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Information about Vortices

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NSSL vehicles on Project VORTEX, equipped with surface measurement equipment.
Verification of the Origins of Rotation in Tornadoes Experiment or VORTEX, is a field project that seeks to understand how a tornado is produced by deploying around 18 vehicles that are equipped with customized instruments used to measure and analyze the weather around a tornado. The project has also stated that it is interested in why some supercells produce tornadoes while others do not. The original project took place in 1994 and 1995, and another project was run in 1999.

The movie Twister was at least partially inspired by the VORTEX project.

A second VORTEX project, named VORTEX2 is being planned for 2009-10.

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Vortex created by the passage of an aircraft wing, revealed by coloured smoke
A vortex (pl. vortices) is a spinning, often turbulent, flow (or any spiral motion) with closed streamlines. The shape of media or mass swirling rapidly around a center forms a vortex. It flows in a circular motion.

Dynamics

A vortex can be any circular or rotary flow that possesses vorticity. Vorticity is a mathematical concept used in fluid dynamics. It can be related to the amount of "circulation" or "rotation" in a fluid. In fluid dynamics, vorticity is the circulation per unit area at a point in the flow field. It is a vector quantity, whose direction is (roughly speaking) along the axis of the swirl. Also in fluid dynamics, the movement of a fluid can be said to be vortical if the fluid moves around in a circle, or in a helix, or if it tends to spin around some axis. Such motion can also be called solenoidal. In the atmospheric sciences, vorticity is a property that characterizes large-scale rotation of air masses. Since the atmospheric circulation is nearly horizontal, the (3 dimensional) vorticity is nearly vertical, and it is common to use the vertical component as a scalar vorticity. Mathematically, it is defined as,
:
where is the ''fluid velocity''.

Two types of vortex

In fluid mechanics, a distinction is often made between two limiting vortex cases. One is called the free (irrotational) vortex, and the other is the forced (rotational) vortex. These are considered as below:
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Two autumn leaves in a counter-clockwise vortex (reference position).
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Two autumn leaves in a rotational vortex rotate with the counter-clockwise flow.

Free (irrotational) vortex

When fluid is drawn down a plug-hole, one can observe the phenomenon of a free vortex. The tangential velocity v varies inversely as the distance r from the center of rotation, so the angular momentum, rv, is constant; the vorticity is zero everywhere (except for a singularity at the center-line) and the circulation about a contour containing r=0 has the same value everywhere. The free surface (if present) dips sharply (as ) as the center line is approached.

The tangential velocity is given by:

                 (2.1)


where Γ is the circulation and r is the radial distance from the center of the vortex.

In non-technical terms the circular streamlines toward the center can sweep out a given angle faster than the outer streamlines. The speed along the circular path of flow is held constant or decreases as you move out from the center. At the same time the inner streamlines have a shorter distance to travel to complete a ring. If you were running a race on a circular track would you rather be on the inside or outside, assuming the goal was to complete a circle? Imagine a leaf floating in a free vortex. The leaf's tip points to the center and the blade straddles multiple streamlines. The outer flow is slow in terms of angle traversed and it exerts a backwards tug on the base of the leaf while the faster inner flow pulls the tip forwards. The drag force opposes rotation of the leaf as it moves around the circle.

Forced (rotational) vortex

In a forced vortex the fluid essentially rotates as a solid body (there is no shear). The motion can be realised by placing a dish of fluid on a turntable rotating at T radians/sec; the fluid has vorticity of 2 T everywhere, and the free surface (if present) is a parabola.

The tangential velocity is given by:

                 (2.2)


where ω is the angular velocity and r is the radial distance from the center of the vortex.

Observations

A vortex can be seen in the spiraling motion of air or liquid around a center of rotation. Circular current of water of conflicting tides form vortex shapes. Turbulent flow makes many vortices. A good example of a vortex is the atmospheric phenomenon of a whirlwind or a tornado or dust devil. This whirling air mass mostly takes the form of a helix, column, or spiral. Tornadoes develop from severe thunderstorms, usually spawned from squall lines and supercell thunderstorms, though they sometimes happen as a result of a hurricane.

A mesovortex is on the scale of a few miles (smaller than a hurricane but larger than a tornado). [2] On a much smaller scale, a vortex is usually formed as water goes down a drain, as in a sink or a toilet. This occurs in water as the revolving mass forms a whirlpool. This whirlpool is caused by water flowing out of a small opening in the bottom of a basin or reservoir. This swirling flow structure within a region of fluid flow opens downward from the water surface.

Instances

  • In the hydrodynamic interpretation of the behaviour of electromagnetic fields, the acceleration of electric fluid in a particular direction creates a positive vortex of magnetic fluid. This in turn creates around itself a corresponding negative vortex of electric fluid.
  • Smoke ring : A ring of smoke in the air.
  • Lift-induced drag of a wing on an aircraft.
  • The primary cause of drag in the sail of a sloop.
  • Whirlpool : a swirling body of water produced by ocean tides or by a hole underneath the vortex, where water drains out, as in a bathtub. A large, powerful whirlpool is known as a maelstrom. In popular imagination, but only rarely in reality, can they have the dangerous effect of destroying boats.
  • Tornado : a violent windstorm characterized by a twisting, funnel-shaped cloud. A less violent version of a tornado, over water, is called a waterspout.
  • Hurricane : a much larger, swirling body of clouds produced by evaporating warm ocean water and influenced by the Earth's rotation. Similar, but far greater, vortices are also seen on other planets, such as the permanent Great Red Spot on Jupiter and the intermittent Great Dark Spot on Neptune.
  • Polar vortex : a persistent, large-scale cyclone centered near the Earth's poles, in the middle and upper troposphere and the stratosphere.
  • Sunspot : dark region on the Sun's surface (photosphere) marked by a lower temperature than its surroundings, and intense magnetic activity.
  • The accretion disk of a black hole or other massive gravitational source.
  • Spiral galaxy : a type of galaxy in the Hubble sequence which is characterized by a thin, rotating disk. Earth's galaxy, the Milky Way is of this type.

See also

References and further reading

  • "Weather Glossary"' The Weather Channel Interactive, Inc.. 2004.
  • "Glossary and Abbreviations". Risk Prediction Initiative. The Bermuda Biological Station for Research, Inc.. St. George's, Bermuda. 2004.
  • Loper, David E., "An analysis of confined magnetohydrodynamic vortex flows". Case Institute of Technology. Washington, National Aeronautics and Space Administration]; for sale by the Clearinghouse for Federal Scientific and Technical Information, Springfield, Va. 1966. (NASA contractor report NASA CR-646) LCCN 67060315
  • Batchelor, G. K. (1967), An Introduction to Fluid Dynamics, Cambridge Univ. Press, Ch. 7 et seq

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tornado is a violently rotating column of air which is in contact with both a cumulonimbus cloud or, in rare cases, a cumulus cloud base and the surface of the earth. Tornadoes come in many sizes but are typically in the form of a visible condensation funnel, whose narrow end
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weather is the set of all extant phenomena in a given atmosphere at a given time. The term usually refers to the activity of these phenomena over short periods (hours or days), as opposed to the term climate, which refers to the average atmospheric conditions over longer periods of
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supercell is a severe thunderstorm with a deep, persistently rotating updraft (a mesocyclone).[1] Supercell thunderstorms are the largest, most severe class of thunderstorms.
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Twister is a 1996 disaster film starring Helen Hunt and Bill Paxton as storm chasers researching tornadoes. It was directed by Jan de Bont.
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This article is about rotation as a movement of a physical body. For other uses, see Rotation (disambiguation).
A rotation is a movement of an object in a circular motion.
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turbulence or turbulent flow is a flow regime characterized by chaotic, stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time.
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spiral is a curve which emanates from a central point, getting progressively farther away as it revolves around the point.

Spiral or helix

A "spiral" and a "helix" are two terms that are easily confused, but represent different objects.
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Streamlines are a family of curves that are instantaneously tangent to the velocity vector of the flow. This means that if a point is picked then at that point the flow moves in a certain direction.
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Vorticity is a mathematical concept used in fluid dynamics. It can be related to the amount of "circulation" or "rotation" (or more strictly, the local angular rate of rotation) in a fluid.
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Fluid dynamics is the sub-discipline of fluid mechanics dealing with fluids (liquids and gases) in motion. It has several subdisciplines itself, including aerodynamics (the study of gases in motion) and hydrodynamics (the study of liquids in motion).
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spatial vector, or simply vector, is a concept characterized by a magnitude and a direction. A vector can be thought of as an arrow in Euclidean space, drawn from an initial point A pointing to a terminal point B.
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Vortical means pertaining to a vortex or to vortices. In fluid dynamics, the movement of a fluid can be said to be vortical if the fluid moves around in a circle, or in a helix, or if it tends to spin around some axis. Such motion can also be called solenoidal.
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In vector calculus a solenoidal vector field is a vector field v with divergence zero:



This condition is satisfied whenever v has a vector potential, because if



then


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In fluid dynamics, circulation is the line integral around a closed curve of the fluid velocity. Circulation is normally denoted . If is the fluid velocity and is a unit vector along the closed curve :


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angular velocity is a vector quantity (more precisely, a pseudovector) which specifies the angular speed at which an object is rotating along with the direction in which it is rotating.
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Air or Earth's atmosphere is a layer of gases surrounding the planet Earth.

Air may also refer to:
  • Air (1977 video game), an air combat based mainframe computer game
  • Air (band), a French electronic music duo

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Liquid is one of the four principal states of matter. A liquid is a fluid that can freely form a distinct surface at the boundaries of its bulk material.

Characteristics

A liquid's shape is determined by, not confined to, the container it fills.
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This article is about rotation as a movement of a physical body. For other uses, see Rotation (disambiguation).
A rotation is a movement of an object in a circular motion.
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Tides are the cyclic rising and falling of Earth's ocean surface caused by the tidal forces of the Moon and the Sun acting on the oceans. More generally, tidal phenomena can occur in any object that is subjected to a gravitational field that varies in time and space, such as the
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turbulence or turbulent flow is a flow regime characterized by chaotic, stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time.
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Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity. It contains roughly (by molar content/volume) 78% nitrogen, 20.95% oxygen, 0.93% argon, 0.
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Whirlwind may refer to:
  • An atmospheric phenomenon, see whirlwind (atmospheric phenomenon)
  • Several aircraft, see Westland Whirlwind
  • MIT's pioneering Whirlwind computer
  • Jimmy White, a famous British Snooker player, is nicknamed The Whirlwind

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tornado is a violently rotating column of air which is in contact with both a cumulonimbus cloud or, in rare cases, a cumulus cloud base and the surface of the earth. Tornadoes come in many sizes but are typically in the form of a visible condensation funnel, whose narrow end
..... Click the link for more information.
dust devil is a rotating updraft, ranging from small (half a meter wide and a few meters tall) to large (over 10 meters wide and over 1000 meters tall). In the southwestern United States, dust devils can be known as dancing devils.
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should be added to this article, to conform with Wikipedia's Manual of Style.
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A helix (pl: helices), from the Greek word έλικας/έλιξ
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A column in architecture and structural engineering is a vertical structural element that transmits, through compression, the weight of the structure above to other structural elements below.
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spiral is a curve which emanates from a central point, getting progressively farther away as it revolves around the point.

Spiral or helix

A "spiral" and a "helix" are two terms that are easily confused, but represent different objects.
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A squall line is a line of severe thunderstorms that can form along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front. It contains heavy precipitation, hail, frequent lightning, strong straight line winds, and possibly tornadoes and
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supercell is a severe thunderstorm with a deep, persistently rotating updraft (a mesocyclone).[1] Supercell thunderstorms are the largest, most severe class of thunderstorms.
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tropical cyclone is a meteorological term for a storm system characterized by a low pressure system center and thunderstorms that produces strong wind and flooding rain. A tropical cyclone feeds on the heat released when moist air rises and the water vapor it contains condenses.
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