Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
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…
Dr. Seussian Mystery Fluid Could Have Saved Top Kill
Dr. Seussian Mystery Fluid Could Have Saved Top Kill Wired article about using non-Newtonian fluids to plug leaking oil wells as we featured previously.
Reader Question: National Committee for Fluid Mechanics Films
lazenby asks: Have you seen these guys? http://web.mit.edu/hml/ncfmf.html Yes, absolutely! Those videos, which date from the 1960s, are so useful that they’re still shown to undergraduates today. (Or at least they showed several of them to us when I was junior!) They can seem a bit slow by current standards, but the films are full…
Flow Visualization
[original media no longer available] This video gives a neat introduction to some common and uncommon techniques used to visualize fluid flows.
Smokestack Plumes
On a cold and windy day, the plume from a smokestack sometimes sinks downstream of the stack instead of immediately rising (Figure 1). This isn’t an effect of temperature–after all, the exhaust should be warm compared to the ambient, which would make it rise. It’s actually caused by vorticity. In Figure 2, we see a…
Airfoil-shaped Ice
I discovered this interesting bit of icing a couple years ago near the foot of a waterfall in Ithaca, NY. The predominant wind was always heading toward the falls (left to right in these pictures), while the falls were always throwing spray up into the wind. The result was that ice airfoils (center) formed in…
Thixotropic and Rheopectic Fluids
There’s more to non-Newtonian fluids than shear-thickening and shear-thinning. The viscosity of some fluids can also change with time under constant shear. A fluid that becomes progressively less viscous when shaken or agitated is called thixotropic. The opposite (and less common) behavior is a fluid that becomes more viscous under constant agitation; this is known…