Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
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Fluids Round-up – 20 October 2013
Some very cool fluids applications in this week’s fluids round-up. On to the links! Like many colleges, MIT has campus myths about those unbelievably windy spots. But, unlike many others, they have a CFD analysis deconstructing the myths. Even rocks can behave like fluids sometimes. Check out this article from @s_i_r_h_c on fluid instabilities left behind in rocks. Reader Julian…
The Cheerios Effect and Tiny Swimmers
Anyone who has eaten a bowl of Cheerios is familiar with the way solid objects floating on a liquid surface will congregate. This is a form of capillary force driven by the wetting of the particles, surface tension, and buoyancy. Using ferromagnetic particles and a vertical magnetic field, one can balance capillary action and lock…
Overflowing Foam
Hitting a glass bottle full of a non-carbonated drink can shatter the bottle due to cavitation, but doing the same with a carbonated beverage can make the bottle overflow with foam. The video above breaks down the physics of this bar prank. It all begins with nucleation and the tiny bubbles of carbon dioxide that…
Self-Propelled Droplets
Leidenfrost drops hover and move above hot surfaces on a thin layer of their own vapor. Over a flat surface, this vapor flows radially out from under the droplet, but creating rachets in the surface forces the vapor to flow in a single direction. The vapor then acts like exhaust, generating propulsion in the droplet…
Shaping and Levitating Droplets
Opposing ultrasonic speakers can be used to trap and levitate droplets against gravity using acoustic pressure. Changes to field strength can do things like bring separate objects together or flatten droplets. The squished shape of the droplet is the result of a balance between acoustic pressure trying to flatten the drop and surface tension, which tries…
Fluid Juggling
It’s that time of the year – the 2013 APS Division of Fluid Dynamics meeting is not far off, and entries to this year’s Gallery of Fluid Motion are starting to appear. This week we’ll be taking a look at some of the early video submissions, beginning with one that you can recreate at home.…
Fluids Round-up – 13 October 2013
There were so many good fluids links this week that I decided for an off-week fluids round-up. Here we go! Jefferson Lab has a cool demo on how to make a cloud chamber using dry ice, isopropyl alcohol, and a radioactive source. There is all kinds of fun physics to explain in this one! io9 has a great…
Lakes Upon Glaciers
Supraglacial lakes–ephemeral bodies of water that form atop glaciers–can form and empty in a matter of hours. The lakes typically empty either by overflowing their banks or by discharging through a moulin, a well-like crevasse in the ice. When this happens, the water from the lake drains into the bed beneath the glacier, acting like…
Schlieren in Flight
Schlieren photography is a common method of visualizing shock waves in wind tunnel experiments, but it’s much harder to pull off for aircraft in the sky. This video from NASA shows off some stunning work out of NASA Dryden capturing schlieren video of shock waves from a F-15B aircraft at Mach 1.38. You’ll notice that…
Droplet Collisions
When droplets collide, there are three basic outcomes: they bounce off one another; they coalesce into one big drop; or they coalesce and then separate. Which outcome we observe depends on the relative importance of the droplets’ inertia compared to their surface tension. This is expressed through the dimensionless Weber number, made up of density,…