Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Hello, New Folks!
Lots of new faces around here at FYFD, so thanks, everyone, for spreading the word! As a reminder, you’re welcome to submit post ideas if you see something neat online and you can also ask any questions you have related to fluid mechanics, and I’ll do my best to answer them or find someone who…
Hole-Punch Clouds
These hole-punch clouds seen over Myrtle Beach, SC were probably caused by three aircraft flying in military formation. When airplanes pass through supercooled water vapor, the acceleration of air over the wing causes a pressure drop that can flash-freeze the water vapor, resulting in a localized snow shower. See National Geographic for more. #
How Ferrofluids Work
Here’s a ferrofluid video with a little more explanation about how ferrofluids work. Surfactants prevent the tiny magnetic particles suspended in the fluid from separating out when exposed to a magnetic field.
Marangoni Effect
Dyed milk pulls away after a drop of acetone is added. The acetone creates a gradient in the surface tension, which causes mass flow due to the Marangoni effect. See a video of the effect (or try it yourself at home!) here.
Geometrical Droplet Splashes
Sadly, this video shows no droplet impacts on a heart-shaped post, but maybe you can imagine what it would look like after seeing other geometrical shapes. Happy Valentine’s Day, guys!
High-Speed Leidenfrost Levitation
The Leidenfrost effect occurs when a liquid encounters a surface with a temperature much higher than its boiling point. Some of the liquid is instantly vaporized and then a droplet will skate across the surface on that vapor. This video shows the process at 3000 frames per second.
Volcanic Turbulence
One of the characteristics of turbulence is its large range of lengthscales. Consider the ash plume from this Japanese volcano. Some of the eddy structures are tens, if not hundreds, of meters in size, yet there is also coherence down to the scale of centimeters. In turbulence, energy cascades from these very large scales to…
Reader Question: Froude vs. Reynolds
@spooferbarnabas asks: I was wondering what the difference is between Froude’s number and Reynold’s number? they seem very similar Fluid dynamicists often use nondimensional numbers to characterize different flows because it’s possible to find similarity in their behaviors this way. The Reynolds number is the most common of these dimensionless numbers and is equal to…
The Pistol Shrimp’s Secret Weapon
The pistol shrimp (or pistol crab) is a finger-sized crustacean with a fluid dynamical superpower. When it snaps its claw, a jet of water shoots out so quickly (62 mph) that a low-pressure bubble forms in its wake. When the bubble collapses, it emits a bang and a flash of light in a process known…
Instability in a Jet
This photo shows the development of a flow instability in an axisymmetric jet. On the left, the jet is smooth and fully laminar, but, by the center of the photo, disturbances in the jet have grown large enough to distort the laminar profile. The jet is then in transition; by the right side of the…