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Design, test, and manufacturing of robust fluidic actuators

Periodic Reporting for period 2 - DECOROUS (Design, test, and manufacturing of robust fluidic actuators)

Reporting period: 2017-12-01 to 2019-05-31

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.
Within the project a small-scale pulsed jet actuator (PJA) was developed, manufactured and validated before supplying it for integration into a 1:13.6 scale wind tunnel model for cryogenic testing of flow control at the wing-pylon junction. Those tests were supported with aerodynamic expertise and all support data necessary to quantify the efficiency of the flow control attempt. The actuator technology was optimized in a multidisciplinary approach, considering aspects such as aeroacoustics and integration. Based on all learning, a real scale PJA for integration in a flight test aircraft was developed and validated experimentally.
The project DECOROUS developed a very small-scale flow control actuator without moving or electrical components, which made testing of AFC technology in cryogenic conditions with a half-model of scale 1:13.6 possible in the first place. The learnings from this work has since informed two (industry-funded) test campaigns on a model at similar scale. With this actuator system, two extensive high-Reynolds number test campaigns were conducted with support of DECOROUS that qualified for TRL3. The results of those tests did not only quantify the actual benefit to be expected from AFC at the wing-pylon junction and gave valuable insight into the aerodynamic aspects of this complex configuration, but it also allowed to extrapolate the required momentum and mass flow necessary to realize the desired effect on a real aircraft. The latter aspect enabled – for the first time – to conduct a cost-benefit analysis of flow control applied to a civil airliner and identified potential showstoppers on the road. This work also informed the multidisciplinary optimization aspect of this project. The multidisciplinary approach allowed to address several previously under-investigated aspects of the flow control technology, since research on this topic usually focuses on aerodynamics rather than including a broader view. Here, the study of aeroacoustics revealed significant noise sources, which could impact passenger comfort, and solutions to this problem were proposed. One major aspect was the study on integration of the flow control actuators into the overall aircraft environment, conducted together with Airbus, which identified the modifications necessary (to the flow control system and to the aircraft) to allow for installation of the required components on a flight-test aircraft. Thus, this work impacted the ability of performing TRL6 tests and therefore brought the AFC technology to the brink of market readiness. A practical result of the project was the development and validation of pulsed jet actuator for a real aircraft, which ca be used for TRL6 flight testing.
The cluster of projects DECOROUS interfaced with during the last three years (i.e. the EC-funded Aflotest and Flowcaash) and the different partners involved (i.e. Airbus, DLR, NLR) significantly contributed to the maturation of AFC on a civil aircraft configuration – for UHBR integration in particular, but also for a broad range of applications at different locations, such as the VTP or the wingtip. This enables the European aeronautics industry to quantify the benefit and the risks associated with introducing this new technology into the aircraft structure and adds a tool to the toolbox of aerodynamic design.
Thus, the overall impact of this project is on the capability of the European aeronautical industry to use active flow control as a tool to design next generation – eco-efficient and cost-efficient – civil aircraft.
Image of real scale PJA during experimental validation
Simulation result: pulsed jet actuator used for the second wind tunnel entry
Simulation result: pulsed jet actuator
Why is AFC necessary? Why is AFC necessary? Regions prone to separation at high angles of attack on
Image of wing leading edge insert (without plenum cover) equipped with local GN2 heater, AFC system
Simulation result: steady blowing actuator
Internal structure of a two stage pulsed jet actuation system