Ever wanted to try your hand at making these cool billowing ink photos? Photographer Jason Parnell-Brookes has a detailed tutorial over at PetaPixel laying out the necessary tools and set-up. I haven’t tried this out myself, but I hope to! How about you? (Image credit: J. Parnell-Brookes; submitted by clogwog)
Tag: fluid dynamics
Snowflake Still-Life
To take these high-resolution images of individual snowflakes, Nathan Myhrvold and his collaborators built a special camera. Their apparatus keeps the snowflakes chilled despite the strong illumination cast on them. It uses a 500 microsecond shutter and focus-stacking to produce incredibly detailed portraits of these ephemeral subjects. Each snowflake’s shape is the result of the temperature and humidity that crystal experienced as it grew. Since these are natural snowflakes, no two are alike, but, with enough environmental control, it is possible to make twin snowflakes. (Image credit: N. Myhrvold; via Colossal)
Solving the Teapot Effect
The teapot effect — that tendency for liquid to dribble down the outside of the spout when pouring — is a frustration to many tea drinkers. Unraveling the fluid dynamics of this phenomenon has taken various researchers decades, but a team now believe they’ve captured the problem fully. Their full mathematical description is quite dense, but it boils down to a subtle interplay of capillary, viscous, and inertial forces.
Essentially, they found that droplets will always form just under the lip of the spout, thereby keeping that area wetted. The flow rate of the pour (along with the geometry and surface characteristics of the spout) determines how large those droplets can grow. At low flow rates, the droplets can grow large enough to redirect the entire stream around the spout’s edge, creating a hugely frustrating mess. You can see this flow rate effect in the high-speed video below. (Image credit: S. Ferrari; video and research credit: B. Scheichl et al.; via Ars Technica; submitted by Kam-Yung Soh)
A Colorful Fire Tornado
This one definitely belongs in the do-not-try-this-yourself category, but this Slow Mo Guys video of a colorful fire tornado is pretty spectacular. Using an array of different fuels and a ring of box fans, Gav sets up a vortex of flame that transitions smoothly from red all the way to blue. As he points out in the video, the translucency of the vortex is so good that you can see how the two sides of the vortex rotate! (Video credit: The Slow Mo Guys)
Wet Masks Block Droplets Better
As wearing face masks for long periods has become more typical, you may have wondered whether a soggy mask offers less protection. All masks — cloth, surgical, and N-95s — get moist from their wearer’s breath. A recent study indicates this isn’t a cause for alarm, though.
Researchers looked at how relatively high-speed droplets (like those from a cough or sneeze) impact dry and wet masks. These high-speed droplets can break into smaller droplets upon impact with a mask layer. The more layers a mask has, the fewer droplets make it through. But even for single-layer masks*, a moistened mask layer lets fewer droplets through. So you don’t have to worry if it’s a little humid in there. Your mask is still working! (Image credit: top – V. Davidova, other – S. Bagchi et al.; research credit: S. Bagchi et al.; via APS Physics)
* To be clear, you should be wearing masks that are more than a single layer thick. Personally, I’m still only going into indoor public spaces in an N-95 at this point.
Droplet penetration through a mask. Top row: dry, single layer mask. Middle row: wet, single layer mask. Bottom row: wet, triple layer mask. When wet, masks permit fewer droplets through. Breaking Compound Ligaments
When pulled, viscous liquids stretch into ligaments that thin and then break into droplets. In this video, researchers investigate how these ligaments break up, depending on their composition. The initial views show the break-up of a water-glycerol ligament (Image 1) and an oil ligament (Image 2). By placing a water droplet inside oil, the researchers got quite different results, including oil-encapsulated droplets (Image 3). The technique could be useful for making compound droplets, even with more than two components. (Image and video credit: V. Thiévenaz and A. Sauret)
“In Flight”
Photographer Mark Harvey captured these stunning portraits of birds in flight. From acrobatic songbirds to soaring raptors, the images show the incredible morphology of a bird’s wing during flight. Most birds are constantly changing their wing shape to generate lift, change trajectory, and stabilize their flight. Note the separation between the flight feathers in all of these birds. Those gaps are thought help break up the birds’ wingtip vortices, thereby reducing their induced drag. You may also notice that the owls in Harvey’s photos have feathers that look a bit different from the other birds; owls have adaptations in their feathers that help damp out turbulence, which makes them quieter in flight. Prints of Harvey’s images are available on his website. (Image credit: M. Harvey; via Colossal 1, 2)
Triple Leidenfrost Effect
Droplets can skitter across a hot surface on a layer of their own vapor, thanks to the Leidenfrost effect. If two Leidenfrost droplets of the same liquid collide, they merge immediately. But that doesn’t always happen with two dissimilar liquids. A new study looks at how dissimilar Leidenfrost droplets collide. The researchers found that these drops can bounce off one another repeatedly before their eventual merger (Image 1).
Just as a vapor layer prevents the drops from touching the hot plate, a vapor layer forms between them when they collide, preventing contact (Image 2). Because of these three distinct areas of Leidenfrost vapor (one beneath each drop and one between the drops), the researchers call this the triple Leidenfrost effect.
Eventually, the more volatile (in other words, easily evaporated) drop shrinks to a size similar to its capillary length, at which point the drops merge. If the boiling points of the two liquids are vastly different, the merger can be explosive (Image 3). (Image and research credit: F. Pacheco-Vázquez et al.; via APS Physics)
Insects Taking Flight
As awkward as they look sometimes, insects are amazing fliers. In this video from Ant Lab, we see all kinds of insects taking flight. Some, like the mantis, execute flying leaps to get in the air, whereas weevils begin flapping from a tripod stance. Watching these videos I’m always struck by how flexible insect wings are. They flex far more than I would imagine. And these insects have a lot of excess lift. Just check out that carrion beetle taking off despite being covered in mites! (Image and video credit: Ant Lab)
Jovian Circulation
Jupiter‘s atmosphere remains quite mysterious, due to our limited ability to measure the depths of the gas giant’s clouds. But measurements from the Juno spacecraft are continuing to shape researchers’ understanding of our massive neighbor. By tracking ammonia distributions in Jupiter’s belts and zones, a team has found a series of circulation cells similar to the Ferrel cells of Earth’s midlatitudes.
Unlike the stronger Hadley cells and polar cells, Earth’s Ferrel cells are relatively weak. They’re driven by turbulence and the motion of the circulation cells to the north and south. The Northern and Southern hemispheres each have one Ferrel cell. In contrast, Jupiter — with its larger size and higher rotation rate — boasts eight Ferrel-like cells in each hemisphere! (Image and research credit: K. Duer et al.; via Universe Today; submitted by Kam-Yung Soh)
