Definition
In aerodynamics, circulation is the net rotational flow of air around an object such as an airfoil or a spinning cylinder. It is the component of airflow that moves around the object in a closed loop, superimposed on the general airflow passing over it. This circulating flow is what causes the air to move faster on one side and slower on the other, producing a pressure difference and therefore lift.
Plain English
Circulation is the looping motion of air around a wing or spinning object. When air loops around in this way, it speeds up on one side and slows down on the other, and that difference is what creates lift.
Context Anchor
Seen in lift discussions, especially when explaining the Magnus Effect and how airflow around an object can create lift.
Derivation
From the Latin circulatio, meaning 'a moving in a circle.' The aviation use keeps that core idea: air moving in a loop around the object, not just past it.
Why Pilots Care
It explains unexpected forces on spinning objects such as propellers, golf balls, or wings in crosswind conditions, directly affecting trajectory, control, and safety.
Grounding Statement
Picture a spinning ball moving through the air: the air drags around with the spin, looping around the ball. That loop is circulation, and it's what pushes the ball sideways.
Intuition Check
Circulation does not mean cabin air movement or blood flow here. It means a rotating pattern of air around an object that affects lift.
Example Sentence 1
The Magnus effect is explained by the circulation of air around a spinning cylinder, which produces a pressure difference and a sideways force.
Example Sentence 2
Greater circulation around the wing at higher angles of attack allows the aircraft to generate more lift before stall.