FYFD

Category: Phenomena

  • Oceanic Swirls

    Oceanic Swirls

    Mixing of surface waters with deeper ocean currents brings together the minerals and nutrients used by phytoplankton, resulting in gorgeous swirls of color in the ocean.  These phytoplankton blooms are most common in the spring and summer, and while lovely, can be harmful to other marine life, either through the production of toxins or by depleting the waters of oxygen. Because the phytoplankton move according to the wind and waves, they can also form a sort of natural flow visualization. (Photo credit: ESA)

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    While FYFD is not blacking out for SOPA/PIPA, we would like to take a moment to register our protest and encourage those of you who are Americans to take a moment to let Congress know that you don’t approve of these bills.  Although we agree that protection of copyright holders rights is important, the measures proposed in these bills reach far beyond that line.  FYFD, as a site that reposts photos and videos primarily created by others, could be taken down as a result of these bills, despite the purpose of the website as a tool for educational outreach and dissemination of science. Please support a free and uncensored Internet!

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    Dove in Flight

    This spectacular high-speed video shows a dove in flight. Note how its wings flex through its stroke and the way the wings rotate over the course of the downstroke and reversal. There is incredible beauty and complexity in this motion.  The change in wing shape and angle of attack is what allows the bird to maximize the lift it generates. Note also how the outer feathers flare during the downstroke. This promotes turbulence in the air moving near the wing, which prevents separated flow that would cause the dove to stall. (See also: how owls stay silent. Video credit: W. Hoebink and X. van der Sar, Vliegkunstenaars project)

  • Inside a Blender

    [original media no longer available]

    High-speed video visualizes the complicated flow field inside a blender.  Note that the video is placed in reverse for artistic effect.  This flowfield is clearly too turbulent for reversible flow. That said, it is possible to mix two fluids and then unmix them, under the right circumstances.

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    The Invisible Forces Behind a Lighter

    This high-speed schlieren video reveals the ignition of a butane lighter.  The schlieren optical technique exaggerates differences in refractive index caused by density variations, enabling experimentalists to see thermal eddies, shock waves, and other phenomena invisible to the naked eye. Here a jet of butane shoots upward from the lighter as a valve is released. Then the spark from the lighter ignites the butane gas near the bottom of the jet. A flame front the propagates outward and upward, completing the lighting process. (submitted by @Mark_K_Quinn)

  • Cloud Streets from Space

    Cloud Streets from Space

    Cloud streets flowing south across Bristol Bay hit the Shishaldin and Pavlof volcanoes, which part the air flow into distinctive swirls called von Karman vortex streets. As air flows around the volcano, a vortex is shed first on one side, then the other. Although the usual example for this type of flow is the wake of a cylinder, vortex streets can extend behind any non-aerodynamic body immersed in a flow. The same phenomenon is responsible for the singing of power lines in the wind.  As astronaut Dan Burbank observes, “It’s classic aerodynamics, but on a thousands of miles scale.” (Photo credit: Dan Burbank, NASA)

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    Separation and Stall

    This flow visualization of a pitching wind turbine blade demonstrates why lift and drag can change so drastically with angle of attack. When the angle the blade makes with the freestream is small, flow stays attached around the top and bottom surfaces of the blade. At large (positive or negative) angles of attack, the flow separates from the turbine blade, beginning at the trailing edge and moving forward as the angle of attack increases. The separated flow appears as a region of recirculation and turbulence. This is the same mechanism responsible for stall in aircraft. (Submitted by Bobby E)

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    Viscoelastic Fluids in Space

    In honor of astronaut Don Pettit’s launch to the International Space Station (and in the hope that he’ll do more neat microgravity fluids demonstrations while in space!), here’s a look a the behavior of viscoelastic fluids in microgravity. The elasticity of these fluids means that, when strained, the fluid deforms instantaneously and then returns to its initial shape when the strain is removed. Pettit demonstrates both Plateau-Rayleigh instability behavior, where a column of fluid breaks apart due to surface tension variations, and die swell, where a fluid jet expands beyond the diameter of nozzle from which it was extruded. Such swelling is commonly caused by the stretching and relaxation of polymers in the fluid as they react to forces caused by the nozzle opening.

  • Wave Clouds Over Alabama

    Wave Clouds Over Alabama

    Last week, Birmingham, Alabama got treated to a special cloudy day, thanks to some Kelvin-Helmholtz waves, shown above. When a layer of faster moving fluid shears a slower moving fluid, this instability can form and cause some spectacular mixing. In this case, the lower, slower fluid was cool and moist enough to contain clouds, enabling us to see the effect with the naked eye. The same mechanism is responsible for the shape of breaking ocean waves and can even be seen in the atmospheres of gas giants like Saturn and Jupiter. (submitted by David B)

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    Leaping Shampoo

    The Kaye effect is a neat phenomenon associated with falling shear-thinning non-Newtonian fluids like shampoo or hand soap.  As the falling liquid piles up after hitting a solid surface, it ejects streams of fluid upwards.  The effect usually only lasts for a few hundred milliseconds, but it is possible to see it at home without a high-speed camera if you pay close attention.  More detailed physics of the effect are discussed in this previously featured video.

  • Glass Isn’t a Fluid

    Glass Isn’t a Fluid

    Mark R writes:

    Glass is a Fluid, Too
    Post complex equations regarding how long it would take a certain window to flow, and post pictures of sunken glass. This would be educational.

    This is a pretty widespread myth. Actually, glass is not a fluid and does not behave like one as long as it is below the glass transition temperature. It’s a bit difficult to classify glass under the traditional categories for a solid due to its phase transition behavior and its lack of crystallization, but it is usually classed as an amorphous solid.

    The observation that old panes of glass tend to be thicker at the bottom is usually used as evidence that glass flows over the centuries, but this assumes that the glass was flat to begin with. However, glassblowers at the time usually made panes by spinning molten glass to create a round, mostly even flat, which was then cut to fit. Although spinning made the glass mostly flat, the edges of the disc tended to be thinner. When installed, the glass was typically placed thicker side down for stability purposes. One researcher even calculated the time period necessary for glass to flow and deform at ordinary temperatures as 10^32 years–longer than the age of the universe.

    If that is not convincing, consider this: if glass flows at a rate that’s discernible to the naked eye after a couple of centuries, then the effect of this deformation should be extremely noticeable in antique telescopes since a slight change in the lens’ optical properties should dramatically affect performance. But no such degradation occurs. (Photo credit: Vincent van der Pas)