You are here

High Lift Enhancement using Fluidic Actuation

The design and performance of transport aircraft are influenced substantially by the effectiveness of the aerodynamic control system, affecting characteristics such as maximum takeoff weight, required runway length and fuel consumption.  Many conventional control systems are complex and consist of multiple elements with intricate positioning mechanisms that are designed to maximize performance and efficiency.  Active flow control (AFC) provides a means for reducing weight, part count and fabrication cost while improving cruise efficiency, creating the potential for significantly enhanced performance compared to what is possible using conventional technologies.

It is demonstrated how AFC can be used to fluidically manipulate the aerodynamic characteristics of an airfoil with a high-lift system based on a commercial aircraft configuration in a manner that improves high-lift performance.  Actuation is provided by fluidic oscillators or synthetic jet actuators that are integrated to the airfoil surface and function by engendering and manipulating concentrations of vorticity near the surface, affecting the accumulation and shedding of vorticity around the airfoil.  The effectiveness of the actuation and the resulting changes in concentrations of trapped vorticity are varied by altering the momentum coefficient Cm and other actuator operating conditions, leading to changes in the flow around the entire airfoil and the associated aerodynamic forces and moments.  In particular, actuation issuing from the junction between a trailing-edge flap and the main airfoil body (Figure 1, δ = 40º) can be used to achieve a substantial lift increment.

The lift increment can be demonstrated through a series of spanwise vorticity measurements over the flap downstream of the shoulder including the actuator orifice (Figure 2).  In the absence of actuation, the flow separates downstream of the actuator, forming a (nearly) free shear layer that bounds the wake from above.  Actuation concentrates the boundary layer near the surface, causing the flow to turn toward the wall.  At Cμ = 1.6% (as shown) the flow remains attached along nearly the entire flap and is deflected downward resulting in a significant increase in lift.

Supported by Boeing