While, for decades, mechanical devices resolved the dilemma of having to cover efficiently for high- and low-speed flight, recent developments in aircraft design have turned up new problems that might require a different solution. Those developments, driven by spiking energy prices, fierce competition and environmental responsibility of the aircraft manufacturers, aim at increasing the aircraft’s fuel efficiency to reduce direct operating costs and the its ecological footprint. The recent discussion on climate change has moved all those aspects even more to the center of attention: With flying becoming a socially less acceptable form of travel due to its environmental impact, the threatening CO2 emission tax and the idea to end tax exemption of aircraft fuel, groundbreaking new technologies are needed to sustain the growth of the aeronautics industry in Europe.
For aircraft, high bypass ratios of the jet engine are beneficial for the propulsion efficiency and therefore installing ultra-high-bypass ratio fans (UHBR) is one way to go to address those challenges. However, on a technical level, their integration conflicts with the local integration of mechanical high-lift devices at the wing’s leading edge. The large nacelles of UHBR engines need to be installed close to the wing to provide sufficient ground clearance without increasing the size of the aircraft’s landing gear. In consequence, a slat would collide with the nacelle when deployed, resulting in the need of a slat cut-out, 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 sections of the wing. It is in those regions where Active Flow Control (AFC) can act as an enabler since it allows to delay local separation to higher angles of attack and therefore to augment the overall high-lift system.
The aim of flow control is to modify this original state of flow in such a manner that beneficial effects are achieved. Besides the in-depth understanding of the flow physics involved, successful application of active flow control requires the availability of robust, reliable and potent flow control actuators. The project DECOROUS addresses the development of such actuators, namely of a two-stage no-moving-parts fluidic actuator system for use in active flow control applications at the wing-pylon junction of civil airliners – paving the path for UHBR engines. The work is based on the technology researched in the EC-funded projects DT-FA-AFC, FloCoSys, and robustAFC, but goes vastly beyond the scope of those projects by broadening the view to include real-aircraft constraints, considerations from other-than-aerodynamics disciplines, and harsh environment conditions.
The overall objective of this project was to contribute a cornerstone of flow control technology: effective and robust flow control actuators. It had to provide suitable flow control actuators for cryogenic wind tunnel testing to advance the aerodynamic understanding of this method to realistic model geometries and Reynolds number. It had to resolve challenges from a multidisciplinary point of view – considering aspects such as certifiability, passenger comfort and manufacturing. Finally, it had to provide a flow control system for an A320 test aircraft, to enable actual flight testing of the technology and thereby reaching a technology readiness level that allows European aircraft manufacturers to move the technology from RTD to product.
