Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
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Happy Valentine’s Day!
Here’s a potential flow field with heart-shaped streamlines, made just for you. Thank you to everyone for having helped made FYFD such a success over these 700 posts, whether by liking, reblogging, tweeting, or telling a friend. Happy Valentine’s Day! For the curious among you, the flow is a superposition of uniform flow, two sources, and…
Truck Vortices
The video above shows vortex rings of smoke ejected from the burning tire of a moving truck. Without seeing the damaged tire, it’s tough to pinpoint the cause with certainty, but here are a couple of ideas. Typically vortex rings are formed with a burst of air through a narrow orifice; this is, for example,…
Spiraling Ferrofluid
Here a ferrofluid climbs a spiral steel structure sitting on an electromagnet. Magnetic field lines emanating from the sculpture’s edges tend to push the ferrofluid out into long spikes–part of the normal field instability–but surface tension resists. The short, somewhat squat spikes we see are the balance struck between these opposing forces. Though known for…
Hummingbirds Singing with their Tail Feathers
Aeroelastic flutter occurs when fluid mechanical forces and structural forces get coupled together, one feeding the other. Usually, we think of it as a destructive mechanism, but, for hummingbirds, it’s part of courtship. When a male hummingbird looks to attract a mate, he’ll climb and dive, flaring his tail feathers one or more times. As…
Supersonic Oil Flow Viz
This image shows oil-flow visualization of a cylindrical roughness element on a flat plate in supersonic flow. The flow direction is from left to right. In this technique, a thin layer of high-viscosity oil is painted over the surface and dusted with green fluorescent powder. Once the supersonic tunnel is started, the model gets injected in…
Ink Drops
This super high resolution video (check the original on YouTube) by filmmaker Jacob Schwarz features slow motion diffusion of ink into water. The subtle differences in density between the ink and the water promote instabilities such as the Rayleigh-Taylor instability and its distinctive cascade of mushroom- or umbrella-like shapes. The mixing of two fluids seems…
Surface Tension in Action
Surface tension creates a glassy, smooth layer of water over U.S. swimmer Tyler Clary the instant before he surfaces as he competes in the backstroke. Surface tension arises from intermolecular forces between water molecules. In the bulk of the liquid, any given water molecule is being pulled on in every direction by the surrounding molecules,…
Droplet Springs
Prior to reaching terminal velocity, a falling droplet typically oscillates between a prolate shape (like an American football about to be kicked) and an oblate one (like that same football when thrown or carried). As explained by Minute Laboratory, this oscillation behaves very similarly to a mass on a spring. For a spring/mass system, the…
Reader Question: Frosty Cars
Reader Mike L asks: Why do I never see frost on my car when I park in a detached garage or under a carport? Great question! Frost forms on surfaces when their temperature drops below the freezing point of water and the dew point of the surrounding air. The water vapor in the air gets…
Dropping Through Strata
When a droplet falls through an air/water interface, a vortex ring can form and fall through the liquid. In this video, the researchers investigate the effects of a stratified fluid interface on this falling vortex ring. In this case, a less dense fluid sits atop a denser one. Depending on the density of the initial…