What is the purpose of boundary layer fences on swept-wing designs?

Boundary layer fences are primarily used on swept-wing designs to improve low-speed characteristics. These fences help control the behavior of the boundary layer—the thin layer of air that interacts with the wing surface. At lower speeds, especially during takeoff and landing or when the aircraft is operating at high angles of attack, the flow can become turbulent or separate from the wing. By utilizing boundary layer fences, airflow over the wing is better managed, which helps maintain attached flow and improves overall lift performance. As a result, this leads to enhanced stability and control in critical phases of flight, making the airplane more predictable and easier to handle under such conditions.

While other options might seem relevant, they do not specifically address the primary function of boundary layer fences in enhancing low-speed aerodynamic performance, which is crucial for safe aircraft operations.