Celebrating the physics of all that flows with Nicole Sharp, Ph.D.
- Profile
Shock Waves in Flight
Schlieren photography allows visualization of density gradients, such as the sharp ones created by shock waves off this T-38 aircraft flying at Mach 1.1 around 13,000 ft. Although shock waves are relatively weak at this low supersonic Mach number, they persist, as seen in the image, at significant distances from the craft. The sonic boom associated…
Making Metal Water-Repellent
Chemical treatments can be used to render metals hydrophobic, causing water to bead on the surface rather than spreading to wet it. Treating the surface by immersing it in boiling water before applying the chemicals creates a nanoscale texture that accentuates the hydrophobicity. Even on a common metal like aluminum, this combination of texturing and chemical…
Turbulent Flames
The flames surrounding a burning tree stump flicker and billow in this image from photographer Serdar Ozturk. The chaotic motion of the flames is indicative of turbulence, a state of fluid flow known for its many scales. Note the range of lengthscales and structures in the fire. In turbulent flows, kinetic energy cascades from large scales, like the width of the top…
When Skittering Becomes Self-Propulsion
When liquids hit a surface much hotter than their boiling point, a thin layer of gas can form between the drop and surface, allowing the drop to glide along. This Leidenfrost effect is what makes drops of water skitter across a hot pan. But what happens when the pan isn’t flat? The video above shows…
Spiraling Out of Coils
Anyone who has drizzled honey or another viscous fluid onto a surface is familiar with the rope-like coiling behavior of some liquids. But did you know that same instability can create spirals of bubbles like in this photo? Such behavior is only seen for a narrow range of parameters within the gravitational regime of liquid…
Flapping Flags
Sometimes structural forces and aerodynamic forces combine to produce instabilities. One of the most common and familiar examples of this, a flag flapping in the breeze, remains extremely complex to analyze and describe. The flexibility of the flag, and its small but finite resistance to bending, combine with the variability of air flow around the…
The Red Crown
A drop of red dye falls into a thin layer of milk, forming a crown splash. Notice the pale edges of the droplets at the rim of the crown; this is milk that has been entrained by the original drop. The rim and satellite droplets surrounding the splash are formed due to surface tension effects,…
Rock Skipping Tips
Almost everyone has tried skipping rocks across the surface of a pond or lake. Here Professor Tadd Truscott gives a primer on the physics of rock skipping, including some high-speed video of the impact and rebound. In a conventional side-arm-launched skip, the rock’s impact creates a cavity, whose edge the rock rides. This pitches the…
Humpback-Inspired Turbine Blades
The bumps–or tubercles–on the edge of a humpback whale’s fins have important hydrodynamic effects on its swimming. Here dye is used to visualize flow over a hydrofoil with tubercle-like protuberances–a sort of artificial whale fin. Dye released from the peaks and troughs of the protuberances flows straight back in a narrow line before breakdown to…
Spin-Up
With the Oscars just over, it seems like a good time for some movie-trailer-style fluid dynamics. This video shows a rotating water tank from the perspective of a camera rotating with the tank at 10 rpm. Initially, the tank and its contents are at rest. When the tank begins spinning, the fluid inside responds. Pink…