Crow Instability
Encyclopedia
In aerodynamics
, the Crow Instability is an inviscid
line-vortex instability, named after its discoverer S. C. Crow.
The Crow instability is most commonly observed in the skies behind large aircraft, when the wingtip vortices
interact with contrail
s from the engines, producing visible distortions in the shape of the contrail.
Aerodynamics
Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...
, the Crow Instability is an inviscid
Inviscid flow
In fluid dynamics there are problems that are easily solved by using the simplifying assumption of an ideal fluid that has no viscosity. The flow of a fluid that is assumed to have no viscosity is called inviscid flow....
line-vortex instability, named after its discoverer S. C. Crow.
The Crow instability is most commonly observed in the skies behind large aircraft, when the wingtip vortices
Wingtip vortices
Wingtip vortices are tubes of circulating air that are left behind a wing as it generates lift. One wingtip vortex trails from the tip of each wing. The cores of vortices spin at very high speed and are regions of very low pressure...
interact with contrail
Contrail
Contrails or vapour trails are artificial clouds that are the visible trails of condensed water vapour made by the exhaust of aircraft engines...
s from the engines, producing visible distortions in the shape of the contrail.
Instability development
The Crow Instability is a vortex pair instability, and typically goes through several stages:- A pair of counter rotating vortices act upon each other to amplify small sinusoidal distortions in their vortex shapes (Normally created by some initial disturbance in the system).
- The waves develop into either symmetric or anti-symmetric modes, depending on the nature of the initial disturbance.
- These distortions grow, both through interaction from one vortex on another, and also 'Self Induction' of a vortex with itself. This leads to an exponential growth in the vortex wave amplitude.
- The vortex amplitudes reach a critical value and reconnect, forming a chain of vortex ringVortex ringA vortex ring, also called a toroidal vortex, is a region of rotating fluid moving through the same or different fluid where the flow pattern takes on a toroidal shape. The movement of the fluid is about the poloidal or circular axis of the doughnut, in a twisting vortex motion...
s.