Which aerodynamic phenomenon occurs when air moves over the top of an airfoil and downward?

Which aerodynamic phenomenon occurs when air moves over the top of an airfoil and downward?

• A. Upwash
• B. Boundary Layer
• C. Downwash
• D. Turbulence

Answer: (C)

Airflow is redirected downward as it leaves the wing, which is called downwash. When an airfoil generates lift, the surrounding air must bend downward behind the wing to satisfy the circulation of flow around it. This downward deflection of the airflow creates an upward reaction force on the wing (lift) per Newton’s third law. The wake behind the wing features air moving downward, embodying the downwash. Upwash would be an upward deflection of air, which isn’t what’s described here. The boundary layer is just the thin layer of air in contact with the surface, and turbulence refers to chaotic, irregular flow fluctuations—neither of which capture the downward deflection of the trailing air.

Airflow is redirected downward as it leaves the wing, which is called downwash. When an airfoil generates lift, the surrounding air must bend downward behind the wing to satisfy the circulation of flow around it. This downward deflection of the airflow creates an upward reaction force on the wing (lift) per Newton’s third law. The wake behind the wing features air moving downward, embodying the downwash.

Upwash would be an upward deflection of air, which isn’t what’s described here. The boundary layer is just the thin layer of air in contact with the surface, and turbulence refers to chaotic, irregular flow fluctuations—neither of which capture the downward deflection of the trailing air.