The vortex ring, also called toroidal vortex , is a torous vortex in a liquid or gas; ie an area where the liquid mostly rotates around the imaginary axis line that forms a closed loop. The dominant flow in the vortex ring is said to be toroidal, more precisely poloid.
The vortex ring is abundant in the fluid flow of fluid and gas, but is rarely noticed unless the fluid motion is revealed by suspended particles - such as in the smoke circle often deliberately or accidentally produced by smokers. The vortex ring is also a trick commonly produced by fire eaters. Visible vortex rings can also be formed by certain artillery shells, in mushroom clouds, and in microbursts.
Vortex rings usually tend to move in a direction perpendicular to the plane of the ring and such that the inner edge of the ring moves ahead faster than the outer edge. In the body of a stationary fluid, the vortex ring can travel for a relatively long distance, carrying a spinning fluid with it.
Video Vortex ring
Structure
In typical vortex rings, the fluid particles move around the circular path around an imaginary circle ( core ) perpendicular to the path. As in any vortex, the fluid velocity is approximately constant except near the nucleus, so the angular velocity increases toward the nucleus, and most vortices (and hence most energy dissipation) are concentrated nearby.
Unlike the ocean waves, whose motion is only real, the moving swirling ring actually carries the spinning fluid together. Just as the spinning wheel reduces friction between the car and the ground, the poloid flow from the vortex reduces friction between the core and the surrounding silent fluid, allowing it to travel long distances with relatively small mass and kinetic energy and little change in size or shape. Thus, the vortex rings can carry the mass farther and with less dispersion than liquid jets. That explains, for example, why a smoke ring keeps traveling long after every extra smoke is blown out with it has stopped and spread. The properties of this vortex ring are exploited in the ring vortex ring to control melee and vortex ring toys such as air vortex cannons.
Maps Vortex ring
Formation
One way a vortex ring can be formed is to inject a rapidly moving compact fluid mass ( A ) into a stationary liquid mass ( B ) (which may be the same as a liquid). The thickened friction at the interface between the two liquids slows the outer layer A relative to the core. The outer layers then slip around the mass of A and congregate in the back, where they re-enter the mass after the inner part moves faster. The net result is a poloid flow in A that evolves into a vortex ring.
This mechanism is generally seen, for example, when a drop of colored liquid falls into a cup of water. It is also often seen on the leading edge of a lump or liquid jet as it enters a stationary mass; heads like mushrooms ("early boast") that develop on the tip of the jet have a vortex ring structure.
Variants of this process can occur when a jet in the liquid touches a flat surface, as in a microburst. In this case the poloid spinning of the vortex ring is due to the viscous friction between the rapid outflow layer near the surface and the fluid that moves more slowly above it.
Vortex rings are also formed when the fluid mass is impulsively driven from the enclosed space through a narrow gap. In this case the flow of poloids is set in motion, at least in part, by the interaction between the outermost part of the fluid mass and the opening edge. This is how a smoker removes the smoke ring from the mouth, and how most of the vortex ring toys work.
Vortex rings can also form in the wake of a solid object that falls or moves through a liquid with sufficient speed. They can form also in front of objects that suddenly reverse their movement with fluids, such as when producing smoke rings by shaking incense. Vortex rings can also be made by spinning propellers, as in a blender.
Another example
Vortex ring status in helicopter
Air vortices can form around the main rotor of a helicopter, causing a dangerous condition known as the vortex ring state (VRS) or "settling with force". In this condition, the air moving down through the rotor turns outwards, then upwards, into, and then down through the rotor again. This recirculation of streams can eliminate many lifting forces and cause terrible loss of altitude. Applying more power (increasing collective pitch) serves to further accelerate downwash through which the main rotor goes down, aggravating the condition.
Vortex rang in human heart
The vortex ring forms in the left ventricle of the human heart during cardiac relaxation (diastole), as the blood stream enters through the mitral valve. This phenomenon was initially observed in vitro and then reinforced by an analysis based on color Doppler mapping and magnetic resonance imaging. Several recent studies also confirm the presence of vortex rings during the rapid diastole filling phase and imply that the process of forming a vortex ring may affect the mitral dynamics of the annulus.
Bubble ring
Releasing the underwater air bubble ring, which is a vortex water ring with bubbles (or even single donut-shaped bubbles) trapped along the axis line. Such rings are often produced by scuba divers and dolphins.
Theory
Historical study
The vortex rings must have been known for as long as people have smoked, but a scientific understanding of their nature must wait for the development of a mathematical model of fluid dynamics, such as the Navier-Stokes equation.
The Vortex Ring was first analyzed mathematically by the German physicist Hermann von Helmholtz, in his 1858 paper On Integral Hydrodynamic Expression of Vortex-motion . The formation, movement and interaction of vortex rings have been studied extensively.
Ball Vortices
For many purposes, the ring vortex can be estimated to have a small cross section vortex core. But a simple theoretical solution, called Hill ball vortex after English mathematician Micaiah John Muller Hill (1856-1929), is known where vortices are distributed in spheres (the internal symmetry of this flow remains annular). Such structures or electromagnetic equivalents have been suggested as an explanation for the internal structure of the light bulb. For example, Shafranov uses a magnetohydrodynamic (MHD) analogy to the mechanical vortex of Hill fluid to consider the axial symmetrical MHD configuration conditions, reducing the problem of stationary flow theory of uncompressible fluids. In axial symmetry, he considers the general equilibrium for distributed currents and is concluded under the Virial Theorem that if there is no gravity, the limited equilibrium configuration can exist only in the presence of an azimuthal current.
Instability
A symmetrical type of azimuth beam is observed by Maxworthy when the vortex ring moves around a critical velocity, which lies between turbulence and the laminar state. Then Huang and Chan report that if the initial condition of the vortex ring is not perfectly circular, another kind of instability will occur. An elliptical vortex ring undergoes an oscillation where it is first stretched in a vertical direction and squeezed in a horizontal direction, then passes the intermediate state in which it is circular, then changes its shape in the opposite way (stretching horizontally and vertically) before reversing the process and back to its original state.
See also
- Air vortex cannon
- Bubble ring - underwater vortex ring
- Mushroom clouds
- Toroidal moments
- Vortex ring weapons
- Vortex ring toys
References
External links
- YouTube video from Vortex cannon ring
- A fluid dynamics course that includes vortices
- Animated vortex rings
- The makers of giant vortex rings
- Physics Toy Box: Vortis, Water cannon, and Mushroom Cloud
- Thesis on vortex ring formation and interaction
- Semicircle Vortex in the pool, Dianna Cowern (Physics Girl), YouTube
- More experiments with vortex rings in the pool, Dianna Cowern (Physics Girl), YouTube
Source of the article : Wikipedia
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