Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Unsteady Rocket Nozzle
This numerical simulation gives a glimpse of flow inside an unsteady rocket nozzle. The nozzle is over-expanded, meaning that the exhaust’s pressure is lower than that of the ambient atmosphere. A slightly over-expanded nozzle causes little more than a decrease in efficiency, but if the nozzle is grossly over-expanded, the boundary layer along the nozzle…
Rocket Exhaust
A fiery jet of exhaust remains amid plumes of smoke as a Soyuz rocket lifts off from Baikonur Cosmodrome bound for the International Space Station. The lengthscales of such turbulence range from tens of meters to only millimeters, highlighting the incredible difficulty of accurately capturing and describing the fluid motion of a practical engineering problem.…
Supercomputed Fluids
Computational fluid dynamics and supercomputers can produce some stunning flow visualizations. Above are examples of turbulence, the Rayleigh-Taylor instability, and the Kelvin-Helmholtz instability. Be sure to check out LCSE’s website for more; they’ve included wallpapers of some of the most spectacular ones. (Photo credits: Laboratory for Computational Science and Engineering, University of Minnesota, #)
Microgravity Water Balloons
When a water balloon pops in microgravity, waves propagate from the initial point of contact and the final point of contact (where the balloon skin peels away). As these waves come inward toward one another, the water is compressed from its original potato-like shape into a pancake-like one. In most cases, surface tension will provide…
Viscous Fingers
High viscosity silicon oil is sandwiched between two circular plates. As the upper plate is lifted at a constant speed, air flows in from the sides. The initially circular interface develops finger-like instabilities, due to the Saffman-Taylor mechanism, as the air penetrates. Eventually the fluid will completely detach from one plate. (Photo credit: D. Derks,…
Magnus Force
Physics students are often taught to ignore the effects of air on a projectile, but such effects are not always negligible. This video features several great examples of the Magnus effect, which occurs when a spinning object moves through a fluid. The Magnus force acts perpendicular to the spin axis and is generated by pressure…
Vapor Cone
This stunning National Geographic photo contest winner shows an F-15 banking at an airshow and a array of great fluid dynamics. A vapor cloud has formed over the wings of the plane due to the acceleration of air over the top of the plane. The acceleration has dropped the local pressure enough that the moisture…
Liquid Lenses
Here astronaut Andre Kuipers demonstrates fluid dynamics in microgravity. A roughly spherical droplet of water acts as a lens, refracting the image of his face so that it appears upside down. The air bubble inside the droplet refracts the image back to our normal perspective again. (Photo credit: Andre Kuipers, ESA; via Bad Astronomy)
The Backward-Facing Step
This photo collage shows vortices shed off a backward-facing step. The flow is left to right. Here the flow is visualized using dye released in water. Initially, the vortex forms near the bottom of the step in the recirculation zone. Because flow over the top of the vortex is much faster than the flow beneath…
Homemade Hybrid Rocket Engine
In this video, Ben Krasnow details and demos a small hybrid rocket engine he built in his workshop. Hybrid rockets utilize propellants that are two different states of matter, in this case gaseous oxygen as the oxidizer and solid acrylic as the fuel. Krasnow’s verbal explanation of a convergent-divergent nozzle, used to accelerate flow to…