FYFD

Tag: fluid dynamics

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    Self-Stopping Leaks

    A leak can actually stop itself, as shown in this video. To demonstrate, the team used a tube pierced with a small hole. When filled, water initially shoots out the hole in a jet. The pressure driving the jet comes from the weight of the fluid sitting above the hole. As the water level drops, the pressure drops, causing the jet to sag and eventually form a rivulet that wets the side of the tube. As the water level and driving pressure continue to fall, the rivulet breaks up into discrete droplets, whose exact behavior depends on how hydrophobic the tube is. Eventually, a final droplet forms a cap over the hole and the leak stops. At this point, the flow’s driving pressure is smaller than the pressure formed by the curvature of the capping droplet. (Image and video credit: C. Tally et al.)

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    “Volcano Pilot”

    Today’s video is something a little different. Rather than looking at fluids and their physics directly, we’ll take a step back and think about how people relate to the subject. This short film, “Volcano Pilot,” follows Haraldur Unason Diego as he reflects on his life’s work. It’s a beautiful and moving glimpse of the life and philosophy of a small aircraft pilot. Many people never have the opportunity to see the world from cockpit of a Cessna or similar small aircraft, and I think there are few experiences that can better connect someone to the fluids-in-action that is aviation. (Image and video credit: M. Aberra et al.)

  • Dripping Impact

    Dripping Impact

    How does water drip, drip, dripping onto stones erode a crater? Water is so much more deformable that it seems impossible for it to wear harder materials away, even over thousands of impacts. To investigate this, a team of researchers developed a new measurement technique: high-speed stress microscopy. In the process, they found that water owes its incredible erosive power to three factors: 1) The drop’s impact creates surface shock waves along the material, which helps increase erosive power; 2) After the shock wave passes, a decompression wave in the material helps loosen surface matter; and 3) The spreading drop sends a non-uniform wave of stress across the material that simultaneously presses and scrubs at the surface. Together, these factors enable simple, repetitive droplet impacts to wear away at hard surfaces. (Image credit: cottonbro; research credit: T. Sun et al.; via Cosmos; submitted by Kam-Yung Soh)

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    Inside Viscous Fingers

    Sandwich a viscous fluid between two transparent plates and then inject a second, less viscous fluid. This is the classic set-up for the Saffman-Taylor instability, a well-studied flow in which the interface between the two fluids forms a wavy edge that develops into fingers. Despite its long history, though, there is still more to learn, as shown in this video. Here, researchers alternately injected a dyed and undyed version of the less viscous fluid. The result (Image 3) is a set of concentric dye rings that show how the fluid moves far from the fingers along the edge. Notice that the waviness of the fingers appears in the flowing fluid well before it approaches the interface. (Image and video credit: S. Gowan et al.)

  • Coalescence Symmetry

    Coalescence Symmetry

    When droplets coalesce, they perform a wiggly dance, gyrating as the capillary waves on their surface interfere. When the droplets have matching surface tensions, like the two water droplets in the animation on the lower left, the coalescence dance is symmetric. But for differing droplets, like the water and ethanol droplets merging on the lower right, coalescence is decidedly asymmetric.

    Two water droplets merge symmetrically.
    A water droplet and an ethanol droplet merge asymmetrically.

    The asymmetry arises from the droplets’ different surface tensions. The size and speed of the capillary waves that form on a droplet depend on surface tension, so droplets of different liquids have inherently different capillary waves. During merger, the interference of these capillary waves causes the asymmetry we see. (Image credit: top – enfantnocta, coalescence – M. Hack et al.; research credit: M. Hack et al.)

  • Blowing Up Euler

    Blowing Up Euler

    The mathematics of fluid dynamics still have many unknowns, which makes them an attractive playground for mathematicians of all stripes. One perennial area of interest is the Euler equations, which describe an ideal (i.e., zero viscosity), incompressible fluid. Mathematicians suspect that these equations may produce impossible answers — vortices with infinite velocities, for example — under just the right circumstances, but so far no one has been able to prove the existence of such singularities.

    A recent Quanta article delves into this issue and the race between researchers using traditional methods and those using new deep learning techniques. Will the singularities be found and who will get there first? It’s well worth a read, whether theoretical mathematics is your thing or not. (Image credit: S. Wilkinson; see also Quanta; submitted by Jo V.)

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    Martian Flyover

    Fly over a Martian crater in this incredibly detailed 8K video built from Mars Reconnaissance Orbiter imagery. Like Earth’s deserts, Mars is largely shaped by wind, and we get some fantastic views of sand ripples in this flyover. For reference, the vertical scale covered in the video image is roughly 1 kilometer. It’s pretty astounding to see this kind of detail from a spacecraft 250 kilometers away! (Video and image credit: S. Doran/NASA; via Colossal)

  • Featherwings in Flight

    Featherwings in Flight

    The featherwing beetle is tiny, less than half a millimeter in length. At that scale, flying is a challenge, with air’s viscosity dominating the forces the insect must overcome. The featherwing beetle, as its name suggests, has feather-like wings rather than the membranes larger beetles use. But a new study shows that these odd wings work surprisingly well.

    The beetle’s bristled wings flap with an exaggerated figure-8 motion, with the wings clapping together in front of and behind the insect. The beetle expends less energy moving its feathery wings than it would if they were solid, and it moves its wing covers at the same time to counter each stroke and keep its body steady. (Image and research credit: S. Farisenkov et al.; video credit: Nature; submitted by Kam-Yung Soh)

  • Turquoise Eddies

    Turquoise Eddies

    During the summer months, the Barents Sea between Norway and Russia is streaked with blue and teal swirls. These beautiful patterns are the result of a phytoplankton bloom, as viewed by earth-observing satellites (with a little color enhancement). Although each cell in the bloom is only nanometers across, their collective presence is visible from space! They also act as tracers in the water, revealing the swirling flow patterns present there. (Image credit: J. Stevens/NASA Earth Observatory)

  • Raindrops on the Windshield

    Raindrops on the Windshield

    When I was a child, I was fascinated by the raindrops that shimmied along the windshield of our car. Some would slide up the glass. Some would run down. And some just seemed to wiggle in place, until the car’s speed changed. As common as this sight is, the physics of these droplets is quite complicated and not completely understood.

    Each droplet has a host of forces on it: gravity flattening it or pulling it down an incline; a drag force from the wind flowing over it; and friction between the drop and the surface trying to pin it in place. Recently, scientists have developed a new mathematical model that captures some of the behaviors behind these drops. The work describes the wind speed necessary to move a drop of a given size sitting on a flat surface. The authors also explored how that critical wind speed changes when a drop sits on a tilted surface aligned or against the wind. (Image credit: P. Gupta; research credit: A. Hooshanginejad and S. Lee; via Science News; submitted by Kam-Yung Soh)