Here’s a fun activity you can do while you #StayHome: build a self-starting siphon. Michael from VSauce explains how in this video. Moving fluids from one location to another is almost always about pressure, and a siphon is no different. To get the water to flow, there must be unequal pressures driving the liquid to move from high pressure to lower pressure. This is the basic physics behind any siphon; the fun of a self-starting siphon comes from generating enough pressure imbalance to start flow without applying suction. (Video credit: D!NG/M. Stevens)
Inspired by protecting people and property from lava flows, researchers investigated how viscous fluids flow downhill past large obstacles. As seen above, when the obstacle is tall enough that the flow does not overtop it, there’s substantial deflection of the fluid both up- and downstream. Upstream of the barrier, the flow gets deeper, and downstream there’s a dry region left behind.
The researchers modeled these flows numerically, leading to equations designers can use to predict the necessary height, strength, and shape of barrier necessary to protect areas from encroaching lava. (Image and research credit: E. Hinton et al.)
Few sights look as apocalyptic as the leading edge of an incoming dust storm. Known as a haboob, these storms form when a downdraft spreads along the ground, picking up loose dust as the storm front advances. Winds inside the haboob can be severe; when one swept through Denver last year, my first clue was the trees outside my window whipping back and forth wildly, followed by the sky going dark and brownish. Photographer Mike Olbinksi’s short film offers a far better vantage, letting viewers appreciate the towering cloud as it bears down. (Video and image credit: M. Olbinski)
Australia’s bushfires from earlier this year are offering new insights into how pyrocumulonimbus clouds can affect our stratosphere. A massive, uncontrolled blaze between December 29th and January 4th generated a towering, turbulent cloud of smoke like the one shown above.
Using meteorological data, a new study shows this enormous cloud initially rose to 16 km in altitude, then began a months-long trek that circled the globe. The smoke plume ultimately stretched to over 1,000 km wide and reached a record altitude of over 31 km. Inside the plume, concentrations of water vapor and carbon monoxide were several hundred percent higher than normal stratospheric air.
Researchers found the plume extremely slow to dissipate, possibly due to strong rotational winds surrounding it. This is the first time scientists have observed these shielding winds, and work is still underway to determine how and why they formed. (Image credit: M. Macleod/Wikimedia Commons; research credit: G. Kablick III et al.; via Science News; submitted by Kam-Yung Soh)
Hummingbirds are impressive, acrobatic flyers. Their figure-8 wing stroke pattern produces about 70% of their lift on the downstroke, and the remainder during the backward upstroke. But their tails and body motions also play an important role in stabilizing them, especially in gusty winds. They also have some impressive feeding dynamics. Altogether, they’re one of the most precise flyers in the animal kingdom! (Video and image credit: BBC Earth)
A glacier’s snowline marks the location where the amount of summer melting and accumulated snowmass are equal. If, over the course of a season, a glacier experiences more snowfall than melting, its snowline will advance. If melting outweighs accumulation, then the snowline will retreat to higher altitudes. Tracking the snowline gives scientists important data about how the glacier is changing.
And that change is typically slow. When glaciers stop advancing, their snowlines can remain unmoving for decades. Or, at least, they used to. In recent years, Alaska’s Taku Glacier was one of the only alpine glaciers holding out against the warming Arctic. Its slow advance stopped in 2013–the left image shows Taku in 2014–and researchers hoped the massive glacier would maintain its mass for a few decades at least. Instead, the glacier was retreating by 2018 and doing so with the highest mass loss ever recorded at the glacier. The 2019 image on the right shows the glacier’s visible losses.
For such a massive glacier–the largest in Juneau Icefield at nearly 1.5 km thick–to reverse fortunes so quickly is disturbing and serves as yet more evidence of climate change overriding natural cycles of advance and retreat. (Image credit: L. Dauphin/USGS; via NASA Earth Observatory)
In the ocean, breaking waves trap air into bubbles that then cluster into foam, but conventional simulations don’t capture this foaminess. For bubbles to cluster into foam, there has to be a force preventing — or at least delaying — their coalescence. Typically, this is caused by impurities in the water that help lower the surface tension and thereby lengthen the bubbles’ lifespans. When these features get added to simulation models, bubbles begin to cluster and breaking waves become foamy. (Image and video credit: P. Karnakov et al.)
Macro images of a soap film burst with color. Because the color comes from interference between light waves bouncing off the inner and outer surfaces of the soap film, the colors we see correspond directly to the thickness of the soap film. So the patterns we see reflect actual flows and variations inside the soap film. It’s not unusual for the patterning on a soap film to become increasingly complicated as the film drains and ages. Eventually black spots — areas too thin for interference to show visible colors — will appear and grow, and the film will pop.
If you’re interested in trying out some soap film photography for yourself, Professor Andrew Davidhazy has a nice description on his website of the set-up he used for this photo. (Image credit: A. Davidhazy; via Flow Vis)
The wingtip vortices of aircraft provide a veritable cornucopia of gorgeous imagery. There’s something inherently fascinating about these vortices that stretch behind moving aircraft. But four-engine aircraft add an extra twist to the imagery, as seen here.
With four engines, these aircraft produce four separate contrails, each of which acts like a streakline for the flow behind the wing. So what we see in these images is not the wingtip vortices themselves, but what their effect is on flow moving across different parts of the wing.
Nearby vortices influence one another, and one of the earliest models of aircraft physics takes advantage of this by modeling the wing itself as a series of vortices. Odd as it sounds, such models are quite good for capturing the basic flow physics behind a finite wing.
Using one of these models, Joseph Straccia explored the physics of a 4-engine aircraft’s wake (Image 4), predicting that the outboard engine contrails should initially move outward before getting rolled up and inward by the wingtip vortices. That’s exactly what we see in these images, particularly Image 1. The inboard contrails undergo less deflection, as expected since they are further from the wingtips. (Image credits: aircraft and contrails – JPC Van Heijst, J. Willems, and E. Karakas; modeling and submission – J. Straccia)
The Dutch have been exceptional water engineers for centuries, a necessity in a country where more than a quarter of its territory lies below sea level. After a devastating flood in the early 1950s, the country embarked on a decades’ long endeavor to build the massive Delta Works that now protect a large portion of the population from oceanic storm surges that would otherwise flood the countryside.
As part of their efforts to instill resiliency both along the coast and upstream, the Netherlands has shifted dykes, created floodplain habitats, and built water storage into new buildings. With communities around the world at greater flood risk than ever as our climate changes, the Netherlands serves as a shining example of what’s possible with proper planning and investment. (Video and image credit: TED-Ed)
