Changes

* Two or more vortices that are approximately parallel and circulating in the same direction will quickly merge to form a single vortex.  The [[Circulation (fluid dynamics)|circulation]] of the merged vortex will equal the sum of the [[Circulation (fluid dynamics)|circulations]] of the constituent vortices.  For example, a sheet of small vortices flows from the trailing edge of the wing or propeller of an airplane when the wing is developing [[Lift (force)|lift]] or the propeller is developing [[thrust]].  In less than one wing [[Chord (aircraft)|chord]] downstream of the trailing edge of the wing these small vortices merge to form a single vortex.  If viewed from the tail of the airplane, looking forward in the direction of flight, there is one [[Wingtip vortices|wingtip vortex]] trailing from the left-hand wing and circulating clockwise, and another wingtip vortex trailing from the right-hand wing and circulating anti-clockwise.  The result is a region of downwash behind the wing, between the pair of [[wingtip vortices]].  These two [[wingtip vortices]] do not merge because they are circulating in opposite directions.

* Two or more vortices that are approximately parallel and circulating in the same direction will quickly merge to form a single vortex.  The [[Circulation (fluid dynamics)|circulation]] of the merged vortex will equal the sum of the [[Circulation (fluid dynamics)|circulations]] of the constituent vortices.  For example, a sheet of small vortices flows from the trailing edge of the wing or propeller of an airplane when the wing is developing [[Lift (force)|lift]] or the propeller is developing [[thrust]].  In less than one wing [[Chord (aircraft)|chord]] downstream of the trailing edge of the wing these small vortices merge to form a single vortex.  If viewed from the tail of the airplane, looking forward in the direction of flight, there is one [[Wingtip vortices|wingtip vortex]] trailing from the left-hand wing and circulating clockwise, and another wingtip vortex trailing from the right-hand wing and circulating anti-clockwise.  The result is a region of downwash behind the wing, between the pair of [[wingtip vortices]].  These two [[wingtip vortices]] do not merge because they are circulating in opposite directions.

* Vortices contain a lot of energy in the circular motion of the fluid.  In an ideal fluid this energy can never be dissipated and the vortex would persist forever.  However, real fluids exhibit [[viscosity]] and this dissipates energy very slowly from the core of the vortex.  (See [[Rankine vortex]]).  It is only through dissipation of a vortex due to viscosity that a vortex line can end in the fluid, rather than at the boundary of the fluid.  For example, the [[wingtip vortices]] from an airplane dissipate slowly and linger in the atmosphere long after the airplane has passed.  This is a hazard to other aircraft and is known as [[wake turbulence]].[http://en.wikipedia.org/wiki/Vortex]

* Vortices contain a lot of energy in the circular motion of the fluid.  In an ideal fluid this energy can never be dissipated and the vortex would persist forever.  However, real fluids exhibit [[viscosity]] and this dissipates energy very slowly from the core of the vortex.  (See [[Rankine vortex]]).  It is only through dissipation of a vortex due to viscosity that a vortex line can end in the fluid, rather than at the boundary of the fluid.  For example, the [[wingtip vortices]] from an airplane dissipate slowly and linger in the atmosphere long after the airplane has passed.  This is a hazard to other aircraft and is known as [[wake turbulence]].[https://en.wikipedia.org/wiki/Vortex]

[[Category: General Reference]]

[[Category: General Reference]]

[[Category: Physics]]

[[Category: Physics]]