Regelation Lets Glaciers Flow

Under the cold temperatures and immense pressures of a glacier, ice does not always behave in ways we’d expect. For example, cutting through ice using the pressure of a weighted wire does not break an ice block in two; as the wire passes through the ice, the melted water refreezes in its wake, leaving an intact block. Known as regelation, this process is one way that glaciers flow past obstacles in their path.

https://www.youtube.com/watch?v=EHRJxeGvTLs

Although many experiments demonstrate regelation for ice with temperatures near freezing, the process occurs in colder ice, too. A new study combines data across a wide range of temperatures with a new physical model of regelation to show how the process changes with temperature. It seems that relatively small temperature changes drastically affect how much meltwater forms around the wire and how slowly the ice refreezes. (Image credit: S. Ferrara; video credit: SciTube; research credit: C. Meyer et al.)

Physicists reversed the way energy flows through turbulence, bending an 80-year rule

https://www.martincid.com/science/turbulence-energy-flux-reversed-tensor-geometry-2/

#EnergyCascade #FluidDynamics #ScienceAdvances

#OnThisDay in 1826, physicist Georges Sire was born. His thesis on the “globular state of liquids” contributed to the early study of the #LeidenfrostEffect.

🔗Discover his contribution: https://www.leidenforce.eu/georges-sire-history-of-the-leidenfrost-effect

#HeatTransfer #FluidDynamics #HistoryOfScience

Infrasound Fire Suppression Goes Commercial

Sprinklers have long been the go-to fire protection for commercial properties and some residences. Dousing a fire in water not only puts out the flames but cools the surroundings and helps prevent reignition. But it requires complicated infrastructure and can damage buildings and their contents. Back in 2015, students were experimenting with an alternative fire extinguisher that used sound below the range of human hearing; now a company is pitching a version of that technology for replacing sprinklers.

As described by Ars Technica, this infrasound system can detect and put out a small kitchen fire in under a minute. But fire fighting experts warn that there’s a big difference between a fire small enough for a fire extinguisher to handle and the kinds of fires sprinklers put out. With lives at stake, the burden of proof is significant for Sonic Fire Tech and any other company that wants to get their infrasound “sprinkler” system cleared for use in buildings. (Image credit: I. Azevedo; via Ars Technica)

Real & simulated viscous fingering: Accidentally printed a digital negative on the wrong (non-absorbent) side of the transparency film, then folded it and the thick layer of ink produced this beautiful effect of branching traces. The two color prints in the back (soon also available for purchase) are variations of this project below, for which I've been simulating that effect via code...

https://mastodon.thi.ng/@toxi/115979123468886067

https://en.wikipedia.org/wiki/Saffman%E2%80%93Taylor_instability

#Fluidsim #FluidDynamics #Inkjet #DigitalNegative #PrintMaking

Bubble bursting changes dramatically when bubbles have neighbors. In dense rafts, collapsing cavities produce thinner, faster jets and droplets up to 5× smaller than isolated bubbles.

A collective effect that could reshape how we model sea spray aerosols.

🔗 https://doi.org/10.1103/7ygz-2s6s

#FluidDynamics #BubbleBursting #Aerosols #Capillarity #Physics

Why does water have such an unusually high surface tension?

This study links the effect to molecular-scale interactions and hydrogen-bond dynamics, offering new insight into one of water’s most fundamental properties.

🔗 https://pubs.aip.org/aip/pof/article-abstract/38/4/042007/3386944/Molecular-driven-extreme-surface-tension-of-water?redirectedFrom=fulltext

#SurfaceTension #Water #MolecularPhysics #FluidDynamics #interfaces

On Dolphin Turbulence

Dolphins are such fast and agile swimmers that, naturally, scientists have long wanted to understand how they swim so well. A recent study draws on numerical simulation to analyze the flow a dolphin creates when flapping its tail.

The resulting flow is highly turbulent–researchers were only able to simulate up to a fraction of a dolphin’s actual Reynolds number–with both large-scale vortices and a cascade of smaller ones. The largest vortices, shown here in white, form on the upper and lower surface of the dolphin’s tail, then slide off the tail in a vortex ring. It’s these vortex rings, the researchers found, that provide the bulk of a dolphin’s thrust.

The smaller-scale vortices, in contrast, get formed by the large vortices, and they make little to no contribution to the dolphin’s propulsion. Interestingly, these results suggest that we might be able to describe the propulsion of dolphins and other highly turbulent swimmers by focusing only on the largest scales in the flow. (Video, image, and research credit: Y. Motoori et al.; via Ars Technica)

What does turbulence look like in a quantum fluid?

Researchers are exploring how Bose–Einstein condensates shift from weak to strong turbulence, revealing how energy cascades behave when quantum mechanics takes over.

🔗 https://physicsworld.com/a/what-happens-when-a-bose-einstein-condensate-becomes-turbulent/

#QuantumPhysics #Turbulence #BEC #FluidDynamics #physics

Seeking Quieter Supersonic Flight

Supersonic flight over the U.S. has been banned by all non-military aircraft for more than fifty years. The ban gained momentum in the 1960s after test programs over St. Louis and Oklahoma provoked public outcry. But NASA’s X-59 aircraft is working to lift the ban by softening the sonic booms that encouraged the ban in the first place. Although it hasn’t been tested at supersonic speeds yet, pilots are putting the sharp and skinny X-59 through its paces, slowly widening the flight envelope.

https://www.youtube.com/watch?v=gR4Xuslczoo

In the video above, NASA shares footage of some of the recent test flights, including various maneuvers like phugoids, banking rolls, flutter, and landing gear tests. Pay close attention to the pilot’s view and the radio chatter, and you’ll hear that they’re hovering around Mach 0.98 in some cases–just underneath the point of generating a shock wave around the aircraft. It will be neat to see what happens when they finally do go supersonic. Will it be as quiet as promised? (Video credit: NASA; image credit: NASA/L. Losey; see also NASA; via Gizmodo)