Observation de l'écoulement d'un fluide autour d'une section cylindrique

#cavitation

Animation: Synchronisationsschema EuXFEL-Messzeit p2207

https://tube.tchncs.de/w/qjiXyDRuCf6kJZf1TtEWAE

“Broken Water, Like Broken Glass”

How can you break water? By accelerating it so quickly that the pressure drop forms cavitation bubbles. Here, a steel piston rests against a transparent plate, all underwater. When a hammer strike accelerates the piston away at around 1000g, the severe pressure drop tears the water into bubbles (bottom, left). As the bubbles expand, the nearby piston squishes them into pancakes (bottom, center). As they continue growing, the bubbles press into one another, squeezing thin ridges of water between them. The result (center) resembles broken glass. (Image credit: J. da Silva et al.)

Aus dem Archiv:

Ein roter Laserpuls hat in Wasser eine explodierende Plasmablase gezündet.
Von links erfasst ein hochbrillanter Röntgen-Freie-Elektronen-Laserblitz die Szene holografisch.
Ein Mikrofon zeichnet akustische Signale auf.
An der Wand sehen wir die entstehenden Blasen zu verschiedenen Zeitpunkten.

(nächster Trot: Link zum Video)

#Cinema4D #PhysikEdu #Cavitation #EuXFEL

What Limits a Siphon

Siphons are a bit mind-boggling for anyone who has internalized the idea that water always flows downhill. But gravity actually allows a siphon’s water to flow up and over an obstacle, provided certain conditions are met. Steve Mould digs into the details of those conditions in this video, where he searches for the maximum height a siphon can reach.

A quick note on terminology: Steve explains that the siphon breaks when water near the top starts “boiling.” Other sources may use the term “cavitating” for this sudden phase change. There’s not–to my knowledge–a generally-agreed-upon definition that clearly distinguishes between boiling and cavitation in this situation. Whichever term you use, the water in the siphon doesn’t care; either way, it’s experiencing a local pressure that’s so low that it switches from a liquid state (where it can resist tensile forces) to a gaseous one (where it cannot resist tension). (Video and image credit: S. Mould)

#cavitation #DIYFluids #fluidDynamics #physics #science #siphon

Inside Cuttlefish Suction

Cuttlefish, like many cephalopods, catch prey with their tentacles. Suction cups along the tentacle help them hold on. In this video, researchers share preliminary studies of what goes on inside these suction cups as they’re detached. The low pressures inside the suction cup cause water to vaporize, temporarily. As seen for both the cuttlefish and a bio-inspired suction cup, small bubbles form inside the attached cup, coalesce into larger bubbles, and then get destroyed in the catastrophic leak that occurs once part of the suction cup detaches. (Video and image credit: B. Zhang et al.)

#biology #bubbleCollapse #cavitation #cuttlefish #flowVisualization #fluidDynamics #physics #science #suction

I have always thought of #cavitation (the formation and rapid collapse of bubbles due to a liquid pressure drop), from an #engineering standpoint, as a problem that needs to be mitigated or avoided. But TIL that there are applications for which induced cavitation is useful... and it could be generated with that trusted sci-fi staple - #laser.

Link: https://www.sciencedirect.com/science/article/pii/S0030399223011052

Cavitation Near Soft Surfaces

Collapsing cavitation bubbles are sometimes used to break up kidney stones, and they may find other uses in medicine as well. Here, researchers investigate the collapse of laser-triggered cavitation bubbles near tissue-mimicking hydrogel. The bubbles take on a very different form than they do near solid surfaces. Near hydrogel, the bubbles become mushroom-shaped. During their collapse, they release a rainy microjet that moves at nearly 2,000 meters per second! Even at 5 million frames per second, the jet is practically a blink-and-you-miss-it phenomenon. (Image and video credit: D. Preso et al.)

#2022gofm #cavitation #fluidDynamics #jets #physics #science

Dry Plants Warn Away Moths

Drought-stressed plants let out ultrasonic distress cries that moths use to avoid plants that can’t support their offspring. In ideal circumstances, a plant is constantly pulling water up from the soil, through its roots, and out its leaves through transpiration. This creates a strong negative pressure — varying from 2 to 17 atmospheres’ worth — inside the plant’s xylem. If there’s not enough water to keep the plant’s inner flow going, cavitation occurs — essentially a tiny vacuum bubble opens in the xylem. That cavitation isn’t silent; it creates a click at ultrasonic frequencies above human hearing. But just because we don’t hear it doesn’t mean that sound goes unheard.

In fact, recent research suggests that, not only do moths hear the plant’s cavitation cries, female moths will avoid laying eggs on a healthy plant that sounds like it’s cavitating. Evolutionarily, this makes sense. Hatchlings rely on their birth plant for food and habitat; if an adult moth picks a dying, drought-stressed plant, its offspring won’t survive. It pays to be sensitive to the plant’s signs of distress. (Image credit: Khalil; research credit: R. Seltzer et al.; via NYTimes)

#acoustics #biology #cavitation #fluidDynamics #moths #physics #plants #science #transpiration