Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
“Dendrite Fractals”
In this short film from the Chemical Bouillon team, dark ink drops spread in dendritic fractal patterns after being deposited on an unknown transparent liquid. Although the patterns look similar to those of the Saffman-Taylor instability, I suspect what we see here is actually driven by surface tension and not viscosity. The authors describe the…
Dunes Avoid Collisions
The speed at which a dune migrates depends on its size; smaller dunes move faster than larger ones. That speed differential implies that small dunes should frequently collide into and merge with larger dunes, eventually forming one giant dune rather than a field of smaller separate ones. But that’s not what we observe in nature.…
Sunlight Is Older Than You Think
Joe Hanson over at “It’s Okay to Be Smart” has a great video on the random walk photons have to make to escape the core of the sun and other stars. Because the high-energy photons born in the star’s core have to bounce their way out rather than flying in a straight line, those photons…
Kicking Droplets
Moving the surface a droplet sits on creates some interesting dynamics, especially if the surface is hydrophobic. That’s what we see here with these droplets launched off an impulsively-moved plate. On the left, the drop has some limited contact with the plate and it takes time for the droplet to completely detach. When accelerated, the…
Listening to a Bubble’s Pop
Sound is an important aspect of many flows, from the scream of a rocket engine to the hum of electrical wires vibrating in the wind. Critically, those sounds carry important information about the flow. A new study extends these acoustic diagnostics to the popping of soap bubbles. When a hole opens in a soap bubble,…
The Cricket’s Chirp
Growing up, my summer nights often featured a chorus of crickets and bull frogs. Even now, the sound of those chirps reminds me of home. So how do crickets make their calls? As this video shows, it’s a matter of scraping the hard edge of one wing along a tiny series of spines, similar to…
Frozen Wavelets
Photographer Eric Gross captured these surreal alpine landscapes in Colorado’s Rocky Mountains. Although the lake’s surface appears to have frozen waves, the prevailing theory is that these mounds and divots occur when snowdrifts form atop the lake, melt and refreeze. Over multiple melting and freezing cycles, the lake builds up with what appear to be…
Spin Cycle
Rotational motion is a great way to break up liquids, as anyone who’s watched a dog shake itself dry can attest. That same centrifugal force is what allows this rotary atomizer to break liquids into droplets. Relative to the photos above, the atomizer spins in a counter-clockwise direction. This motion stretches the fluid flowing off…
Colorful Dissipation
Colorful eddies swirl in this short video from photographer Karl Gaff. Formed near the boundary at the bottom of the frame, these eddies act to dissipate some of the energy in the flow. Structures like these are key in turbulent flows, where energy must pass from large eddies to smaller and smaller ones until they…
Nitro Bubble Cascades
Fans of nitro beers — particularly Guinness’ stout — have probably noticed the fascinating cascade of bubbles that form as the beer settles. It’s a non-intuitive behavior — bubbles rise since they’re lighter than the surrounding fluid. So why do the bubbles appear to sink in these beers? There are several effects at play here. Firstly, overall…