(redirected from vortices)
Also found in: Dictionary, Thesaurus, Medical.


(vôr`tĕks), mass of fluid in whirling or rotary motion. To simplify the analysis, vortex motion usually describes motions in a frictionless fluid. In such cases the absence of friction would make it impossible to create or to destroy vortex motion. Motion in such a fluid would be a permanent flow pattern; the velocity of the fluid element instantaneously passing through a given point in space would be constant in time. Lines drawn so that their direction is that of the axis of rotation of the fluid are called vortex lines, and if these lines close on themselves they are called vortex rings. Hermann von Helmholtz was probably the first to investigate the properties of vortex motion; Lord Kelvin developed a theory of the material atom as a vortex ring; and J. C. Maxwell worked out a theory of electromagnetism, assuming that every magnetic tube of force was a vortex with an axis of rotation coinciding with the direction of the force. Many properties have been mathematically proved for the perfect frictionless fluid. In practice, however, their full realization is impossible because no frictionless fluid exists. To maintain a vortex motion a continuous energy supply to overcome friction is needed. A smoke ring is a familiar example of a typical vortex motion in which the medium is air. In this case the rings are stable for a short time because of the comparatively slight friction in air. An illustration of vortex motion in a liquid medium is the small whirlpool formed by water as it drains from a wash basin. In nature, illustrations of vortical motion on a larger scale are seen in waterspouts, whirlpools, and tornadoes. Investigations of sunspots reveal enormous vortices in the gases surrounding them. The principles of vortex motion are applied in aerodynamics, e.g., to explain the movement of air behind the trailing edge of a wing.


In common usage, a fluid motion dominated by rotation about an isolated curved line in space, as in a tornado, a whirlpool, a hurricane, or a similar natural phenomenon. The importance of vortices is due to two characteristics: general fluid flows can be represented by a superposition of vortices; and vortices, once created, have a persistence that increases as the effects of viscosity are reduced. The aerodynamic lift forces and most other contributors to the forces and moments on aircraft and other bodies moving through fluids do not exist in the absence of vortices. See Aerodynamic force

The strength of rotation is measured by a vector called the vorticity, &ohgr;, defined as the curl of the velocity vector. A region of flow devoid of vorticity is known as irrotational. The spatial distribution of the vorticity vector provides a precise characterization of the rotation effects in fluids, and the nature of what subjectively and popularly would be called a vortex. See Laplace's irrotational motion

The vorticity vector field can be constructed by measuring the instantaneous angular velocity of small masses of fluid. The vorticity vector is twice the local angular velocity vector. Starting at any arbitrary point in the fluid, a line, called a vortex line, can be drawn everywhere parallel to the vorticity vector.

A bundle of vortex lines defines a tubular region of space, called a vortex tube, with a boundary surface that no vortex line crosses.

Two simple rules follow from the definitions: (1) a vortex tube must either close on itself or end on a boundary of the fluid (including extending to “infinity” if the fluid is imagined to fill all space); and (2) at every cross section of a given vortex tube, the area integral of the normal vorticity has the same value at any given instant. The area integral is, by Stokes' theorem, equal to a line integral around the periphery of the tube, namely, the line integral of the velocity component parallel to the direction of the line integral. This quantity is also known as the circulation around the line, so at an instant of time a vortex tube has a unique value of the circulation applying to all cross sections (see illustration).

Vortex tube; &ohgr; is the vorticityenlarge picture
Vortex tube; &ohgr; is the vorticity

Vortex lines confined to a layer rather than a tube describe fluid motion of a different character. This is most easily visualized when the direction of the vorticity does not vary, so all of the vortex lines are straight and parallel. Assuming the vorticity has zero magnitude outside the layer, this vortex layer represents a flow with a different speed and direction on either side of the layer. Such a change in speed occurs at the edge of wakes produced by wind passing over an obstacle. Reducing the thickness of this layer of vorticity to zero leads to an idealization known as a vortex sheet, a surface in space across which there is a finite jump in velocity tangent to the surface. Vortex sheets have a tendency to roll up, because of self-induction.


(fluid mechanics)
Any flow possessing vorticity; for example, an eddy, whirlpool, or other rotary motion.
A flow with closed streamlines, such as a free vortex or line vortex.
(solid-state physics)


Vortex streamline flow.
i. In meteorology, any rotary flow in the atmosphere.
ii. As used in aerodynamics, circular patterns of air created by the movement of an airfoil through the air when generating lift. As an airfoil moves through the atmosphere in sustained flight, an area of low pressure is created above it. The air flowing from the high-pressure area to the low-pressure area around and about the tips of the airfoil tends to roll up into two rapidly rotating vortices, cylindrical in shape. These vortices are the most predominant parts of aircraft wake turbulence, and their rotational force is dependent upon the wing loading, gross weight, and speed of the generating aircraft. The most important factor is weight. The greatest vortex strength occurs when the generating aircraft is heavy, clean, and slow. This situation occurs soon after a takeoff. Peak vortex tangential speeds of 300 ft/s have been recorded. A vortex can induce roll and, in rare cases, cause structural damage to the aircraft that is following the aircraft generating the vortex. The vortices from medium and heavy aircraft can be extremely hazardous to smaller aircraft, especially during takeoff and landing behind the larger aircraft.


a whirling mass or rotary motion in a liquid, gas, flame, etc., such as the spiralling movement of water around a whirlpool
References in periodicals archive ?
When the researchers analyzed the shots, the results were unambiguous: The wing had generated knotted vortices.
From the obtained pictures, it is seen that on the vertical plane, the vortices observed continue to expand and in the front of the vortices, new vortex seems to occur.
In general, the axes of vortices 1 and 2 do not intersect, and the shortest normal distance between them is 2d.
This unpredictable nature of the Venus polar vortices make them different from polar vortices found on other planets, like Earth or Saturn, which are much more stable and predictable.
i] < [alpha]), it will remain in the contact layer and vortices may be diffused in the next time steps.
The airline industry knows that most of the time the wake vortices are not present in the path of the trailing airplane because they either drift to the side with a cross wind, or sink below the path of the next aircraft.
The new findings suggest that leading-edge vortices playa crucial role in bird flight as well.
Hill examined how such vortices behave when they encounter wind shear, a natural phenomenon in which adjacent layers of air move at different speeds or in different directions.
Our results point to several experimental and theoretical situations where such structures may be relevant, ranging from defects in liquid crystals and vortices in superfluid helium to the structure-forming role of cosmic strings in the early universe," Niemi and Faddeev say.
However, the space-width alternation phenomenon familiar from linear chromeless phase-edge lithography does cause small positional errors for vortex vias, and each of the four vortices in the repeating pattern behaves somewhat differently through focus, potentially limiting the common process window.
It's lovely, you sit in a chair and watch the vortices," says Ellington.
Precise knowledge of the location and motion of the wake vortices could give air traffic controllers the flexibility to safely shorten the arrival and departure spacing intervals when conditions permit, potentially reducing passenger delays, taxiway queues, and aircraft fuel consumption.