This stereo 3D photo shows the Worthington jet ejected when a droplet impacts a pool. The flat crowning drop is formed from an ejected droplet colliding with a falling droplet.
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Combustion
Fluid dynamics are vital to combustion. Like here, many practical flames–such as those responsible for internal combustion in automobiles, jet engines, and rockets–are turbulent. The turbulence aids mixing of the fuel and oxidizer, resulting in more complete combustion and greater efficiency. #
Liquid Acrobatics
Imagine blowing through a straw into a nearly empty glass–we probably all did this as children and sent water, milk, and soda flying everywhere! In essence, this video shows that same act, but filmed by a high-speed camera. The “straw” blows a steady stream of helium into a shallow pool of silicone oil and slowly moves so that the angle the straw makes with the pool changes. As the angle changes, different regimes are visible. First waves appear on the surface of the pool, then a bulge forms, which develops into a droplet stream, then on into the chaos of bubbles and jets. It’s good I couldn’t see this in slow motion as a child or I would have never used my straw for drinking!
Rocket Exhaust
This image of the Apollo 11 launch shows the Saturn V’s underexpanded nozzle (identifiable by the excessive width of the exhaust jet) shortly after liftoff. The faint diamond shape of the exhaust is a series of shock waves and expansion fans that equalize the exhaust pressure to the ambient. In general, a rocket nozzle is most efficient when it expands the exhaust to ambient pressure, but, since ambient pressure changes with altitude, designers have to choose a particular altitude for peak efficiency or design a nozzle capable of changing its shape with altitude.
Laminar Flow Control
On Wednesday, March 30, 2011 at 3:00 EDT NASA engineers are holding an online chat about a current project to achieve laminar flow control on business jet-class airplanes. Keeping flow over an airplane’s wings laminar could decrease the total drag on an airplane by as much as 15%. In particular, this project involves placing tiny hockey-puck-shaped discrete roughness elements (DREs) along the front of the wing. These DREs are positioned such that they perturb the mean-flow over the wing at a higher frequency than the naturally most unstable frequency; as a result, flow actually remains laminar over a greater extent of the wing than would normally be the case. For more on the technical ideas, see this NASA blog post or feel free to ask questions in the comments. #
Full disclosure: This project is being conducted in joint with professors with whom I work, and the subject matter is related to my own research.
Air Force Gears Up For Hypersonic Missile Test
Air Force Gears Up For Hypersonic Missile Test
The U.S. Air Force has announced another test of the X-51 Waverider coming up on March 22nd. This will be the latest in only a handful of tests of a new supersonic combustion ramjet engine, also known as a scramjet. The test should involve flying at Mach 6 for about four minutes. Hopefully we’ll have see some exciting results from that test flight in a week or so.
High-Speed Cooking
I suspect demonstrating fluid mechanics was not what this cookbook had in mind when they filmed creamer poured into coffee at 2000 fps, but there’s some awesome droplet breakup, crowning, roiling turbulent mixing, and even some deformed Worthington jets here. It’s a reminder that, even though we may not notice it, fluid dynamics are all around.
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 as sonoluminescence. The whole event takes less than 300 microseconds. The light emitted suggests that temperatures inside the bubble reach 5,000 degrees Kelvin, around the temperature of the surface of the sun. #
The GE Show
[original media no longer available]
While this video is not strictly about fluid dynamics, there are some pretty cool high-speed fluids moments in it. Watch the reaction of the gelatins as objects hit them and observe the deformation of the water balloons as they strike. (via JetForMe)
Colorful Computational Combustion
Many fluid dynamics problems are so complicated that they require supercomputers to calculate the mathematical and physical details. This image shows a computer simulation of a cold ethylene jet combusting in hot air. Different colors indicate different combustion by-products. Researchers use simulations like this one to investigate ideal flames that improve efficiency in applications like cars or jet engines. #
