In this recent and promising area, a lot of devices are searched to act on the boundary layer, on shock-boundary layer interaction, on separation or on vortex development in order to :
- reduce the drag by active or passive means;
- develop new concepts for improving the behaviour or the control of the aircraft near the limits of the flight envelope or to extend the flight envelope;
- minimise the effect of wake behind large aircraft in take-off or landing configurations.
The control systems concern civil aircrafts, fighters and rotor blades and can be passive or active. MEMS can also be used. For controlling the boundary layer separation due to shock or adverse pressure gradient, the main devices are vortex generators, bump, cavity (passive control) and fluidic systems (blowing or synthetic jet). To reduce the friction drag of turbulent boundary layer, riblets or MEMS can be used. The delay of the transition location is obtained through laminar flow control techniques. The vortex control is realised by mechanical (leading edge flaps) or pneumatic device (forebody and wing vortices). Trailing edge vortex control can be made with adapted trailing edge flaps. Optimisation of rotor blades is also searched to get less vibration and less noise by means of active control without diminishing aerodynamic efficiency (mechanical or pneumatic system).For stealth subsonic airbreathing missile, control devices are needed to prevent separation of the airflow in the short S duct.
(Source: ACARE Domain 104)