Wingtip vortices form on airplanes due to the finite length of their wings. In general, lift on the wings results from low-pressure, high-velocity air moving over the top of the wing and high-pressure, low-velocity air moving below the wing. Near the wingtips, the high-pressure air is able to slip around the edge to the top of the wing, generating a vortex that then trails behind the airplane. The same thing is occurring in the video above, except the edges of the wing’s control surfaces are serving as the tip of the wing. Similar vortices also exist at the wingtips, but they are not made visible by condensation as the aileron vortices are.
Tag: wingtip vortices
Wingtip Vortices in Ground Effect
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If you’ve ever watched airplane contrails fade, you’ve probably observed the Crow instability, which causes the trailing wingtip vortices of the plane to interact and distort. The same effect is explored in the video above with the addition of ground effect. The first clip shows a pair of counter-rotating vortices from the side, showing a periodic pattern of thickening and thinning along the vortices. The second clip shows cross-sectional slices of the vortices at a thin and a thick point.
Flow Around a Delta Wing
Smoke visualization in a wind tunnel shows the vortices wrapping around and trailing behind a delta wing. As with more commonly seen rectangular or swept wings, the vortices that form around delta wings affect lift, drag, and control of an aircraft. They can also be hazardous to aircraft nearby. Note that, although delta wings are often seen on supersonic aircraft, this visualization only applies at subsonic speeds. The flow field changes drastically above the speed of sound.
Aircraft Contrails
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Under the right atmospheric conditions, condensation can form, even at low speeds, as moist air is accelerated over airplane wings. This acceleration causes a local drop in pressure and temperature, which can cause water vapor in the air to condense. The condensation can sometimes get pulled into the wingtip vortices shed off of the wings, tail, and ailerons of an aircraft, as in the video above, making the aerodynamics of the airplane visible to the naked eye.
Starting Vortices
Whenever a wing stops or starts in a fluid, it produces a vortex. This 2D numerical simulation shows an airfoil repeatedly starting and stopping, shedding a vortex each time. Note how the line of vortices drifts downward in the wake; this is an indication of downwash. (submitted by jessecaps)
Propeller Cavitation
Cavitation occurs in moving liquids when the local pressure–in this case, at the tip of the propeller–drops below the vapor pressure. The fast-moving fluid transitions to a gas phase, creating a tip vortex of water vapor even though the propeller is completely submerged.
Ground Effect Vehicles
Ground effect vehicles (a.k.a. wing-in-ground-effect vehicles) rely on their proximity to a flat surface to inhibit the wingtip vortices that create lift-induced drag. This effectively increases the lifting capabilities of the vehicle in comparison to regular flight, but only so long as the vehicle remains close enough to the ground. This video features many model gliders that rely on ground effect.
Airplane Vortex Wake
The wingtip vortices in the wake of a commercial airliner distort the clouds as the plane descends. Wingtip vortices form as a result of high pressure air from the underside of the wing accelerating around the wingtips to reach the low pressure on top of the wing. They can be hazardous to other (lighter) aircraft. They also contribute to downwash that decreases the effective lift of a wing. Geese use the same mechanism to their advantage when flying in a V-formation, and some snakes use it to glide.
The Ekranoplan
The ekranoplan, the monster of the Caspian Sea, was a Soviet-era aircraft nearly 74 meters in length and weighing 380,000 kgs fully loaded. (In contrast, the C-17 is 53 m long and weighs 265,350 kg fully loaded.) This enormous craft relied on ground effect to stay aloft, where it was capable of 297 knots. Flying close to the ground or water increases the possible lift on wings through a “cushioning effect” that increases pressure on the lower wing surface and by disrupting the formation of wingtip vortices which typically reduce lift through downwash.
Computational Vortex Rings
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.
