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

When a drop settles gently against a pool of the same liquid, it will coalesce. The process is not always a complete one, though; sometimes a smaller droplet breaks away and remains behind (to eventually do its own settling and coalescence). When this happens, it’s known as partial coalescence.

Here, researchers investigate ways to tune partial coalescence, specifically to produce more than a single droplet. To do so, they add surfactants to the oil layer surrounding their water droplet. The surfactants make the rebounding column of water skinnier, which triggers the Rayleigh-Plateau instability that’s necessary to break the column into more than one droplet. (Image and video credit: T. Dong and P. Angeli)

https://fyfluiddynamics.com/2024/10/tweaking-coalescence/

#2022gofm #coalescence #coalescenceCascade #fluidDynamics #instability #physics #PlateauRayleighInstability #science #surfaceTension #surfactant

Pour the Greek liquor ouzo into water, and your glass will billow with a milky, white cloud, formed from tiny oil droplets. The drink’s unusual dynamics come from the interactions of three ingredients: water, oil, and ethanol. Ethanol is able to dissolve in both water and oil, but water and oil themselves do not mix.

In this video, researchers explore the turbulent effects of pouring ouzo into water. In particular, pouring from the top creates a fountain-like effect, due to a tug-of-war between the ouzo’s momentum and its buoyancy. Momentum wants the ouzo to push down into the water, and buoyancy tries to lift it back up. For an extra neat effect, they also show what happens when the ouzo is confined to a 2D plane and what happens when momentum and buoyancy act together instead of oppositely. (Image and video credit: Y. Lee et al.)

https://fyfluiddynamics.com/2024/10/billowing-ouzo/

#2022gofm #buoyancy #flowVisualization #fluidDynamics #jets #miscibility #physics #science #turbulence

In our collective imagination, a raindrop is pendant shaped, wide at the bottom and pointed at the top. But, in fact, a falling raindrop experiences much more complicated shapes. Here, researchers blow a jet of air onto a still droplet, a good facsimile for a raindrop falling through the atmosphere. The jet of air first squishes the drop, then inflates it into a shape known as a bag. The thin sides of the bag stretch and eventually break, spraying tiny droplets. As the disintegration continues, the thick rim of the bag breaks up into big droplets. As the video demonstrates, viscosity and viscoelasticity can affect the break-up, too. (Image and video credit: I. Jackiw and N. Ashgriz)

https://fyfluiddynamics.com/2024/09/the-shape-of-rain/

#2022gofm #bag #droplets #fluidDynamics #instability #jets #physics #raindrops #science