Installing ultra-high–bypass ratio (UHBR) fans is one way to tackle environmental, carbon tax and jet fuel tax issues. However, their installation conflicts with the local integration of mechanical high-lift devices at the wing’s leading edge. The large nacelles – housing that usually holds engines or some other equipment in an aircraft – of UHBR engines need to be installed close to the wing to provide sufficient ground clearance without increasing the size of an aircraft’s landing gear. Consequently, a slat (high-lift device) would collide with the nacelle when deployed, resulting in the need for a slat cutout, the fraction of the wing’s span above the engine where no slat is installed. This leaves regions of the wing unprotected by a slat and prone to separation at incidence angles much lower than for the remaining wing sections. It’s in these regions where active flow control (AFC) can act as an enabler since it delays local separation to higher angles of attack, thus augmenting the overall high-lift system.
Towards state-of-the-art AFC actuator systems
Successful application of AFC requires the availability of robust and reliable AFC actuators. The EU-funded DECOROUS project focused on the development of such actuators, namely a two-stage, no-moving–parts fluid actuator system for use in AFC applications at the wing-pylon junction of civil airliners. “This will pave the way for UHBR engines,” says coordinator Dr Matthias Bauer. “Based on technology researched in previous projects, DECOROUS goes far beyond their scope by including real aircraft constraints and harsh environment conditions, and considering disciplines beyond aerodynamics.” Project partners developed, manufactured and validated a small-scale pulsed jet actuator (PJA). This was then integrated into a 1:13.6-scale wind tunnel model for cryogenic testing involving flow control at the wing-pylon junction. This was done to quantify the flow control attempt’s efficiency. They optimised the AFC technology, taking into account aspects such as aeroacoustics and integration. The team also developed and validated a real-scale PJA for integration into a flight test Airbus 320 aircraft. “Its successful development didn’t only respect aerodynamic requirements, but also considered overall aircraft infrastructure, noise emissions and system health monitoring,” notes Dr Bauer.
Advancing AFC actuator design and integration
By developing a very-small–scale flow control actuator without moving or electrical components, the researchers were able to make the AFC technology testing in cryogenic conditions with the scale model possible. They conducted a cost-benefit analysis of AFC applied to a civil airliner and identified potential showstoppers on the road. The DECOROUS team addressed previously underinvestigated AFC technology aspects. Research on aeroacoustics revealed significant noise sources that could impact passenger comfort. Team members proposed solutions to this problem. They also investigated the integration of the AFC actuators into the overall aircraft environment, identifying modifications necessary for installing the required components on a flight test aircraft. Dr Bauer adds: “All this work brought the AFC technology to the brink of market readiness.” “Thanks to DECOROUS, the European aeronautical industry is now capable of using AFC as a tool to design next-generation eco- and cost-efficient civil aircraft while sustaining the sector’s growth,” concludes Dr Bauer.
DECOROUS, AFC, aircraft, flow control, AFC actuator, slat, UHBR, PJA