High-lift performance enhancement of a fowler flap using aerodynamic flow control

The performance of multielement airfoils in high-lift configuration is typically improved by optimizing the location and height of the cross-stream gap between elements that forms a cove wall-jet to mitigate flow separation over the airfoil. In the present wind tunnel investigations, the high-lift performance of an airfoil with a Fowler flap is enhanced using active, fluidic-based aerodynamic flow control implemented by spanwise arrays of fluidically oscillating jets near the leading edge of the flap. The actuation jets manipulate the interaction between the main element boundary layer and the cove jet to overcome flow separation over the flap and yield high-lift performance that is comparable to or better than conventional high-lift airfoils. Fluidic actuation enables effective operation at larger flap deflections while diminishing the sensitivity to gap characteristics. It is demonstrated that, in addition to jet momentum coefficient, the performance of the actuator array is sensitive to the characteristic spanwise spacing (or wavelength) of the jets. Specifically, the lift increment per jet increases with spanwise wavelength and ultimately becomes invariant as spanwise jet interactions diminish. It is also shown how the aerodynamic loads scale with the number of active jets and a characteristic spanwise wavelength is identified for which jet density can be optimized with minimal losses in performance.