FYFD

Tag: jets

  • Miniature Bursting Bubbles

    Miniature Bursting Bubbles

    Fizzy drinks like soda or champagne contain dissolved carbon dioxide which forms bubbles when the pressure inside its container is released. The tiny bubbles rise to the surface where the liquid film covering them can rupture, creating a small cavity at the surface. The cavity collapses in a matter of milliseconds (bottom animation). Above the surface, the cavity reverses its curvature to create a liquid jet (top animation) which can expel multiple tiny droplets. These droplets can tickle a drinker who hovers too close, but they also carry and distribute the aroma molecules that are part of the experience of a drink like champagne. (Image credit: E. Ghabache et al., source)

    (Today’s topic brought to you by my impending nuptials to my favorite physicist/spacecraft engineer.)

  • The Dance of the Droplets

    The Dance of the Droplets

    Milk and juice vibrating on a speaker can put on a veritable fireworks display of fluid dynamics. Vibrating a fluid can cause small standing waves, called Faraday waves, on the surface of the fluid. Add more energy and the instabilities grow nonlinearly, quickly leading to tiny ligaments and jets of liquid shooting upward. With sufficiently high energy, the jets shoot beyond the point where surface tension can hold the liquid together, resulting in a spray of droplets. (Image credit: vurt runner, source video; h/t to @jchawner)

  • Jet Impact

    Jet Impact

    Viscoelasticity can generate some bizarre fluid behaviors. Viscoelastic fluids are special class of non-Newtonian fluid in which the response to deformation is both viscous, like a fluid, and elastic, like rubber. Above, a jet of viscoelastic fluid impacts a plate as viewed from the side (top image) and beneath (bottom image). When the jet impacts the plate, elastic stresses in the fluid destabilize the cylindrical symmetry of the jet. The jet instead becomes webbed, with an odd, asymmetric number of webs. The number of webs depends on the viscoelastic properties of the fluid as well as the jet’s speed and distance from the plate. (Image credit: B. Néel et al.)

  • Turbulence and Star Formation

    Turbulence and Star Formation

    Galaxy clusters are objects containing hundreds or thousands of galaxies immersed in hot gas. This gas glows brightly in X-ray, as seen in the Perseus (top) and Virgo (bottom) clusters above. Over time, the gas near the center of the clusters should cool, generating many new stars, but this is not what astronomers observe. New research suggests turbulence may prevent this star formation. The supermassive black holes near the center of these galaxy clusters pump enormous amounts of energy into their surroundings through jets of particles. Those jets churn the gas of the cluster, generating turbulence, which ultimately dissipates as heat. It is this turbulent heating astronomers think counters the radiative cooling of the gas, thereby keeping the gas hot enough to prevent star formation. You can read more about the findings in the research paper.  (Image credits: NASA/Chandra/I. Zhuravleva et al.; via io9)

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    The Archer Fish’s Arrow

    Archer fish hunt by shooting jets of water at their prey to knock them into the water where the fish can eat them. Previous research showed that the archer fish’s projectile jet is pulsed such that the water released at a later time has a greater velocity. This makes the jet bunch up so that a ball of liquid hits the prey with greater force than the jet would otherwise. A recently released paper shows that the archer fish actively adjust their liquid jets in order to strike targets at different distances while maintaining this bunching effect. To control the jets, the fish adjust both how long they jet and what speed they impart to the fluid by changing how they open and close their mouths. (VIdeo credit: Nature; research credit: P. Gerullis and S. Schuster; via phys.org; submitted by @jchawner)

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    The Physics of Sneezing

    Sneezing can be a major factor in the spread of some illnesses. Not only does sneezing spew out a cloud of tiny pathogen-bearing droplets, but it also releases a warm, moist jet of air. Flows like this that combine both liquid and gas phases are called multiphase flows, and they can be a challenge to study because of the interactions between the phases. For example, the buoyancy of the air jet helps keep smaller droplets aloft, allowing them to travel further or even get picked up and spread by environmental systems. Researchers hope that studying the fluid dynamics and mathematics of these turbulent multiphase clouds will help predict and control the spread of pathogens. Check out the Bourouiba research group for more. (Video credit: Science Friday)

  • Bioluminescence

    Bioluminescence

    In the dark of the ocean, some animals have evolved to use bioluminescence as a defense. In the animation above, an ostracod, one of the tiny crustaceans seen flitting near the top of the tank, has just been swallowed by a cardinal fish. When threatened, the ostracod ejects two chemicals, luciferin and luciferase, which, when combined, emit light. Because the glow would draw undesirable attention to the cardinal fish, it spits out the ostracod and the glowing liquid and flees. Check out the full video clip over at BBC News. Other crustaceans, including several species of shrimp, also spit out bioluminescent fluids defensively. (Image credit: BBC, source video; via @amyleerobinson)

  • Inside a Rocket

    Inside a Rocket

    Rockets often utilize liquid propellants for their combustion. To maximize the efficiency during burning, the liquid fuel and oxidizer must mix quickly and break up into an easily vaporized spray. One method to achieve this is to inject the fuel and oxidizer as liquid jets that collide with one another. For high enough flow rates, this creates a highly unstable liquid sheet that quickly atomizes into a spray of droplets. The animation above shows an example of two impinging jets, but rockets using this method would typically have more than just two injection points. Other rockets use co-axial or centrifugal injectors to mix and atomize the fuel and oxidizer prior to combustion.  (Image credit: C. Inoue; full-scale GIF)

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    Granular Jets

    Object impacts in water and other fluids often create cavities that generate jets when they collapse. But impacts on granular materials can produce similar results, forming a cavity, a splash corona, and, under the right circumstances, a jet. This Sixty Symbols video explores the effect of grain size (and thus weight) on the formation of such a rebound jet. Ultimately, the jet behavior is driven by air. When the granular material is poured, air gets trapped between the grains. The impact compresses the grains, forcing the previously trapped air up and out through the cavity created by the impact. Interestingly, once the air pressure is low enough, jet creation is suppressed, not unlike splash suppression in liquids. (Video credit: Sixty Symbols/Univ. of Nottingham)

  • Forming a Jet

    Forming a Jet

    Many situations can generate high-speed liquid jets, including droplet impacts, vibrated fluids, and surface charges. In each of these cases, a concave liquid surface is impulsively accelerated, which causes the flow to focus into a jet. The image above shows snapshots of a microjet generated from a 50 micron capillary tube visible at the right. This jet formed when the meniscus inside the capillary tube was disturbed by a laser pulse that vaporized fluid behind the interface. Incredibly, the microjets generated with this method can reach speeds of 850 m/s, nearly 3 times the speed of sound in air. Researchers have found the method produces consistent results and suggest that it could one day form the basis for needle-free drug injection. You can read more in their freely available paper. (Photo credit: K. Tagawa et al.)