Hvirvel
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Hvirvel i en dam.
En hvirvel (la. vortex), er i fluidmekanikken en roterende bevægelse i en fluid. Det kan f.eks. iagttages, når vand strømmer ud af bunden i et badekar.
Alle spiralbevægelser med lukkede strømlinjer er hvirvelstrømme. Bevægelse af en væske, der hvirvler hurtigt omkring et center, kaldes en vortex. Hastigheder og rotationshastighed af væskens hastighed er størst nær centrum og aftager gradvist væk fra centrum.
Hvirvler kan være en såkaldt fri vortex, hvor den individuelle hvirvel opretholder energi i form af en strømkilde eller et fald i vortexcentrum, som derefter danner en logaritmisk strømformular.
Et kaotisk system af hvirvler kaldes for turbulent strømning.
Se også
Referencer
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Airplane vortex edit.jpg
Wake Vortex Study at Wallops Island
The air flow from the wing of this agricultural plane is made visible by a technique that uses colored smoke rising from the ground. The swirl at the wingtip traces the aircraft's wake vortex, which exerts a powerful influence on the flow field behind the plane. Because of wake vortex, the Federal Aviation Administration (FAA) requires aircraft to maintain set distances behind each other when they land. A joint NASA-FAA program aimed at boosting airport capacity, however, is aimed at determining conditions under which planes may fly closer together. NASA researchers are studying wake vortex with a variety of tools, from supercomputers, to wind tunnels, to actual flight tests in research aircraft. Their goal is to fully understand the phenomenon, then use that knowledge to create an automated system that could predict changing wake vortex conditions at airports. Pilots already know, for example, that they have to worry less about wake vortex in rough weather because windy conditions cause them to dissipate more rapidly.
Wake Vortex Study at Wallops Island
The air flow from the wing of this agricultural plane is made visible by a technique that uses colored smoke rising from the ground. The swirl at the wingtip traces the aircraft's wake vortex, which exerts a powerful influence on the flow field behind the plane. Because of wake vortex, the Federal Aviation Administration (FAA) requires aircraft to maintain set distances behind each other when they land. A joint NASA-FAA program aimed at boosting airport capacity, however, is aimed at determining conditions under which planes may fly closer together. NASA researchers are studying wake vortex with a variety of tools, from supercomputers, to wind tunnels, to actual flight tests in research aircraft. Their goal is to fully understand the phenomenon, then use that knowledge to create an automated system that could predict changing wake vortex conditions at airports. Pilots already know, for example, that they have to worry less about wake vortex in rough weather because windy conditions cause them to dissipate more rapidly.