Two-Dimensional Experimental Investigation on the Effects of a Fowler Flap Gap and Overlap Size on the Wake Flow Field

Abstract

This work details an experimental investigation on the effects of the variation of flap gap and overlap sizes on the flow field in the wake of a wing-section equipped with a trailing edge Fowler flap. The airfoil was based on the NACA 0014-1.10 40/1.051 profile, and the flap was deployed with 40 deg deflection angle. Two-dimensional (2D) particle image velocimetry (PIV) measurements of the flow field in the vicinity of the main wing trailing edge and the flap region were performed for the optimal flap gap and overlap, as well as for flap gap and overlap increases of 2% and 4% chord beyond optimal, at angles of attack of 0 deg, 10 deg, and 12 deg. For all the configurations investigated, the flow over the flap was found to be fully stalled. At zero angle of attack, increasing the flap gap size was found to have minor effects on the flow field but increased flap overlap resulted in misalignment between the main wing boundary layer (BL) flow and the slot flow that forced the flow in the trailing edge region of the main wing to separate. When the angle of attack was increased to near stall conditions (at angle of attack of 12 deg), increasing the flap gap was found to energize and improve the flow in the trailing edge region of the main wing, whereas increased flap overlap further promoted flow separation on the main wing suction surface possibly steering the wing into stall.

Numerical Investigation of Flow Characteristics of a Slotted NACA 4414 Airfoil

“…A large amount of research is available in the understanding of boundary layer separation reduction and the re-lamination of the airflow to the airfoil via the use of flaps [6]- [9]. Such airfoils are termed as high lift airfoils.…”

“…To further improve the lift of a fowler flap, an additional flap can be incorporated into the design to create a double slotted flap. Overall, trailing edge devices show an upward shift in the lift curve compared to the original airfoil [9]. However, due to the complexity of multi-element high lift airfoils, they are costly.…”