Span wise flow is caused by the difference in air pressure on the wing. What is its direction of movement?

Span wise flow refers to the airflow that occurs along the wingspan of an aircraft, particularly in relation to the pressure differences that exist on the top and bottom surfaces of the wing. In the context of the question, the correct understanding is that as air moves over and under the wing, it is influenced by the pressure variations that occur due to lift generation.

The direction of span wise flow is towards the lower pressure area, which is typically located on the upper surface of the wing. This means that the airflow moves from the higher pressure region, generally beneath the wing, to the lower pressure region located atop the wing. This movement occurs primarily through the wing tip, as the airflow seeks equilibrium due to the differential pressures created during flight.

Thus, the span wise flow being described accurately reflects this movement, which is directed from beneath the wing to the top of the wing through the wing tip. Understanding the dynamics of this flow is crucial for grasping how lift is generated and how it contributes to the overall aerodynamics of an aircraft.