In this flow visualization, wingtip vortices from an aircraft have been simulated using an apparatus with a couple of flaps that snap together like a book closing. Dye is pooled on the “ground” below the flaps and gets entrained by the vortices and lit up using laser light. The red vortices are the primary vortex generated by the aircraft wingtips and the green ones are secondary vortices generated by interaction with the ground. The lower half of the picture is a reflection off the ground. This photo was part of the 2009 Gallery of Fluid Motion. #
Category: Research
Human-Powered Ornithopter
A team at the University of Toronto has flown the world’s first human-powered ornithopter, an aircraft that flies by flapping its wings like a bird. The concept dates back all the way to Da Vinci in the 15th century. Part of why it’s taken centuries to realize the dream is that bird flight is much more complicated than simply flapping up and down. Flapping a wing up and down will produce lift equally upward and downward. In order to create usable lift and thrust, it’s necessary to change the angle of attack during each stroke by twisting the wing while flapping. Watch the U of T craft carefully, and you can see this happening. #
Breaking up in Crossflow
This video shows some instabilities that occur when a liquid jet impinges on a flowing cross stream. Note how the jet breaks down into droplets in a fashion similar to the Plateau-Rayleigh instability but the broken tip remains stable for some time thereafter. #
Sailing Faster than the Wind
Is it possible to create a vehicle that uses the wind to move itself directly downwind faster than the wind does? Strangely enough, it is. The concept has been the subject of debate for years, but one team has confirmed the physics by building a vehicle that uses wind but can travel 2.8x faster than the wind does. See their article on Wired. #
Flying Fish Aerodynamics
New research using wind tunnel measurements of (dead) flying fish is giving new insight into how these fish are able to fly over the waves. Lift and drag data indicates that flying fish have a gliding ability comparable to soaring birds like hawks! #
Whipping Instabilities
When jets of liquid are introduced into an electrified medium in a process known as electrospinning, they can exhibit behavior known as whipping instabilities.
The Bouncing Jet
Under some circumstances, a thin stream of a Newtonian fluid impacting a deep pool of the same fluid can produce a bouncing jet. The effect is observed in common liquids like canola oil and can be replicated at home. Be sure to check the research page for a video of the effect. #
How to Grow Straight Icicles
New research suggests that icicles grow straighter when exposed to moving air while exposure to still air can cause icicles to sprout at their tips. To grow icicles, the researchers built a refrigerated box that dripped water from the top while the growing icicle rotated. Understanding ice growth is important for flight aerodynamics and icing on airplane wings. For videos and more on icicle growth, see the article at Wired Science. #
Happy Anniversary, Enterprise!
Wind tunnels are great, but there’s nothing like a flight test to learn about the aerodynamics of a new vehicle. Today in 1977, the space shuttle prototype Enterprise flew on its own for the first time. Enterprise was built purely to test the shuttle’s aerodynamic behavior during gliding and landing. Check out this video of one of Enterprise’s gliding and landing tests.
