vortex

A vortex is a region of fluid flow where the motion revolves around an axis line, creating a swirling motion. In a vortex, fluid elements tend to move in circles around a common center, leading to a concentrated rotational motion known as vorticity. Vortices occur in gases and liquids and can range from microscopic to atmospheric scales. Common examples include whirlpools, smoke rings, tornadoes, and cyclones.

Vortices form where angular momentum is conserved and where shear, buoyancy, or obstacles generate rotation. In viscous fluids, vorticity is generated at boundaries and diffuses inward, often producing a core with lower pressure that sustains the swirl. The size and lifetime of a vortex depend on the fluid's viscosity, density, driving forces, and ambient flow.

There are many kinds of vortices. Atmospheric vortices include tornadoes, dust devils, and hurricanes; aquatic vortices include water whirlpools and eddies. In engineering and physics, patterns such as the von Kármán vortex street describe alternating vortices shed behind a bluff body. In fluids, stable structures such as vortex rings can propagate while maintaining their shape for some distance.

Mathematically, vorticity is the curl of the velocity field and measures local rotation. Circulation is the line integral of velocity around a closed loop. For ideal, inviscid fluids, circulation is conserved (Kelvin’s theorem); in real fluids, viscosity enables vorticity to diffuse and be generated at boundaries.

Observing vortices commonly uses smoke, dye, or particle tracking; numerical simulations and laboratory experiments help study their formation and interactions. Vortices play important roles in weather systems, ocean currents, aerodynamics, and astrophysical flows.