Vortex generators are placed on which wing surface to combat high speed drag separation?

• A. Upper surface of wing
• B. Lower surface
• C. Leading edge
• D. Trailing edge

Answer: (A)

Vortex generators work by creating small, organized vortices that energize the boundary layer. These vortices pull higher-energy air from outside the boundary layer toward the surface, which thickens and speeds up the near-surface flow. That added momentum helps the air stay attached to the wing when the pressure gradient is adverse, especially at higher speeds or in conditions where the wing would otherwise suffer drag-causing separation.

Placing vortex generators on the upper surface is most effective because that's where the adverse pressure gradient and potential separation typically occur on a wing in flight. Energizing the upper-surface boundary layer helps prevent separation there, reducing drag and improving performance. If they were on the lower surface, they wouldn’t address the primary separation region on the upper surface, and would offer little benefit for high-speed drag separation.