Wings of modern civil airliners are designed for two distinct and very different flight phases: Cruise and low-speed-flight. As an aircraft spends the majority of each mission in cruise, this is what its aerodynamics are optimized for. In order to generate sufficient lift during low-speed flight phases, namely take-off and landing, concurrent aircraft are equipped with mechanical high-lift devices (e.g. slats and flaps), which extend the flight envelope. While, for decades, those 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 require a different solution. In particular, one novel design feature conflicts with the local integration of mechanical high-lift devices at the wing’s leading edge: ultra-high-bypass ratio fans (UHBR). 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 be introduced to delay local separation to higher angles of attack and therefore to augment the overall high-lift system.

The aim of flow control is, generally speaking, 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.

Using numerical and experimental methods, flow control actuator systems at two different scales were developed:
During the first phase, a small-scale actuator system, fitting a 1:13.6 scale wind tunnel model was developed, manufactured and qualified. This system was employed in two wind tunnel test campaigns conducted in the cryogenic test facility (KKK) in Cologne, Germany. The results of the campaign underpinned the potential of active flow control to counter the lift loss due to the increased slat cut-out required to enable the installation of UHBR nacelles. During the second phase of the project, a real-scale actuator – ready for integration into an A320 flight-test airplane – was developed, built and qualified in a lab environment. The successful development of this demonstrator did not only respect aerodynamic requirements, but also took aspects such as the overall aircraft infrastructure, noise emission and system health monitoring into account.

The project furthered significant advances in flow control actuator design and integration, ranging from considerations of scalability to valuable lessons learnt with respect to manufacturability.

Publications linked to the project:

  • N. Karcher; Surrogate Based Optimization of a Fluid Actuator for the Aeronautics Industry, 5th OpenFOAM User Conference 2017, Wiesbaden, 2017
  • V. Ciobaca, B. Stefes, A. de Bruin, M. Bauer, P. Schlösser, A. de Blécourt, N. Bier, J. Zhai, M. Meyer, J. Wild; Wind Tunnel Experiments with Local Active Flow Control for Aircraft towards Future Flight Testing, 31st Congress of the International Council of the Aeronautical Sciences, 2018

This project has received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 715796.