FYFD

Tag: hydraulic jump

  • The Jumping Jump

    The Jumping Jump

    Turn on your kitchen sink, and the falling jet may form a circle of shallow flow where it strikes the sink. This fast-moving region of flow, surrounded by a wall of water, is a hydraulic jump. A recent study delves into a previously-missed phenomenon of this flow: intermittent disruption and reappearance.

    An oscillating hydraulic jump, viewed from below.
    An oscillating hydraulic jump, viewed from below.

    The team found that, within a narrow range of jet and surface sizes, a hydraulic jump will periodically appear and disappear. The effect comes from the hydraulic jump itself; waves from the jump propagate outward, hit the edge of the circular plate, and reflect inward. When the incoming and outgoing waves interfere, it floods the jump zone, making it disappear briefly. (Image credit: sink – Nik, jump – A. Goerlinger et al.; research credit: A. Goerlinger et al.; via APS Physics)

  • Polygonal Jumps

    Polygonal Jumps

    When you turn on your kitchen faucet, you may have noticed a big circle that forms on the bottom of the sink. This is a hydraulic jump, a region where fast-moving, shallow flow shifts to a slower-moving, deeper flow. Although these jumps start out circular, if the fluid is deeper than a critical value, the jump will break down and form polygons, like the one above. Exactly what shape the jump forms depends on many factors: flow speed, fluid depth, and flow history. The same flow conditions can even form more than one shape. But all of these shapes have one thing in common: their corners are universally around 114 degrees with a radius of 3.5 millimeters. (Image and research credit: S. Tamim et al.; via PRF)

  • Mountains in the Sky

    Mountains in the Sky

    Our skies can sometimes presage the weather to come. In thunderstorms, a cirrus plume above an anvil cloud will often appear (visible by satellite) about half an hour before severe conditions are reported on the ground. A new study delves into the origins of these plumes and finds that they result from an internal hydraulic jump in the storm that acts a bit like an artificial mountain, driving air — and the moisture it contains — higher in the stratosphere than normal. Once the jump is established, the authors found it could drive 7 tonnes per second of water vapor into the stratosphere! (Image credit: jplenio; research credit: M. O’Neill et al.; via Science)

  • Featured Video Play Icon

    Hydraulic Jumps

    Chances are that you’ve seen plenty of hydraulic jumps in your life, whether they were in your kitchen sink, the whitewater of a river, or at the bottom of a spillway. Practical Engineering has a great primer on this oddity of open channel flow. 

    When water (or other liquids) flow with a surface open to the air – think like a river rather than a pipe – the flow has three important regimes: subcritical, critical, and supercritical. Which state the flow is in depends on the speed of the flow compared to the speed of a wave traveling in that flow. If the waves are faster than the flow, we call it subcritical. If the flow is faster than the waves, it’s called supercritical. (This is equivalent to subsonic or supersonic flow, where the regime depends on the flow speed compared to the speed of sound.)

    Flows can transition naturally from one state to another, and where they transition from fast, supercritical flow to slower, subcritical flow, we find hydraulic jumps – places where the kinetic energy of the supercritical flow gets changed into turbulence and potential energy through a change in height. Check out the video above to learn how civil engineers use hydraulic jumps to control water and erosion. (Video and image credit: Practical Engineering)

  • The Driver of Hydraulic Jumps

    The Driver of Hydraulic Jumps

    You’ve seen it a million times. When you turn on your kitchen faucet, the falling water forms a distinctive ring – known as a hydraulic jump – in the bottom of your sink. First described by Leonardo da Vinci, this phenomenon has been studied for centuries, and, for nearly all of that time, scientists assumed that gravity played a major role, even in kitchen-sink-sized hydraulic jumps. But that’s not the case.

    A newly published study shows that gravity can’t be a major player in setting the radius of these small-scale hydraulic jumps because they form the same whether the jet impinges from above, below, or sideways. Instead, the researchers found that surface tension and viscosity are the parameters that determine the jump’s formation. It’s not every day that you get to overturn a centuries-old theory in physics! (Image credit: J. Kilfiger; research credit: R. Bhagat et al.; via Silicon Republic; submitted by Patrick D.)

  • Cloud Flows

    Cloud Flows

    When viewed at the right pace, clouds can flow. This timelapse of fog over Mt. Tamalpais State Park near San Francisco shows clouds moving over the hills there. Physically, this flow is an example of a familiar phenomenon known as a hydraulic jump. It happens when a fast-moving flow moves into a region of slower flow. The kinetic energy of the incoming flow gets transferred into potential energy, causing the flow to suddenly rise in height. It can also trigger turbulence, as seen on the right side of the animation. Watch carefully along a river, and you’ll see the same thing happening. Or, if your kitchen sink has a flat bottom, you can create a circular hydraulic jump just by turning on the faucet. You’ll get a region of fast flow right where the water impacts the basin, and a little ways out, you’ll see a circular jump where the water is suddenly taller and slower. That’s a hydraulic jump, too! (Image credit: Nicholas Steinberg Photography, source; submitted by Madi R.)

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    Living Fluid Dynamics

    This short film for the 2016 Gallery of Fluid Motion features Montana State University students experiencing fluid dynamics in the classroom and in their daily lives. As in her previous film (which we deconstructed), Shanon Reckinger aims to illustrate some of our everyday interactions with fluids. This time identifying individual phenomena is left as an exercise for the viewer, but there are hints hidden in the classroom scenes. How many can you catch? I’ve labeled some of the ones I noticed in the tags. (Video credit: S. Reckinger et al.)

  • Dam Release

    Dam Release

    Here the U.S. Army Corps of Engineers release 13,000 cubic feet per second (~370 cubic meters per second) of water at a dam in Oklahoma. That’s the equivalent of nine-and-a-half shipping containers a second! Releasing that much water at once has created an enormous hydraulic jump, seen on the right side of the animation. Hydraulic jumps are kind of like the shock wave of open channel flow. On the left side of the image, water is moving smoothly and swiftly down the sluiceway. At the center, the incoming water encounters the large, slow-moving mass of water already in the lake. There’s no way for the incoming water to sustain its kinetic energy while discharging into the lake. Instead a hydraulic jump forms, converting the incoming flow’s kinetic energy into potential energy, as seen in the sudden height increase. Some of the energy is also converted to turbulence and dissipated as heat. (Image credit: U.S. Army Corps of Engineers/AP, source; via Gizmodo)

  • 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)

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    Hydraulic Jump in the Lab

    When fast-moving liquids encounter regions of slow-moving liquids, they decelerate rapidly, trading their kinetic energy for potential energy and creating a hydraulic jump. Flow in the video above is from left to right. The depth difference between the incoming and outgoing water can be directly related to the velocity of the incoming fluid. Hydraulic jumps in rivers and spillways are often extremely turbulent, like the one in this video, but laminar examples exist as well. In fact, with the right height and flow rate, you can create stable hydraulic jumps right in your kitchen sink. The hydraulic jumps formed from a falling jet are typically circular, but with the right conditions, all sorts of wild shapes can be observed. (Video credit: H. Chanson)