How do vortex generators improve airflow over a wing?

• A. They energize the air helically and it rolls along the airfoil and stays attached.
• B. They reduce drag by smoothing the surface.
• C. They increase wing area.
• D. They create downward pressure on the upper surface.

Answer: (A)

The main idea is that vortex generators energize the boundary layer to prevent flow separation. They generate small, spanwise vortices that mix higher-energy air from above the surface into the slower air right next to the wing. This added momentum in the boundary layer helps it resist the adverse pressure gradient that tends to peel the flow away from the wing, so the air stays attached to the surface longer and the wing maintains lift, especially at high angles of attack or near stall. The description of energizing the air and having it roll along the airfoil captures this mechanism. The other choices miss the point: vortex generators don’t smooth the surface to reduce drag, they don’t increase wing area, and they don’t purposefully create downward pressure on the upper surface.