FYFD

Tag: 2022gofm

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    Dancing Over Ridges

    When flowing over a ridged surface, particles follow a drifting, helical trajectory. In this video, researchers delve into the physics behind this phenomenon. Differences in the pressure gradient along different parts of the corrugation push particles along the groove. With their analysis, the team is able to predict particle trajectories above surface roughness of any shape. With these tools, they can design roughened microchannels that disperse particles at a desired speed, something that could be especially helpful in medical diagnostics. (Image and video credit: D. Chase et al.; research credit: D. Chase et al.)

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    Turbulence From Vortex Rings

    When vortex rings collide, they reconnect into smaller, rings that eventually break down into chaos. Here, researchers experiment with colliding multiple vortex rings — focusing on an eight-ring collision. When they collide rings over and over, it creates a zone of isolated turbulence at the heart of the collisions.

    Many of the theories and predictions that exist around turbulence assume that the flow is homogeneous and isotropic; what this means is that the (statistical) characteristics of the flow are the same in every direction. In reality, this kind of flow isn’t always easily achieved, which makes testing theoretical predictions challenging.

    What’s neat about this set-up is that you get this desired turbulence in a very controlled way. It’s easy to tune the size and energy of your vortex rings, and those tweaks allow you to observe what — if any — changes occur in the resulting turbulence. (Image and video credit: T. Matsuzawa et al.)

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    Little Surfer

    Here’s another look at SurferBot, a low-cost, vibration-based robot capable of traversing both water and land. SurferBot’s vibration creates asymmetric ripples on the water surface. Because the waves are bigger at the rear of the robot, it gets propelled forward. But there doesn’t have to be water for SurferBot to get around! It’s actually amphibious, moving on both land and water. It can even transition from land to water on its own. (Image and video credit: E. Rhee et al.; research credit: E. Rhee et al.)

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    Snowing in the Core

    Some rocky planetary bodies, like Jupiter‘s moon Ganymede, generate magnetic fields through snow-like, solid precipitation that falls in their liquid metal cores. To study this peculiar and complex arrangement, researchers look at sugar grains falling through — and dissolving into — water. The solid sugar grains mimic the iron snowflakes that fall in Ganymede’s core. As they sink, they drag fluid with them. But the grains can also dissolve, making the fluid around them denser and prone to sinking even faster. The dense, sinking flows trigger buoyant convection inside the surrounding fluid.

    As seen in the experiments, there are many factors competing here. Large grains dissolve more slowly and are able to drag more fluid with them as they fall. Small grains, on the other hand, dissolve quickly, causing more buoyancy-driven flows. Laboratory analogs like these help scientists unravel the complexities of situations we cannot observe otherwise. (Image and video credit: Q. Kriaa et al.)

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    Self-Propelled Droplets

    Drops of ethanol on a heated surface contract and self-propel as they evaporate. My first thought upon seeing this was of Leidenfrost drops, but the surface is not nearly hot enough for that effect. Instead, it’s significantly below ethanol’s boiling point. Looking at the drops in infrared reveals beautiful, shifting patterns of convection cells on the drop. The patterns are driven by the temperature difference along the drop; at the bottom, the drop is warmest, and at its apex, it is coldest. Those differences in temperature create differences in surface tension, which drives a surface flow that breaks the drop’s symmetry. The asymmetry, the authors suggest, is responsible for the drop’s propulsion. (Image and video credit: N. Kim et al.)

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    Simulating Schools

    In nature, fish school for many reasons: protection from predators, increased sensing, and hydrodynamic advantages. To capture this complex behavior, researchers are building their own digital fish, governed by known rules. Here, scientists give each fish social rules — based on vision range and preferred distance from a neighbor — and hydrodynamic rules — based on a fish’s wake. With the rules in place, they can then observe the schooling behaviors of their digital fish. Like their real counterparts, these schools show different flocking based on apparent “moods”. (Image and video credit: J. Zhou et al.)

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    Draining a Bottle

    Turn a bottle upside-down to empty it, and you’ll hear a loud glug-glug-glug as the liquid in the bottle empties and air rushes in. In this video, researchers aim a high-speed camera at the very first bubble that forms during the process. Once the bubble reaches the wider area of the bottle, it tends to pinch off in the bottle’s neck. That creates a narrow jet that pierces the bubble and flies all the way to the other side, leaving a column of liquid inside the rising bubble. Increasing the fluid’s viscosity has remarkably little effect, at least until the liquid is extremely viscous. (Image and video credit: H. Mayer et al.)

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    Classifying Waves

    In a lab, researchers create their waves in a long, clear-sided tank, where they can observe how the waves form, travel, and interact. To generate the wave, they use a plate, attached to a piston. Push the water at one end, and a wave forms. The type of wave that forms depends on both the velocity and the stroke length of the piston, as shown in this video. By mapping out these two variables, researchers can observe all different sorts of waves, from peaceful solitary waves to wild, plunging breakers. (Image and video credit: W. Sarlin et al.)

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    In a Box, Shaken

    Tidal areas experience lots of oscillating, back-and-forth flow that builds up patterns in the sand below. In this experiment, researchers investigate a similar situation by filling a box with water and spherical particles, then shaking the box from side-to-side. Inside the box, the particles line up in chains that are perpendicular to the direction of oscillation (think sand ripples parallel to a shoreline). In this simplified system, the team can then look at what forces align the particles, how defects in the pattern shift, and what happens when the oscillation gets bigger. (Image and video credit: T. van Overveld et al.)

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    Walking in the Wake

    Flow visualization is an important tool in fluid dynamics, and scientists have many ways to capture and visualize flow information. But our methods are not the only — or even the best — ways to express a flow. Here, engineers teamed up with architects and artists to explore the flow behind an oscillating cylinder. When free to move forward-and-backward the cylinder’s wake takes on three distinctively forms. The team explored many ways to display the wakes — drawings, 3D-printed sculptures, and more — before ultimately building an art installation that lets visitors walk through the wake to experience it. I love the creativity of these interdisciplinary efforts. To see a similar, yet very different, take on the wake of a cylinder, check out this interpretative dance. (Image and video credit: P. Boersma et al.)