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Search results for: “lift”

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    Long-Lived Bubbles

    Without surfactants to stabilize them, bubbles don’t last long at room temperature. But adding a little heat changes the picture. When heated, the bubbles get stabilized by a thermal gradient that lifts fluid toward the bubble’s peak, where it cools and gathers. Eventually, the cold fluid grows heavy enough to sink down the side of the bubble (in either a constant stream or occasional drips); with warm fluid getting pulled up to replace it (via the Marangoni effect), the process repeats and the bubble lives on. (Video credit: S. Nath et al.; see also)

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    Bouncing Bullets Off Water

    With the right shot, it’s possible to skip a bullet off water, as shown in this video from the Slow Mo Guys. The angle of the bullet relative to the water needs to be quite shallow, as this sets the bullet up for the hydrodynamic lift needed to skip. Physically, the mechanism for skipping a bullet is similar to rock-skipping. The bullet’s impact creates a cavity that the bullet rides. With the right conditions, the cavity orients the bullet upward, creating the lift needed to skip. (Video and image credit: The Slow Mo Guys)

  • Cellular Clouds

    Cellular Clouds

    Though tough to make out from the surface, our oceans are often covered by cell-shaped clouds stretching thousands of kilometers. This satellite image shows off two such types of marine stratocumulus cloud. Open-celled clouds appear as thin wisps of vapor around an empty middle; in these clouds, cool air sinks through the center while warm air rises along the edges. Open-celled clouds are good rain producers.

    On the flip side, closed-cell clouds have a vapor-filled center and breaks in the cloud cover along each cell’s edge. These clouds don’t produce much rain, but they do lift warm, moist air through their middles and let cool air sink along their edges. Closed-cell clouds tend to last much longer than their open-celled counterparts; they can stick around for half a day, whereas open-celled clouds break up in only a couple hours. (Image credit: J. Stevens; via NASA Earth Observatory)

  • Why Moths Are Slow Fliers

    Why Moths Are Slow Fliers

    Hawkmoths and other insects are slow fliers compared to birds, even ones that can hover. To understand why these insects top out at 5 m/s, researchers simulated their flight from hovering to forward flight at 4 m/s. They analyzed real hawkmoths flying in wind tunnels to build their simulated insects, then studied their digital moths with computational fluid dynamics.

    During hovering flight, they found that hawkmoths generate equal amounts of lift with their upstroke and downstroke. As the moth transitions into forward flight, though, its wing orientation shifts to reduce drag, and the upstroke stops being so helpful. Instead, the upstroke generates a downward lift that the downstroke has to counter in addition to the insect’s weight. At higher forward speeds, this trend gets even worse.

    The final verdict? Hawkmoths don’t have the flexibility to twist their wings on the upstroke the way birds do to avoid that large downward lift. Since they can’t mitigate that negative lift, the insects have a slower top speed overall. (Image and research credit: S. Lionetti et al.; via APS Physics; submitted by Kam-Yung Soh)

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    Moths and Beetles in Flight

    Watching insects take flight in high-speed video is always mesmerizing. So often their wings look too small and fragile to lift their bulbous bodies, but they manage the feat easily. I especially like to watch how much their wings flex during each up- and downstroke. So often we think that stiffer wings — like those on airplanes — are better for flight, yet nature demonstrates at so many sizes that flexibility is better, especially in flapping flight. A flexible wing can maximize lift in the downstroke and curl to minimize drag on the upstroke. Even wings that fold away, as many beetle wings do, can do the job of lifting an insect once shaken out. (Image and video credit: Ant Lab)

  • Bird Photographer of the Year 2022

    Bird Photographer of the Year 2022

    Try as we might, humans cannot understand fluid dynamics as birds do. Whether they are primarily flyers or swimmers, birds have an innate understanding of lift and other aerodynamic forces that put the best engineers to shame. Shown here are a subset of winners from the 2022 Bird Photographer of the Year competition, each of them showing off fluid dynamics in some fashion. Hummingbirds hover, droplets shine like diamonds, and divers brace for impact. You can peruse more winner at BPOTY’s website. (Image credits: Various; see alt text of individual images)

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    Groundwater-Structure Interactions

    Groundwater can sometimes wind up in unexpected places, given the way it interacts with subsurface structures. In this Practical Engineering video, Grady discusses the paths that groundwater takes around structures and how civil engineers account for groundwater-related forces on dams and other buildings. As always, he illustrates with excellent model demos, allowing viewers to see groundwater interactions for themselves. (Image and video credit: Practical Engineering)

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    Pumping Waste

    Sewage systems rely on gravity to remove waste from our homes and carry it toward treatment plants. But that constant downward slope can’t always be maintained. Sometimes we have to bring the sewage back up to the surface to process it. For that, modern systems rely on pumps and other equipment to move the challenging slurry of liquid and solid materials. In this video, Grady from Practical Engineering breaks down the physics and engineering of sewage pumping. (Image and video credit: Practical Engineering)

  • Perching Aerodynamics

    Perching Aerodynamics

    When birds come in for a landing, they pitch back and heave their wings as they come to a stop in a perching maneuver. Some birds, researchers noticed, partially fold their wings during the move, creating what’s known as a swept wing. Curious as to the effect of this sweep, the team recreated the wing motion of a perching bird using two flat plates — one rectangular and one swept — and measured the flow around them during the maneuver. They found that the swept wing had greater lift, thanks to a spanwise flow inherent to swept wings that helped stabilize the leading-edge vortex. (Image credit: D. George; research credit: D. Adhikari et al.; via APS Physics)

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    Morphing Particle Rafts

    A layer of tiny glass beads sitting atop a pool of castor oil becomes a morphing surface in this video. Applying an electric field creates enough electrostatic force to draw the interface upward against the power of both gravity and surface tension. Moving the electric field — either by shifting the electrode or simply moving a finger over the surface — is enough to pull columns of fluid along! I could imagine this making some very cool human-machine interfaces one day. (Image and video credit: K. Sun et al.)

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