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Search results for: “jet”

  • Coriolis

    Coriolis

    There’s an infamous supposition about drains swirling one way in the Northern Hemisphere and the other way in the Southern Hemisphere. Destin from Smarter Every Day and Derek from Veritasium have put the claim to the test with experiments on either side of the globe. First, go here and watch their synchronized videos side-by-side. (To synchronize, start the left video and pause it at the sync point. Then start the second video and unpause the first video when the second video hits the sync point.) I’ll wait here.

    …

    That was awesome, right?! The demonstration doesn’t work with toilets because they’re driven by the placement of jets around the circumference. And your bathtub doesn’t usually work either because any residual vorticity in the tub gets magnified by conservation of angular momentum as it drains. It’s like a spinning ice skater pulling their arms in; the rotation speeds up. So, to get around that problem, Destin and Derek let their pools sit for a day to damp out any motion before draining. At that point, the Coriolis effect is strong enough to cause the pools to rotate in opposite directions when drained. You may wonder why the effect is so slight for the pools when it’s pretty stark with hurricanes and cyclones. The answer is a matter of scale. The pools are perhaps 2 meters wide, which means that the difference in latitude across the the pool is very slight and therefore, the differential speed imparted by the Earth’s rotation is also very small. Because hurricanes and cyclones are much larger, they experience stronger influence from the Coriolis effect. (Image credits: Smarter Every Day/Veritasium; via It’s Okay To Be Smart)

  • Jumps in Stratified Flows

    Jumps in Stratified Flows

    One of the factors that complicates geophysical flows is that both the atmosphere and the ocean are stratified fluids with many stacked layers of differing densities. These variations in density can generate instabilities, trap rising or sinking fluids, and transmit waves. The animations above show flow over two ridges with dye visualization (top), velocity (middle), and contours of density (bottom). The upstream influence of the left ridge creates a smooth, focused flow that quickly becomes turbulent after the crest. The jet rebounds as a turbulent hydraulic jump before slowing again upstream of the second ridge. Like the first ridge, the second ridge also generates a hydraulic jump on the lee side. Clearly both stratification and the local topography play a big role in how air moves over and between the ridges. If prevailing winds favor these kinds of flows, it can help generate local microclimates. (Image credit and submission: K. Winters, source videos)

  • 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)

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    Fire-Breathing

    In this high-speed video, the Slow Mo Guys demonstrate fire-breathing. Rather than using a liquid fuel like kerosene, they utilize cornstarch, which is both easily flammable and non-volatile thanks to its powdered form. Blowing out the cornstarch creates a turbulent jet of cornstarch and air. Combine that with a combustion source, and the cornstarch quickly deflagrates, meaning that the flame propagates via heat transfer. When neighboring regions of cornstarch become hot enough, they ignite and the flame front expands. You can observe this in the flame growth shown in the video; just after ignition the cornstarch jet is much wider than the fire and it takes some time for the flames to catch up with the jet. Although a liquid-fueled fireball operates by the same principles, it can look rather different. For comparison, check out this high-speed video of a WD-40 fireball. And, hopefully it goes without saying, but don’t try this stuff at home. (Video credit: The Slow Mo Guys)

  • Hand Dryers and Atomization

    Hand Dryers and Atomization

    Some newer electric hand dryers, like the Dyson Airblade, use jets of high-speed air to dry hands faster than traditional models. Much of their effectiveness comes from the rapid atomization–or break-up into tiny droplets–of water on one’s hands. This is demonstrated in the animation above, which comes from a high-speed video of a water drop falling through the jets of a homemade dryer. Breaking up the water quickly disperses the microdroplets but it also speeds up evaporation by greatly increasing the exposed surface area of the water. This is similar to how you can get instant snow from throwing boiling water if it’s cold enough outside. (Image credit: tesla500, source video; submitted by Nick)

  • Viscous Droplet Impacts

    Viscous Droplet Impacts

    Viscosity can have a notable effect on droplet impacts. This poster demonstrates with snapshots from three droplet impacts. The blue drops are dyed water, and the red ones are a more viscous water-glycerol mixture. When the two water droplets impact, a skirt forms between them, then spreads outward into a sheet with a thicker, uneven rim before retracting. The second row shows a water droplet impacting a water-glycerol droplet. The less viscous water droplet deforms faster, wrapping around and mixing into the other drop before rebounding in a jet. The last row switches the impacts, with the more viscous drop falling onto the water. As in the previous case, the water deforms faster than the water-glycerol. The two mix during spreading and rebound slower. In the last timestep shown, the droplet is still contracting, but it does rebound as a jet thereafter. (Image credit: T. Fanning et al.)

  • Cavitation

    [original media no longer available]

    Cavitation–the formation and collapse of vapor-filled cavities within a liquid–occurs in a variety of natural and manmade applications. It can shatter bottles, wreak havoc with boat impellers, is used as a hunting mechanism by several shrimp species, and can even generate light and sound. It is the collapse of the cavitation bubble that can be so damaging, and this video shows how. In the experiment, researchers generate a cavitation bubble near the free surface–or, in other words, near the air-water interface. Pressure in the bubble is much lower than the pressure of the surrounding liquid, so the bubble collapses after the momentum from its initial generation is spent. Interaction with the surface generates a jet that projects downward and pierces the cavitation bubble as it collapses. As seen from 0:54 onward, the bubble’s collapse generates a shock wave that propagates outward from the bubble site. It’s this shock wave that so effectively damages materials and stuns underwater prey. (Video credit: O. Supponen et al.)

  • Beverage Bubbles Bursting

    Beverage Bubbles Bursting

    Fizzy drinks like soda and champagne have many bubbles which rise to the surface before bursting. When the film separating the bubble and the air drains and bursts, it leaves a millimeter-sized cavity that collapses on itself. That collapse creates an upward jet of fluid which can break into tiny aerosol droplets that disperse the aroma and flavor of the drink. Similar bubble-bursting events occur in sea spray and industrial applications, too. Researchers find that droplet ejection depends on bubble geometry and fluid properties such as viscosity. More viscous liquids, for example, generate smaller and faster droplets. Learn more and see videos of bubble-bursts at Newswise. (Image credit: E. Ghabache 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)

  • The Kaye Effect

    The Kaye Effect

    Those who have poured viscous liquids like syrup or honey are familiar with how they stack up in a rope-like coil, as shown in the top row of images above. What is less familiar, thanks to the high speed at which it occurs, is the Kaye effect, which happens in fluids like shampoo when drizzled. Shampoo is a shear-thinning liquid, meaning that it becomes less viscous when deformed. Like a normal Newtonian fluid, shampoo first forms a heap (bottom row, far left). But instead of coiling neatly, the heap ejects a secondary outgoing jet. This occurs when a dimple forms in the heap due to the impact of the inbound jet. The deformation causes the local viscosity to drop at the point of impact and the jet slips off the heap. The formation is unstable, causing the heap and jet to collapse in just a few hundred milliseconds, at which point the process begins again. (Image credit: L. Courbin et al.)

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