FYFD

Tag: Worthington jet

  • Reader Question: Splashes

    Reader Question: Splashes

    Reader effjoebiden asks:

    So is the crown splash the curving wave of water on either side of the tire, the spikes of water in the middle behind the tire, or both? And is the Worthington jet also the same phenomenon that can happen with a massive meteorite impact?

    Here the term “crown splash” refers to the curving sheets of water spreading on either side of the tire. Those liquid sheets (or lamella) break down at the edges into spikes and droplets just like the ones seen when a drop falls into a pool, which is the traditional source of the term “crown splash” because it resembles a crown.

    And, yes, enormous meteor impacts can create Worthington jets (that column of fluid that pops up after a droplet impacts)! This is why some craters have peaks in the middle. There are actually some surprising similarities between meteor impacts and fluid dynamics.

    (Image credits: S. Reckinger et al., original post)

  • Daily Fluids, Part 4

    Daily Fluids, Part 4

    Inside or outside, we encounter a lot of fluid dynamics every day. Here are some examples you might have noticed, especially on a rainy day:

    Worthington Jets
    After a drop falls into a pool, there’s a column-like jet that pops up after it and sometimes ejects another small drop. This is known to fluid dynamicists as a Worthington jet, but really it’s something we all see regularly, especially if you watch rain falling onto puddles or look really closely at your carbonated drink.

    Crown Splash
    Like the Worthington jet, crown splashes often follow a drop’s impact into another liquid. But they can also show up when slicing or stomping through puddles!

    Free Surface Dynamics
    Anytime you have a body of water in contact with a body of air, fluid dynamicists call that a free surface. How the interface between the two fluids shifts and transforms is fascinating and complicated. Waterfalls are a great example of this, but so are ocean waves or even the ripples from tossing a rock into a pond.

    Hydrophobic Surfaces
    Water-repellent surfaces are called hydrophobic. Water will bead up on the surface and roll off easily. While many manmade surfaces are hydrophobic, like the teflon in your skillet, so are many natural surfaces. Many leaves are hydrophobic because plants want that water to fall to the ground where their roots can soak it up. Keep an eye out as you wash different vegetables and fruits and see which ones are hydrophobic!

    Check out all of this week’s posts more examples of fluid dynamics in daily life. (Image credit: S. Reckinger et al., source)

  • Raindrops in Puddles

    Raindrops in Puddles

    Watching rain drops hit a puddle or lake is remarkably fascinating. Each drop creates a little cavity in the water surface when it impacts. Large, energetic drops will create a crown-shaped splash, like the ones in the upper animation. When the cavity below the surface collapses, the water rebounds into a pillar known as a Worthington jet. Look carefully and you’ll see some of those jets are energetic enough to produce a little satellite droplet that falls back and coalesces. Altogether it’s a beautifully complex process to watch happen over and over again. (Image credit: K. Weiner, source)

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  • Liquid Umbrella

    Liquid Umbrella

    When a water drop strikes a pool, it can form a cavity in the free surface that will rebound into a jet. If a well-timed second drop hits that jet at the height of its rebound, the impact creates an umbrella-like sheet like the one seen here. The thin liquid sheet expands outward from the point of impact, its rim thickening and ejecting tiny filaments and droplets as surface tension causes a Plateau-Rayleigh-type instability. Tiny capillary waves–ripples–gather near the rim, an echo of the impact between the jet and the second drop. All of this occurs in less than the blink of an eye, but with high-speed video and perfectly-timed photography, we can capture the beauty of these everyday phenomena. (Photo credit: H. Westum)

  • Liquid Sculptures

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    Water sculptures–a marriage of liquids, photography, and timing–are spectacular form of fluid dynamics as art. Artist Markus Reugels is a master of the form. This video captures the life and death of such water sculptures at 2,000 fps, beginning with the fall of the initial blue droplet. The droplet’s impact causes a rebounding Worthington jet, which reaches its pinnacle just as a second droplet strikes. The impact spreads into an umbrella-like skirt consisting of a thin, expanding liquid sheet with a thicker rim. The rim itself is unstable, breaking into regularly spaced filaments and tiny satellite droplets that shoot outward before the entire structure collapses into the pool. One especially cool aspect of watching this in video is seeing how the blue dye from each droplet spreads as the water splashes and rebounds. You can see the set-up Reugels uses for his photography here. (Video credit: M. Reugels and L. Lehner)

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    Reader Question: Non-Coalescing Droplets

    Reader ancientavian asks:

    I’ve often noticed that, when water splashes (especially as with raindrops or other forms of spray), often it appears that small droplets of water skitter off on top of the larger surface before rejoining the main body. Is this an actual phenomenon, or an optical illusion? What causes it?

    That’s a great observation, and it’s a real-world example of some of the physics we’ve talked about before. When a drop hits a pool, it rebounds in a little pillar called a Worthington jet and often ejects a smaller droplet. This droplet, thanks to its lower inertia, can bounce off the surface. If we slow things way down and look closely at that drop, we’ll see that it can even sit briefly on the surface before all the air beneath it drains away and it coalesces with the pool below. But that kind of coalescence cascade typically happens in microseconds, far too fast for the human eye.

    But it is possible outside the lab to find instances where this effect lasts long enough for the eye to catch. Take a look at this video. Here Destin of Smarter Every Day captures some great footage of water droplets skittering across a pool. They last long enough to be visible to the naked eye. What’s happening here is the same as the situation we described before, except that the water surface is essentially vibrating! The impacts of all the multitude of droplets create ripples that undulate the water’s surface continuously. As a result, air gets injected beneath the droplets and they skate along above the surface for longer than they would if the water were still. (Video credit: SuperSloMoVideos)

  • Liquid Sculptures

    Liquid Sculptures

    Water droplet art celebrates the infinite forms created from the impact of drops with a pool and rebounding jets. It’s a still life captured from split second interactions between inertia, momentum, and surface tension. These examples from photographer Markus Reugels are among some of the most complex shapes I’ve seen captured. Be sure to check out his website for more beautiful examples of liquids frozen in time. (Photo credits: Markus Reugels; via Photigy)

  • Liquid Sculptures

    Liquid Sculptures

    Artist Corrie White uses dyes and droplets to capture fantastical liquid sculptures at high-speed. The mushroom-like upper half of this photo is formed when the rebounding jet from one droplet’s impact on the water is hit by a well-timed second droplet, creating the splash’s umbrella. In the lower half of the picture, we see the remains of previous droplets, mixing and diffusing into the water via the Rayleigh-Taylor instability caused by their slight difference in density relative to the water. There’s also a hint of a vortex ring, likely from the droplet that caused the rebounding jet. (Photo credit: Corrie White)

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    Surface Explosions

    Underwater explosions often behave non-intuitively. Here researchers explore the effects of surface explosions by setting off charges at the air/water interface. Initially, an unconfined explosion’s blast wave expands a cavity radially into the water. This cavity collapses back toward the surface from the bottom up, ultimately resulting in a free jet that rebounds above the water level. Confined explosions behave very differently, expanding down the glass tube containing them in a one-dimensional fashion. The cavity never extends beyond the end of the glass tube, likely due to hydrostatic pressure. (Video credit: Adrien Benusiglio, David Quéré, Christophe Clanet)

  • Bouncing and Break-Up

    Bouncing and Break-Up

    In the collage above, successive frames showing the bouncing and break-up of liquid droplets impacting a solid inclined surface coated with a thin layer of high-viscosity fluid have been superposed. This allows one to see the trajectory and deformation of the original droplet as well as its daughter droplets. The impacts vary by Weber number, a dimensionless parameter used to compare the effects of a droplet’s inertia to its surface tension. A larger Weber number indicates inertial dominance, and the Weber number increases from 1.7 in (a) to 15.3 in (d). In the case of (a), the impact of the droplet is such that the droplet does not merge with the layer of fluid on the surface, so the complete droplet rebounds. In cases (b)-(d), there is partial merger between the initial droplet and the fluid layer. The impact flattens the original droplet into a pancake-like layer, which rebounds in a Worthington jet before ejecting several smaller droplets. For more, see Gilet and Bush 2012. (Photo credit: T. Gilet and J. W. M. Bush)