Which device for controlling lift allows air to flow from the lower surface to the upper surface at high angles of attack?

Slat

Explanation:

In the field of aero-space engineering, there exist a system that produces an increased amount of lift produced by the aircraft's wing. This mechanism is know as a high lift device.

The device could either be movable or fixed. types of movable devices are flaps and slats and fixed devices are leading edge root extensions, slots and boundary layer systems.

The slat is a small aerofoil shaped device which pushes the airflow from the lower surface the upper surface when at a high angle of attack. This pushes airflow at the front of the wing and also allows the wing to be operated at the higher angles required to produce more lift. The gap between a slat and a wing is a slot.