Vortex
Introduction
A vortex is a region within a fluid where the flow revolves around an axis line. The axis line may be straight or curved, and the fluid may be a liquid or a gas. Vortices are a major component of turbulent flow. The distribution of velocity, vorticity (the curl of the flow velocity), as well as the concept of circulation are used to characterize vortices. In most vortices, the fluid flow velocity is greatest next to its axis and decreases in inverse proportion to the distance from the axis.
Formation
Vortices can be created by a variety of physical phenomena, including the differential heating of air (which leads to the formation of tornadoes), the behavior of liquids and gases in certain geometrical settings (such as the vortex that forms in a stirred cup of tea), and the aerodynamic properties of certain objects (such as the vortices that form over the wings of a rapidly moving airplane).
Types of Vortices
There are several different types of vortices, each with its own unique properties and behaviors.
Free Vortices
Free vortices, like smoke rings, have a velocity that is proportional to the inverse of the distance from the center. They are not constrained by the surface of a container and can move freely through the fluid in which they are embedded.
Forced Vortices
Forced vortices, such as the whirlpool that forms when a bathtub is drained, have a velocity that is proportional to the distance from the center. They are often caused by a source of mechanical energy, such as a pump or a stirring device.
Vortex Rings
Vortex rings are donut-shaped vortices that are typically formed by the ejection of fluid from a circular orifice. They are common in nature and can be observed in phenomena such as smoke rings, bubble rings, and the rings of fluid that form when a droplet impacts a surface.
Vortex Filaments
Vortex filaments are vortices that are confined to a curve, or filament. They are a useful mathematical abstraction for understanding the dynamics of vortices in three dimensions.
Vortices in Fluid Dynamics
In fluid dynamics, vortices are used to study a variety of phenomena. They are fundamental to the study of turbulence, a complex and still not fully understood aspect of fluid dynamics. Vortices also play a key role in the study of aerodynamics, where they help explain the lift generated by airplane wings and the behavior of air over different types of terrain.
Vortices in Meteorology
In meteorology, vortices are an important component of weather systems. The most dramatic examples are tornadoes and hurricanes, but vortices also play a role in less severe weather phenomena, such as dust devils and waterspouts.
Vortices in Astrophysics
In astrophysics, vortices are thought to play a role in the formation of stars and galaxies. They are also a key element in the study of black holes, where they help explain the behavior of matter and energy near the event horizon.
Vortices in Engineering
In engineering, understanding the behavior of vortices is crucial for designing efficient and safe structures and vehicles. For example, engineers must account for the vortices that form around bridge piers, which can cause erosion and structural damage. Similarly, the vortices that form around aircraft wings can affect the aircraft's stability and control.
