Future aircraft wings will be able to adapt their shape mid-flight

Simulated air vorteces around an aricraft wing section

A team of scientists developed and optimised a concept for wing components that, thanks to electrically driven actuators, are able to adapt their shape as well as their vibratory behaviour during flight. This design considerably improves an aircraft’s aerodynamic performance and reduces fuel consumption. To achieve their remarkable results, the team performed extensive simulations using PRACE supercomputing resources in order to understand and control the turbulence around aircraft wings.

Until now, aircraft wings were mostly rigid. They do comprise a few moving parts, such as the ailerons that control the aircraft’s manoeuvrability or the high-lift flaps that protrude from the rear of the wings and increase lift during take-off and landing. But like the main wings, these smaller parts are also in themselves rigid. “This rigidity has gross aerodynamic disadvantages”, says Dr. Marianna Braza, director of research at CNRS, Institut de Mécanique des Fluides de Toulouse (IMFT), France.

In an intense effort within the EU-funded Smart Morphing & Sensing (SMS) project, Braza and her co-workers in a multidisciplinary team of IMFT and the LAPLACE Laboratories developed a novel concept for aircraft wings that can do more: they adapt their shape to changing conditions in the sky by morphing motions and thus improve flight efficiency. Specifically, the team created the concept and prototypes of the wing’s rear part and of an adaptable high-lift flap for the Airbus A320 family of aircrafts. To develop and perfect their design, the scientists carried out experiments in a wind tunnel and performed extensive high-fidelity numerical simulations at PRACE supercomputing facilities.

A320 aircraft wing with high-lift flap highlighted

The A320 aircraft uses the high-lift flap protruding from the rear of the wing primarily to spur its lift in the slow flight phases during take-off and landing.
Image credit: M. Braza

Solving a conundrum

The result is convincing: The novel wing components not only increase the lift of the aircraft and reduce its drag — thereby increasing flight efficiency and reducing fuel consumption and pollution — but also uniquely diminish noise during take-off and landing. “Until now, whenever an alteration has managed to reduce drag, it has increased noise, and vice versa”, explains Braza.

The fluid mechanics engineer compares the new flexible design to how birds of prey operate in flight. “The bird’s sensing system captures pressure fluctuations in the air in real time and proceeds to adapt its muscle movement and the use of the wing’s different feather types to optimise aerodynamic performance.” In a similar way, the components of the team’s novel concept measure current wind and pressure conditions and adapt the shape and vibratory behaviour of the wing components accordingly.

The simulation of the flow around the A320 wing in cruise reveals the large-scale turbulent vortices occurring around the wing and in its wake. Thanks to the virtual injection of dust, the streaklines of the vortices are illustrated.
Video credit: J.B. Tô, M. Braza

The aerodynamic performance is adapted through three functional entities: First, the sensing system consisting of small and lightweight, but highly accurate, optical sensors takes pressure measurements in real time during flight, thereby enabling adaptations depending on the turbulence around the wing; then, the system of electroactive actuators execute a large-scale morphing motion by changing the cambering of the high-lift flap, meaning the component’s bending in the flight direction — a property that strongly affects turbulence and therefore lift and drag of the aircraft in varying conditions; lastly, an array of small piezo-electric elements at the rear of the wing component operate in sync to create specific vibrations that break a specific class of the usually occurring, small-scale turbulent vortices that apply drag on the airplane.

Good vibrations

Braza and her co-workers performed high-fidelity simulations using the numerical code NSMB (Navier Stokes Multi Block) and coupled them with structural mechanics calculations in order to probe and improve the design of the morphing motion as well as the character of the vibration introduced by the shape memory elements. The team modelled a real-scale section of an A320 wing and a corresponding high-lift flap, which helped them to better understand the nature of the turbulence structure occurring around airplane wings and how to modify it.

Simulated air vorteces around an aricraft wing section.

The image shows the novel prototype with the morphing and vibration capabilities in a simulated take-off. With the simulations, the pressure field and the streamlines and vortices in the wake of the wing-flap are analysed in various configurations.
Image credit: A. Marouf, M. Braza

The simulations showed, among other things, that specific vibrations introduced at the rear of the wings enact considerable influence on a large area around the wings, and that such vibrations can modify turbulence structure very favourably by steering beneficial vortices and breaking down harmful ones. By examining different vibration modes and frequencies, the team found that vibration at a frequency of 300 Hertz attenuates dragging large scale-scale air vortices in the wake of the wings and, at the same time, enhances vortices that produce lift.

Let wings be moved

The high-fidelity simulations also provided valuable insights into how to modulate the camber of the rear of the wing and the high-lift flap. Instead of having a rigid surface, the team’s new high-lift flap design is adjustable in its cambering through electroactive actuators, more specifically, through shape memory alloys. These components were developed to be lighter and move faster than conventional mechanical and hydromechanical parts, and they are therefore better suited for quick adaptations to changing conditions.

One of the limiting factors of flight efficiency is large-scale turbulences forming above and in the wake of the wing, as these air cushions add to the volume of the wing and increase the overall aerodynamic resistance. To tackle this problem, Braza and her co-workers used the simulations to probe different designs and placements of the actuators that execute the morphing, and then combined these motions with different wing incident angles, meaning the angle between the wing plane and the body of the aircraft. The results were clear: “With adequate morphing of the high-lift flap, these unfavourable turbulences can be reduced significantly”, she explains. In fact, the team found that by optimising the shape of the high-lift flap, lift is increased and drag decreased at all wing incident angles.

From a wing section to a drone

As the simulations showed, the novel concept for the high-lift flap has many potential benefits. The comparatively small vibration movement alone is responsible for an overall increase of lift by 4 percent in take-off and landing phases. The combined cambering and vibration motions — the so-called hybrid morphing — applied on the whole aircraft boost its lift by 7 percent. This leads to an increase in aerodynamic efficiency by 4 percent, and aerodynamic noise is simultaneously decreased by 10 to 15 percent. In the cruise phase, a reduction of 9 percent in the airplane drag is obtained by hybrid morphing of the rear part of the wing. As a next step, the concept will be applied on an aircraft of intermediate size — an unmanned drone with a wingspan of 6 meters — to be tested for the first time in real flight.

Project title: FWING – Future smart Wing design

Resources awarded: 16th call: 15 million core hours on Joliot-Curie (SKL) hosted by CEA at GENCI, France

Research field: Engineering

Acknowledgements: The work has been funded within three national projects – EMMAV, DYNAMORPH and SMARTWING – primarily by the Foundation STAE (Sciences et Technologies pour l’Aeronautique et l’Espace). This allowed the creation of the multidisciplinary team between the laboratories at IMFT and LAPLACE within the Smart Morphing Centre (SMC) in Toulouse, coordinated by IMFT. The work benefited from a collaboration with Airbus Emerging Technologies and Concepts Toulouse (ETCT).

References:

Simiriotis N., Jodin G., Marouf A., Elyakime P., Hoarau Y., Hunt J.C., Rouchon J.F. and Braza M. Morphing of a supercritical wing by means of trailing edge deformation and vibration at high Reynolds numbers: experimental and numerical investigation, J. Fluids Struct (2019)
https://doi.org/10.1016/j.jfluidstructs.2019.06.016

Tô, J.-B., Simiriotis, N., Marouf, A., Szoubert, D., Asproulias, I., Zilli, D.M., Hoarau, Y., Hunt, J.C.R. and Braza, M.: Effects of vibrating and deformed trailing edge of a morphing supercritical airfoil in transonic regime by numerical simulation at high Reynolds number. J Fluids Struct (2019)
https://www.sciencedirect.com/science/article/abs/pii/S0889974619300271

Marouf, A., Bmegaptche Tekap, Y., Simiriotis, N., Tô, J.-B., Rouchon, J.-F., Hoarau, Y. and Braza, M.: Numerical investigation of frequency-amplitude effects of dynamic morphing for a high-lift configuration at high Reynolds number. Int. J. Numer. Method. H. (2019)
https://www.emerald.com/insight/content/doi/10.1108/HFF-07-2019-0559/full/html

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