Vortex

As a vortex, or vortex is known in fluid mechanics circular flows of a fluid. In meteorology and in the vortex aerodynamics play an important role.

Formation

Many vortices are formed as a result of velocity gradients within the fluid. That is, a part of the liquid flows significantly faster than the rest, this is for example the case

• When water flows out of a pool in a drain pipe to form vortex
• When the body of a laminar flow afford frictional resistance. This is the passing air in aircraft. In ships it is the displaced water.
• When two liquid quantities at different speeds collide

In vertebrae energy is dissipated. That is, the fluid energy is extracted and converted into heat energy. The flowing fluid is thus heated by the eddy while deprived him of kinetic energy. The more turbulent, the vortex in a fluid, the more energy is dissipated. It does not matter for the principle, if a steady flow, an unsteady flow or turbulent flow is present. Vortices can thereby stay in one place (stationary), as at the top of an airfoil at a low Reynolds number, it can come off periodically, or show a seemingly chaotic behavior. The last case is an indicator of a turbulent flow

Behind a cylinder around which flow occurs at not too great a flow Reynolds number of the Karman vortex street. Here, the left - and right - rotating vortices dissolve in a characteristic pattern alternately from. At higher speeds, more vortices occur, so that the flow resistance increases sharply. The size of the vortex and the times they are replaced more and more varied. This is the transition to turbulence. When fully developed turbulent eddies are present on all scales.

Another mechanism that gives rise to vertebrae, are inertial forces in fluids, which rotate as a whole. The Coriolis effect deflects currents within the fluid around. This is the reason that low-pressure areas form the center of a vortex. The Polar vortex and the jet streams are also vortices caused by inertial forces.

At the beginning of the theoretical description of the vortex for incompressible fluids is the rotation field

Corresponding to the vortex field. is also referred to as vorticity or vortex density.

Forced vortex

A forced vortex is a rotationally -prone vertebrae.

An extreme type of such a flow is the vortex solid, if after a long start-up time according to a liquid turns such as in a vessel on a turntable with constant angular velocity of a rigid body.

Potential vortex

The potential vortex or free vortex is a classic example of an irrotational potential flow.

In the free vortex all fluid particles move as in the solid vortex on concentric circular tracks, but the velocity and pressure distribution is completely different. In particular, co-moving fluid particles rotate at a solids vortex around its own axis, without being deformed, the potential vortex, however, they are deformed, but despite having a motion with the vortex always in the same direction.

Examples of a potential vortex are the bathtub drain, but also a good approximation a tornado.