vortex

i. In meteorology, any rotary flow in the atmosphere.

ii. As used in aerodynamics, circular patterns of air created by the movement of an airfoil through the air when generating lift. As an airfoil moves through the atmosphere in sustained flight, an area of low pressure is created above it. The air flowing from the high-pressure area to the low-pressure area around and about the tips of the airfoil tends to roll up into two rapidly rotating vortices, cylindrical in shape. These vortices are the most predominant parts of aircraft wake turbulence, and their rotational force is dependent upon the wing loading, gross weight, and speed of the generating aircraft. The most important factor is weight. The greatest vortex strength occurs when the generating aircraft is heavy, clean, and slow. This situation occurs soon after a takeoff. Peak vortex tangential speeds of 300 ft/s have been recorded. A vortex can induce roll and, in rare cases, cause structural damage to the aircraft that is following the aircraft generating the vortex. The vortices from medium and heavy aircraft can be extremely hazardous to smaller aircraft, especially during takeoff and landing behind the larger aircraft.

Vortex streamline flow.