FYFD

Tag: flow visualization

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    The Coexistence of Order and Chaos

    One of the great challenges in fluid dynamics is understanding how order gives way to chaos. Initially smooth and laminar flows often become disordered and turbulent. This video explores that transition in a new way using sound. Here’s what’s going on.

    The first segment of the video shows a flat surface covered in small particles that can be moved by the flow. Initially, that flow is moving in right to left, then it reverses directions. The main flow continues switching back and forth in direction. This reversal tends to provoke unstable behaviors, like the Tollmien-Schlichting waves called out at 0:53. Typically, these perturbations in the flow start out extremely small and are difficult or even impossible to see by eye. So researchers take photos of the particles you see here and analyze them digitally. In particular, they are looking for subtle patterns in the flow, like a tendency for particles to clump together with a consistent spacing, or wavelength, between them. Normally, researchers would study these patterns using graphs known as spectra, but that’s where this video does something different.

    Instead of representing these subtle patterns graphically, the researchers transformed those spectra into sound. They mapped the visual data to four octaves of C-major, which means that you can now hear the turbulence. When the audio track shifts from a pure note to an unsteady warble, you’re hearing the subtle disturbances in the flow, even when they’re too small for your eye to pick out.

    The last part of the video takes this technique and applies it to another flow. We again see a flat plate, but now it has a roughness element, like a tiny hockey puck, stuck to it. As the flow starts, we see and hear vortices form behind the roughness. Then a horseshoe-shaped vortex forms upstream of it. Aside from the area right around the roughness, this flow is still laminar. But then turbulence spreads from upstream, its fingers stretching left until it envelops the roughness element and its wake, making the music waver. (Video and image credit: P. Branson et al.)

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    Psychedelic Faraday Waves

    Vibrate a pool of water and above a critical frequency, a pattern of standing waves will form on the surface. These are known as Faraday waves after Michael Faraday, who studied the phenomenon in the early half of the nineteenth century. The kaleidoscopic view of them you see here comes from photographer Linden Gledhill, who used a high-speed camera and an LED ring light reflecting off the water to capture the changing motions of the waves. The wave patterns oscillate at half the frequency of the driving vibration, and, as the driving frequency changes, the wave patterns shift dramatically. Higher frequencies create more complicated patterns. (Image and video credit: L. Gledhill)

  • Dissolving Candy

    Dissolving Candy

    In nature, solid surfaces often evolve over time in conjunction with the flows around them. This is how stalactites, canyons, and hoodoos all form and change over time. Here researchers examine a surface formed from hard candy that is dissolving from below. Over time, the initially flat surface develops a pitted appearance (top image, scale bar is 1 cm) with roughness that is approximately 1 mm in scale. Flow visualization (bottom row) suggests that these pits result from local flow where narrow, millimeter-sized dense plumes fall away from the surface. 

    As material dissolves from the candy, it forms a dense layer of sugar-water mixture near the solid surface. Once that layer grows to a critical thickness, it will be too unstable for viscosity to counter. At that point, the Rayleigh-Taylor instability takes over, causing the dense sugar-water layer to break up into narrow, sinking plumes. Although each area is evolving independently, the rate at which material dissolves is uniform everywhere, so the dissolving body retains the same shape over time. (Image and research credit: M. Davies Wykes et al., source)

  • Impressionist Foams

    Impressionist Foams

    Imagine taking two panes of glass and setting them in a frame with a small gap between them. Then partially fill the gap with a mixture of dye, glycerol, water, and soap. After turning the frame over several times, the half of the frame will be filled with foamy bubbles. When you flip it again, the dyed glycerol-water will sink and penetrate the bubble layer, creating complex and beautiful patterns as it mixes. Some of the bubbles may get squeezed together until they coalesce into larger bubbles that shoot upward thanks to their increased buoyancy. Other smaller bubbles will wend their way upward as neighboring fluid shifts. If you examine the tracks left by individual bubbles, you can find patterns reminiscent of Impressionist paintings, as seen at the end of this Gallery of Fluid Motion video. (Image credit: A. Al Brahim et al., source)

  • Sunset Flow

    Sunset Flow

    Day and night mix in this flow visualization of watercolor pigments and ferrofluid. The former, as suggested by their name, are water-based, whereas ferrofluids typically contain an oil base. This means the two fluids are immiscible. Like oil and vinegar in salad dressing, the only way to mix them is to break one into tiny droplets floating in the other. This is what happens near their boundary, where brightly-colored paint droplets float in a network of dark channels. To the right, the paint and ferrofluid have been swirled around to create viscous mixing patterns among the paint colors with occasional intrusions of thin ferrofluid fingers. (Image credit: G. Elbert)

  • Cloud Chambers

    Cloud Chambers

    Cloud chambers were one of the first methods used to study radioactive decay and cosmic particles. Such chambers are filled with a cool, supersaturated cloud of alcohol vapor. When high-energy particles pass through, they collide with atoms in the chamber, ionizing them. Those ions then serve as nucleation sites for the alcohol vapor, creating a condensation streak that marks the particle’s passage. In some respects, they’re similar to the contrails that form behind airplanes. What you’re seeing is not the particle itself but evidence that it went by. YouTuber Nick Moore built his own cloud chamber. Learn more about it and see lots more great footage of it in action in the full video below. (Image and video credit: N. Moore)

  • Visualizing Acoustic Levitation

    Visualizing Acoustic Levitation

    The schlieren photographic technique is often used to visualize shock waves and other strong but invisible flows. But a sensitive set-up can show much weaker changes in density and pressure. Here, schlieren is used to show the standing sound wave used in ultrasonic levitation. By placing the glass plate at precisely the right distance relative to a speaker, you can reflect the sound wave back on itself in a standing wave, seen here as light and dark bands. The light bands mark the high-pressure nodes, where the pressure generated by the sound waves is large enough to counteract the force of gravity on small styrofoam balls. This allows them to levitate but only in the thin bands seen in the schlieren. Move the plate and the standing wave will be disrupted, causing the bands to fade out and the balls to fall. (Video and image credit: Harvard Natural Sciences Lecture Demonstrations)

  • Space Shuttle Sonic Booms

    Space Shuttle Sonic Booms

    The Space Shuttle had a famous double sonic boom when passing overhead during re-entry. This schlieren flow visualization of a model shuttle at Mach 3 reveals the source of the sound: the fore and aft shock waves on the vehicle. The nose of the shuttle generates the strongest shock wave since it is the first part of the vehicle the flow interacts with. This initial shock wave turns the flow outward and around the shuttle. The second boom comes from the back of the shuttle and serves to turn the flow back in to fill the wake behind the shuttle. (The actual shock wave would look a little different than this one because there’s no sting holding the shuttle like there is with the model.) The other major shock wave comes from the shuttle’s wings, but, at least for this Mach number, the wing shock wave merges with the bow shock, making the two indistinguishable. (Image credit: G. Settles, source)

  • Chemistry in Infrared

    Chemistry in Infrared

    Many chemical reactions, and the flows that accompany them, are invisible to the human eye. But in infrared wavelengths those same events are vibrant and energetic. In this video from the Beauty of Science group, various chemical reactions are shown in visible and IR wavelengths, revealing very different perspectives on the same thing. Many of the reactions are exothermic, meaning that they produce heat as they occur. Because of this the thermal imaging shows where the most intense reaction is occurring at a given time. Other areas gradually darken as diffusion and flow move and dilute the heat energy released. (Video and image credit: Beauty of Science, source)

  • “Moving Creates Vortices and Vortices Create Movement”

    “Moving Creates Vortices and Vortices Create Movement”

    A new interactive installation by the Japanese art collective teamLab uses the movement of visitors to drive vortex motion. Entitled “Moving Creates Vortices and Vortices Create Movement,” the installation uses projectors in a mirror room to create the sensation of an infinite, indoor ocean that’s constantly churned by the paths visitors take. In the absence of motion, the room slowly fades to darkness. The installation is currently in the National Gallery of Victoria in Melbourne, Australia, and will be open until April 15th, 2018. (Image credit: teamLab; via Colossal; submitted by jshoer)

    P.S. – Winter Olympic coverage will start on Monday, February 12th! – Nicole