FYFD

Category: Research

  • Inside Hydroplaning

    Inside Hydroplaning

    When a tire spins over a wet roadway, pressure at the front of the tire generates a lifting force; if that lift exceeds the weight of the car, it will start hydroplaning. To prevent this, the grooves of a tire’s tread are designed to redirect the water. Now researchers have visualized flow inside these grooves for the first time, using a version of particle image velocimetry (PIV). PIV techniques use fluorescent particles to track the flow.

    The results reveal a complicated, two-phase flow inside the tire grooves. As seen in the images above, bubble columns form inside the tire grooves. The team’s results suggest that the bubble columns depended on groove width, spacing, and intersections with other grooves. They also saw evidence of vortices inside some grooves. (Image credit: tires – S. Warid, others – D. Cabut et al.; research credit: D. Cabut et al.; via Physics World; submitted by Kam-Yung Soh)

  • A Macro View of Weathering

    A Macro View of Weathering

    Water constantly weathers sedimentary rock, both physically — through abrasion — and chemically — through dissolution and recrystallization. Now researchers have gotten their first view of this weathering at the Ångstrom level by observing porous rocks with environmental transmission electron microscopy as they interact with both water vapor and liquid water.

    As expected, the experiments with liquid water showed that water dissolved the rocks and substantially changed the geometry of the rock’s pores. But the experiments also showed significant weathering from water vapor alone. The researchers found that water vapor formed a film on the surface of the rock’s pores in a process known as adsorption. This film substantially decreased the size of each pore and created strain in the rock. Once the water vapor was removed, the rock’s pores were notably altered, supporting the idea that this adsorption was, itself, a form of weathering. (Image credit: M. Kosloski; research credit: E. Barsotti et al.; via AGU EOS; submitted by Kam-Yung Soh)

  • Swapping Emulsions

    Swapping Emulsions

    Chemically speaking, oil and water don’t mix. But with a little fluid mechanical effort, it’s possible to make them an emulsion — a mixture of oil droplets in water or water droplets in oil. Researchers in the Netherlands discovered that the viscosity of these emulsions depends critically on which of those mixtures you have.

    To create their emulsions, the team used a tank consisting of two concentric cylinders. When the inner cylinder spins, it creates a well-understood flow field between the inner and outer cylinder. By varying the ratio of oil to water in the tank, they could explore a wide range of emulsions. They found that the emulsion’s viscosity changed dramatically when the emulsion shifted from oil droplets in water to water droplets in oil, something known as a catastrophic phase inversion. During this switch the viscosity dropped from 3 times higher than pure water to 2 times lower! (Image credit: A_Different_Perspective; research credit: D. Bakhuis et al.; via APS Physics; submitted by Kam-Yung Soh)

  • Decelerating Jets

    Decelerating Jets

    For more than a century, scientists have been fascinated by the jet that forms after a drop impacts a liquid. In this study, researchers tracked fluorescent particles in the fluid to understand the velocity and acceleration of flow inside the jet. They found that, within the first 10ms after the jet appears, it decelerates at up to 20 times the gravitational acceleration. That’s much too fast for gravity to cause, pointing instead to the critical importance of surface tension in dictating the behavior of these fast-moving jets. (Image and research credit: C. van Rijn et al.; via APS Physics; submitted by Kam-Yung Soh)

  • Whiskey Webs

    Whiskey Webs

    Unlike scotch whisky, when American bourbon whiskeys are diluted, they form unique web-like evaporation patterns. These differences arise in part from the way the liquors are aged: scotch is aged in re-used barrels, whereas bourbons require aging in a new, charred American white oak barrel*.

    During aging, the whiskey picks up water-insoluble chemicals from the barrel. When water is added to the bourbon, it helps transport those insoluble components to the surface of a droplet, where they form a monolayer of fatty acid chains (Image 2; in green). As evaporation continues and the droplet gets smaller, the molecules at the shrinking surface collapse inward, forming the rigid web structure we see left behind. The patterns that form act as a kind of fingerprint for the bourbon. Check out some of the brand-to-brand variations over at the researchers’ Whiskey Webs site. (Image and research credit: S. Williams et al.; via Physics Today)

    * In case you were wondering, this is actually a legal requirement in order to be considered bourbon. Bourbons must also be made from a grain mixture that is >50% corn.

  • Featured Video Play Icon

    Insect-Inspired Flight

    Insects are incredibly agile and resilient fliers, capable of colliding and recovering without damage. Engineers are only beginning to capture these characteristics in their robots. Here, engineers use a soft actuator — a rubber cylinder coated in carbon nanotubes — to drive their robot’s flight. When voltage is applied across the carbon nanotubes, the rubber squeezes and stretches, causing the robot’s wings to flap. These soft actuators are far less fragile than hard ones, allowing the robots to take hits and keep flapping, much like the real insects. (Image and video credit: MIT News; research credit: K. Chen et al.)

  • Meltwater Tracking Via Seal

    Meltwater Tracking Via Seal

    Monitoring meltwater from Antarctic glaciers is critical for understanding our changing climate, but such remote and inaccessible regions are tough to collect data in. So researchers are turning to local workers to help them gather data. By collecting and analyzing data from seal tags, researchers have mapped new seasonal variations in meltwater flows around Pine Island Glacier. Although the seals are somewhat tough collaborators — they rarely swim exactly where the researchers would like them to — their winter activities are revealing data researchers could never have collected on their own. (Image credit: Y. Rzhemovskiy; research credit: Y. Zheng et al.; via Gizmodo)

  • Jumping Frost

    Jumping Frost

    Liquid water is easily electrically charged, due to its polar nature. That’s why rubbing a comb is enough to deflect a stream of water. Ice is harder to charge, but it can happen, especially when there are temperature gradients across the ice.

    That’s the key behind this study of jumping frost. When ice crystals grow on a surface much colder than their surroundings, positive charges gather in the colder region, leaving the dendritic branches of the ice negatively charged. When researchers brought liquid water near the charged ice crystals, the water became charged, too. Positive charges in the water attracted the negatively-charged dendrites, causing the ice crystals to jump off the surface.

    Studies like this help us better understand cloud and rain formation and may one day lead to new ways of de-icing surfaces. (Image credit: frost – Miriams-Fotos, figure – R. Mukherjee et al.; research credit: R. Mukherjee et al.; via ChemBites; submitted by Kam-Yung Soh)

    Figure showing snapshots of dendritic ice as it jumps off a surface due to electrostatic charge.
  • Freezing Splats

    Freezing Splats

    In fluid physics, there’s often a tug of war between different effects. For droplets falling onto a surface colder than their freezing point, the hydrodynamics of impact, sudden heat transfer, and solidification processes all compete to determine how quickly and in what form droplets freeze.

    The images above form a series based on changing the height from which the droplet falls. Each image is divided into two synchronized parts. On the left, we see a visible light, top-down view of the freezing droplet; on the right, we see an infrared view of freezing. As the height of impact increases, the shape of the frozen drop becomes more elaborate, moving from a flat splat with a small conical tip all the way to one with a concentric double-ring in its center. (Image and research credit: M. Hu et al.)

  • Chaotic Mixing in Porous Media

    Chaotic Mixing in Porous Media

    One of the peculiar characteristics of viscous, laminar flows is that they are reversible. Squirt dye into glycerin, stir it one way, then the opposite direction, and the dye returns to its initial position. But this neat trick only works in simple geometries; in a more complex environment, like the pores between packed gravel, flows cannot make their way back to their initial state.

    That’s the idea at the heart of this new study of mixing in porous media. Researchers took a bed of packed beads and pushed a slow, steady flow of dye into the bed. Then they steadily withdrew fluid to reverse the flow and observed how the dye they’d injected appeared at the surface of the bed (top image). If the flow were perfectly reversible, we’d expect the dye to return to its injection point. But instead the dye is spread chaotically across the surface, giving researchers a snapshot of the chaotic mixing taking place between beads. (Image and research credit: J. Heyman et al.; via APS Physics)