Computational fluid dynamics (CFD) sometimes gets a bad rep as “colorful fluid dynamics”, but as computers get faster and faster, more complicated and physically accurate simulations are possible. Shown here are simulations of vortex rings and wingtip vortices in stunningly gorgeous detail. Understanding the evolution of these vortices from a fundamental level helps fluid mechanicians design better methods of controlling them. As mentioned in the video, wingtip vortices are a particularly hazardous everyday example; the time it takes for one plane’s wingtip vortices to disperse determines how quickly the next airplane can take-off or land on that same runway. Being able to break down these vortices faster would allow more frequent use of existing facilities.
Tag: fluid dynamics
Solar Fluid Dynamics
The sun is a wild place fluid dynamically. The surface is riddled with convection cells the size of the Earth, and prominences of plasma (ionized gas) erupt from the surface following the sun’s magnetic field lines. Violent, but beautiful. #
Underwater Explosions
As powerful as explosions can be above ground, they are even more dangerous underwater. Since water, unlike air, is incompressible, the pressure wave at the front of an underwater explosion is not damped to the extent it would be in air. A high-pressure, high-temperature bubble of gas also forms in the explosion, and, as with cavitation, if the bubble collapses near metal, the damage can be extensive. (via Gizmodo)
Smoke Visualization on an F-16
Flow around an F-16XL Scamp model is visualized using smoke illuminated by laser sheets. Lasers are common equipment in fluids laboratories; they’re useful for flow visualization and for many velocimetry techniques.
Droplet Impact on Superhydrophobic Surfaces
High-speed video of water droplets impacting on superhydrophobic surfaces demonstrates the impressive elasticity and surface tension of the droplets. Impacts vibrate and reflect through the droplet, but only a drop from the largest height actually causes breakup.
Wind Tunnel Testing
This photo shows a prototype of the X-48C blended wing body aircraft being tested in NASA Langley’s 12-Foot Low-Speed Tunnel. Blended wing bodies have many advantages over conventional tube-and-wing designs: the entire surface of the craft can generate lift; the usable cargo/passenger area of the craft is increased; and, structurally, the craft is easier to manufacture. Flight tests of a remote-controlled version of the craft have also taken place.
Hawaiian Fissures
[original media no longer available]
New fissures opened on Mount Kilauea in Hawaii earlier this month, resulting in some fountain-like eruptions of lava. This molten rock is a non-Newtonian fluid with shear-thinning and thixotropic properties. This is what allows the lava to flow long distances before it cools and solidifies. (via jpshoer)
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.
Propeller Cavitation
Gas bubbles can form in a flowing liquid in areas where the pressure drops below its vapor pressure. This process, called cavitation, is a major problem for engineers because the collapse of the bubbles upon entering a high pressure area can damage metal surfaces. Shown here is cavitation on a fully submerged boat propeller.
Aerodynamics with Bill Nye and Samuel L. Jackson
Bill Nye, Samuel Jackson, golf balls, Reynolds number, dimples, and boundary layers. It doesn’t get much better than this. – Khristopher O (submitter)
It definitely beats Jackson’s other foray into aerodynamics! The dimples on a golf ball cause turbulent boundary layers, which actually decrease drag on the ball and make it fly farther. Why bluff bodies experience a reduction in drag as speed (and thus Reynolds number) increases was a matter of great confusion for fluid mechanicians early in the twentieth century, but it’s not too hard to see why it happens with some flow visualization.
On the top sphere, the laminar boundary layer separates from the sphere just past its shoulder. This results in a pressure loss on the backside of the sphere and, thus, an increase in drag. On the bottom sphere, a trip-wire placed just before the shoulder causes a turbulent boundary layer, which separates from the sphere farther along the backside. This late separation results in a thinner wake and a smaller pressure loss behind the sphere, thereby reducing the overall drag when compared to the laminar case. (Photo credit: An Album of Fluid Motion)
