Search results for: “waves”

Slow Mo Pulse Jet Engine
Pulse jet engines rely on their shape to maintain combustion without moving parts. The pressure waves that travel through the engine pump fresh oxygen into the combustion chamber and then ignite it with exhaust remaining from the last cycle. In this Slow Mo Guys video, we get to see that process in action. It’s a pretty neat view of combustion in a working engine, but these guys are definitely not going to win any awards for safety measures. Seriously, don’t try this at home! (Image and video credit: The Slow Mo Guys)
January 11, 2021
Seismic Events Reveal Ocean Temperatures
Decades ago, researchers proposed sending sound waves through the ocean to measure its temperature. Although the technique worked, it ran into noise pollution issues, but now it’s back, using naturally-occurring seismic events as the sound source.
When fault lines shift, they generate seismic waves that travel through the ocean as sound. When they reach a land mass, the waves get converted back into seismic energy that’s then picked up by a receiver. Knowing the distance from the source to the receiver and the time necessary for the wave to travel, scientists can then determine the average temperature of the water based on the speed of sound.
The technique can track temperature changes down to thousandths of a degree. Based on more than a decade of seismic data from the Indian Ocean, researchers found almost double the temperature increase measured by a different sensor network. (Image and video credit: Science; research credit: W. Wu et al.; submitted by Kam-Yung Soh)
January 5, 2021
Jets Beneath Leidenfrost Drops
When a droplet impacts, it’s not unusual for converging ripples to form an upward jet, like the one seen here. But under the right circumstances, jets can form downward, too. This study looks at the ultrafast jets that can form beneath an impacting Leidenfrost drop.
These Leidenfrost drops are striking a surface much hotter than their boiling point, so a large vapor cavity forms quickly beneath them. Using x-ray imaging, the researchers were able to capture the dynamics of this cavity’s formation and collapse (Image 2). The field of view in the animation shows only a portion of the drop’s cavity, so Image 3 may help you orient relative to the drop at large.
Initially, we see the center of the droplet hitting the surface, followed by the fast growth of a vapor cavity. Rippling capillary waves converge on top of the cavity, creating a pinch-off. From there, a bubble rises up while a fast jet shoots downward. (Image credit: water jet – A. Min, others – S. Lee et al.; research credit: S. Lee et al.)
December 7, 2020
“The Unseen Sea”
San Francisco’s picturesque fogs form “The Unseen Sea” in Simon Christen’s timelapse. Viewed at the right speed, the motion of clouds becomes remarkably ocean-like, with standing waves and surges against the hillside like waves crashing on a beach. Clouds in air don’t have the same surface tension effects as water waves in air, but, for the most part, the physics of their motion is the same, which is why they look so alike. (Image and video credit: S. Christen)
November 20, 2020
Dead Water
In the days before motorized propulsion, sailors would sometimes find themselves slowed nearly to a stop by what they called ‘dead water‘. As discovered in laboratory experiments over a century ago by Vagn Walfrid Ekman, the dead water phenomenon occurs where a layer of fresh water exists over saltier water. The ship’s motion generates internal waves in the salty layer, which in turn causes substantial additional drag on the boat. In a related phenomenon, named for Ekman, the internal waves generated by a boat’s initial acceleration cause its speed to fluctuate.
While these phenomena have little effect on today’s shipping, they can be relevant for swimmers in areas like harbors and fjords where fresh water meets the sea. And their effects were undoubtedly substantial for much of history. There is even speculation that dead water might have caused the defeat of Mark Antony and Cleopatra’s superior navy at the hands of Octavian’s smaller ships in the Battle of Actium. (Image credit: M. Blum; research credit: J. Fourdrinoy et al.; via Hakai Magazine; submitted by Kam-Yung Soh)
November 18, 2020
Coalescing Drops
This year’s Nikon Small World in Motion competition was won by fluid dynamics! The first place video shows droplets on a superhydrophobic surface coalescing. The droplets are a mixture of water and ethanol. Their initial merger creates a ripple of waves that’s followed by a ghostly vortex ring that jets into the interior. Previous research on coalescence during impact shows jets driven by surface tension but the jet here doesn’t appear to be confined to the surface. (Image and video credit: K. Rabbi and X. Yan; via Nature; submitted by Kam-Yung Soh)
November 13, 2020
Colorful Kelvin-Helmholtz Clouds
Like breaking waves at the beach, these wavy clouds curl but only for a moment. The photo was captured near sunset on a late August evening in Arlington, MA. This short-lived cloud shape forms due to the Kelvin-Helmholtz instability, which is driven by shear forces between two layers of air moving at different speeds. The situation is a common one in the atmosphere, where air layers at altitude move in different directions and at different speeds. Most of the time we cannot see the curls that form between these air layers because of air’s transparency. But occasionally the mismatch happens right at a cloud layer and the condensation of the cloud gets pulled into these distinctive curls. (Image credit: B. Bray; submitted by Mark S.)
November 12, 2020
Understanding Stars’ Seismology
Our understanding of Earth’s interior is based mostly on observations of seismic waves, which travel differently through our rocky crust and the molten core. Scientists similarly use seismic waves in stars to determine their interiors. But the pressure and temperature conditions in stars are far beyond anything we have here on Earth, which makes predicting how waves will travel in such exotic material difficult.
To better understand these extreme temperatures and pressures, scientists are using Lawrence Livermore’s National Ignition Facility (NIF) to mimic conditions similar to the outer envelope of a white dwarf star, like the one shown in the center of the image above. NIF’s laser array – shown as the blue lines in the artist’s conception above – can generate spherical shock waves that, as they converge on a solid sample, create pressures as high as 450 Mbar, more than 400 million times sea level atmospheric pressure here on Earth. Although the shock wave takes only 9 ns to travel across the sample, it’s enough to give researchers a glimpse into star-like conditions. (Image credit: NASA/ESA/C. O’Dell/D. Thompson, Lawrence Livermore National Laboratory; via Physics Today)
November 10, 2020
“Colors”
Paint, soap, bleach, oil, and oat milk combine to create the gorgeous colorscapes of Thomas Blanchard’s short film “Colors”. Watch as droplets burst and waves of color flow past. It’s a lovely break from whatever you’re dealing with at the moment, and at less than 3 minutes long, you can spare the time! (Image and video credit: T. Blanchard)
October 23, 2020
Psychedelic Soap Film
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)
October 2, 2020

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