vortex line

In physics, a vortex line is the axis around which fluid circulates, often seen in phenomena like whirlpools and typhoons. While the fluid outside the core of a vortex may appear to be rotating without local vorticity, the circulation around a loop enclosing the vortex line is not zero. This concept is crucial in fluid dynamics, particularly when dealing with potential flow with circulation, where the fluid's behavior is analogous to electromagnetic fields. The Magnus effect, which explains how rotating cylinders generate a force in a fluid, is an example of this principle. Vortex lines can also form closed rings, like smoke rings, which move along their axis.1