This high-speed schlieren video reveals the ignition of a butane lighter. The schlieren optical technique exaggerates differences in refractive index caused by density variations, enabling experimentalists to see thermal eddies, shock waves, and other phenomena invisible to the naked eye. Here a jet of butane shoots upward from the lighter as a valve is released. Then the spark from the lighter ignites the butane gas near the bottom of the jet. A flame front the propagates outward and upward, completing the lighting process. (submitted by @Mark_K_Quinn)
Search results for: “waves”
Breakup of an Annular Sheet
A thin annular sheet of water is sandwiched between two concentric air streams. This airflow on either side of the water causes shearing and Kelvin-Helmholtz-type instabilities develop, causing the sinuous waves along the water surface. Periodic behavior of the sort observed here is frequently observed in fluid mechanical instabilities. #
Wave Clouds Over Alabama
Last week, Birmingham, Alabama got treated to a special cloudy day, thanks to some Kelvin-Helmholtz waves, shown above. When a layer of faster moving fluid shears a slower moving fluid, this instability can form and cause some spectacular mixing. In this case, the lower, slower fluid was cool and moist enough to contain clouds, enabling us to see the effect with the naked eye. The same mechanism is responsible for the shape of breaking ocean waves and can even be seen in the atmospheres of gas giants like Saturn and Jupiter. (submitted by David B)
Water Balloon Physics
[original media no longer available]
This video explores some of the physics behind the much-loved bursting water balloon. The first sections show some “canonical” cases–dropping water balloons onto a flat rigid surface. In some cases the balloon will bounce and in others it breaks. The bursting water balloons develop strong capillary waves (like ripples) across the upper surface and have some shear-induced deformation of the water surface as the rubber peals away. Then the authors placed a water balloon underwater and vibrated it before bursting it with a pin. They note that the breakdown of the interface between the balloon water and surrounding water shows evidence of Rayleigh-Taylor and Richtmyer-Meshkov instabilities. The Rayleigh-Taylor instability is the mushroom-like formation observed when stratified fluids of differing densities mix, while the Richtmyer-Meshkov instability is associated with the impulsive acceleration of fluids of differing density.
Bow Shock over a Perforated Plate
This schlieren image shows a sphere traveling at Mach 3 over a perforated plate. The bow shock in front of the sphere is clearly visible, as is its reflection off the plate. The pressure caused by the bow shock produces a series of spherical acoustic waves below the plate. A tiny vortex ring moves downward from each hole, followed at the right by a secondary ring moving upward from the holes in the plate. (Photo credit: U.S. Army Ballistic Research Laboratory; reprinted in Van Dyke’s An Album of Fluid Motion)
Vibration-Induced Atomization
Atomization–breaking a liquid into a fine spay of droplets–is common in engines, printers, and in the shower. Here a droplet of water is placed on a thin metal diaphragm that is vibrated at 1 kHz with increasing vibrational amplitude. Capillary waves form on the droplet, and once a critical vibrational amplitude is achieved, tiny droplets are ejected. Full atomization of the original droplet is achieved in about 0.3 seconds real-time. #
Rocket Engine Testing
Rocket engine tests usually feature a distinct and steady pattern of Mach diamonds in their exhaust. This series of reflected shock waves and expansion fans forms as a result of the exhaust pressure of the rocket nozzle being lower or higher than ambient pressure. A rocket will be most efficient if its exhaust pressure matches the ambient pressure, but since atmospheric pressure decreases as the rocket gets higher, engines are usually designed with an optimal performance at one altitude.
Astronomical Jets
Researchers have pieced together Hubble images of jets from newborn stars into timelapse movies that reveal the interstellar fluid mechanics responsible for the formation of stars like our sun. These jets stream out clumps of matter that has fallen on the new star. When faster moving eddies impact slower ones, bow shocks can form, much like shockwaves running before an airplane. See more HD video of these jets and bow shocks here. #
Sound and Harmonics
The vibrations we perceive as sound, whether in air, water, or any other fluid, are tiny pressure waves emanating from a source, transmitting like ripples across a pond, and finally being caught by our ears and translated by our brains. In this video, the mechanisms and mathematics of sound and harmonics are explained. Although we’re most familiar with these concepts in acoustics, the same principles are used when studying other oscillatory motions, including pendulums, mass-spring systems, disturbances in boundary layers, and the vibrations of a diving board. All of these things rely on the same fundamental principles and mathematics.
Computational Shock Compression
[original media no longer available]
Computational modeling can help verify and visualize experimental results, as in this video of supersonic flow. Oak Ridge National Laboratory produced the work as part of a project using shock compression and turbines to capture carbon dioxide gas. Shock waves and velocity profiles are shown throughout the computational field, and velocity isosurfaces paint a telling portrait of the complicated flow pattern. Wired Science features other award-winning simulation videos, many of which also feature fluid dynamics. #
