and rehearse, the Met turned to researchers at nearby Princeton University, who worked directly with the performers to explore aerosol production and airflow in the context of professional opera.

    Through visualization and other experiments, the team found that the highly-controlled breathing of opera singers actually posed a lower risk for spreading pathogens than typical speaking and breathing. Most of a singer’s voiced sounds are sustained vowels, which produce a slow, buoyant jet that remains close to a singer. The exception are consonants, which created rapid, forward-projected jets.

    In the orchestra, the researchers found that placing a mask over the bell of wind instruments like the trombone reduced the speed and spread of air. One of the highest risk instruments they found was the oboe. Playing the oboe requires a long, slow release of air, but between musical phrases, oboists rapidly exhale any remaining air from their lungs and take a fresh breath. That rapid exhale creates a fast, forceful jet of air that necessitates placing the oboist further from others. (Image credit: top – P. Chiabrando, others – P. Bourrianne et al.; research credit: P. Bourrianne et al.; via APS Physics; submitted by Kam-Yung Soh)

  • Never Break the Chain

    Never Break the Chain

    Pour water out of a bottle, and you’ll see a jet with a shape that resembles chain links. Sometimes known as a “liquid chain,” this phenomenon occurs when water pours through a non-circular hole. It’s quite a complex behavior, as shown in this recent study of the nonlinear effect. Even so, the authors found that the amplitude and wavelength of the chain’s sections are tied directly to the shape of the opening. Current models of the effect don’t account for the viscosity of the liquid, though, so future experiments will have to explore how fluids other than water behave. (Image and research credit: D. Jordan et al.; via APS Physics; submitted by Kam-Yung Soh)

    A comparison of oscillating jet shapes and metal chains.
    A comparison of an oscillating jet’s shape and metal chains. Each view is rotated 45 degrees from the one before.
  • Testing Full-Size Engines

    Testing Full-Size Engines

    Engineers can often use small-scale models to test the physics of their creations, but sometimes there’s no substitute for going large. In this photo, we see a full-size commercial engine used on an airplane, mounted at the Instituto Nacional de Tecnica Aeroespacial (INTA) in Madrid.

    Behind the engine, in red, is an optical rig used for a brand-new measurement technique that allows engineers to directly measure the carbon dioxide emissions of the engine as it runs. The optical frame is 7 meters in diameter and uses 126 beams of near-infrared laser light to probe the engine’s exhaust without interrupting the flow. It’s the first chemically specific imaging of a full-scale gas turbine like those found on commercial aircraft. Given the high carbon emissions associated with air travel, the technique will be important for engineers building greener aircraft engines. (Image and research credit: A. Upadhyay et al.; via The Engineer; submitted by Simon H.)

  • “Keeping Our Sheet Together”

    “Keeping Our Sheet Together”

    When two liquid jets collide, they form a falling liquid sheet. Here researchers explore how that sheet breaks up when the liquids involved contain polymers. The intact areas of the sheet show as dark red or almost black. The edges of the sheet appear in brighter red and yellow, outlining the holes that form and grow during breakup. The type of breakup observed depends on the concentration of polymer in the liquid. (Image credit: C. Galvin et al.)

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    Pistol Shrimp Snaps

    Gram for gram, few animals can match the power of a pistol shrimp’s snap. When its claw closes, the shrimp ejects a jet of water so fast that the water pressure drops below the vapor pressure, causing a cavitation bubble. Like other cavitation bubbles, this one is short-lived, growing and collapsing (and sending out shock waves!) in less than a millisecond. That’s enough to knock any predator or prey for a loop. (Image and video credit: Ant Lab)

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