Playing with a giant water balloon and high-speed cameras is like a giant experiment in surface tension, right up until the tensile strength of the balloon comes into play. The rippling in the balloon is reminiscent of the motion of droplet breakup or impact on superhydrophobic surfaces. (submitted by Daniel B)
Tag: fluid dynamics
DIY Non-Newtonian Fluids
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We’ve featured the non-Newtonian fluid oobleck here before, but it bears repeating as a fun and easy exercise for anyone to do at home or at school, especially with kids. For extra fun, try vibrating it, using it as liquid armor, or filling a pool and walking on it.
Meandering Mississippi
This satellite photo of the Mississippi River south of Memphis, TN shows how the river’s course has changed over time. When a river bends, the water near the inner bank flows faster than the water by the outer bank. This difference in speeds actually creates a vortical secondary flow in the boundary layer of the river that erodes sediment from the outer bank and deposits it on the inner bank. This increases the meander of the river bend. If this continues long enough, the river bend can get pinched off into an oxbow lake, like the ones scattered to either side of the current river path.
Tornado-Force Winds in a Wind Tunnel
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In order to demonstrate the effects of tornado-force winds, Fox News sent a reporter inside a wind tunnel and subjected him to 100 mph winds. Of course, actual measured winds in the recent storms topped 200 mph and four times the dynamic pressures the reporter experiences here. (via jerrodh)
How Not to Get Wet in the Rain
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Ever wonder how to minimize how wet you get if you’re caught in the rain without an umbrella? This lecture discusses just that problem and how to calculate an answer. I actually solved a version of this problem when studying for my PhD quals, only I first had to determine the terminal velocity of a rain drop (~10 m/s assuming a 4mm spherical drop) and work from there. We also had to compare moving upright to running at an angle. It makes for an interesting little diversion. (via physicsphysics)
Jet Breakup
A non-cylindrical stream falling through a slit nozzle exhibits the Plateau-Rayleigh instability, which drives a falling jet of fluid to break into droplets due to surface tension. The fingers formed off the falling stream may be a form of Rayleigh-Taylor instability. #
Seeing Blast Waves
This clip shows high-speed video footage of a blackpowder explosion. As the blast wave expands, the surrounding air is heated, which changes its index of refraction. The strength of this change is great enough that we can distinguish the edges of the expanding shock wave by the visual distortion they cause to the view beyond the explosion.
Flow Viz of a Locust
Smoke visualization in a wind tunnel reveals the airflow over a flying locust. Researchers are unraveling the aerodynamics of insect flight in order to produce better Micro Air Vehicles (MAVs) and miniature flying robots. #
Singing Dunes
Some sand dunes can “sing”, but not because of the wind! When loose sand slides down over harder, packed sand, a standing wave is formed, causing the entire surface of the dune to vibrate on a single frequency. We hear this as a musical note – typically an E, F, or G. (via io9)
(Image credit: C. Larson)
Upside-Down Umbrellas
When a heavier fluid is suspended over a lighter fluid (as with ink or food coloring in water), the interface between fluids is subject to the Rayleigh-Taylor instability. As the heavier fluid starts to sink, it forms “fingers”, which develop into mushroom-cap shapes as the fluid continues falling. Sometimes the shear stress between the heavier fluid and lighter fluid causes secondary Kelvin-Helmholtz instabilities as well. (Photo by Leonardo Aguiar)
