Nocturnal laser measurements – first in-flight aerodynamic analysis on a commercial aircraft

07 January 2015

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  • Strömungswirbel im Flug
    Vortices in flight

    Flow vortices over the wing of ATRA become visible with the laser during the test flight. The condensation generated by the vortices make it stand out. To the far left the tip of the wing is indirectly illuminated, and the winglet is visible. The bright line marks the impingement of the light section on the wing.

  • ATRA on approach
    DLR research aircraft ATRA

    ATRA (Advanced Technology Research Aircraft) is the largest member of the DLR research fleet; it has been in service since late 2008.

  • Testlauf im Hangar
    Laser aircraft in the hangar

    DLR researchers in Göttingen developed the Particle Image Velocimetry (PIV) technique. This process involves introducing micron-sized particles into a flow field for analysis, and then using high-performance cameras to register their movements in real time. Instead of using synthetic particles, the DLR researchers are now using water droplets naturally available during in-flight testing. During a test in the hangar, water droplets are sprayed across the wing by hand.

  • Messstation in der Kabine des DLR%2dForschungsflugzeugs ATRA
    Measurement station in the cabin of the DLR ATRA research aircraft

    The laser measurement system provides a three-dimensional visualisation of the airflow over the wing. The laser and the two cameras, which are mounted behind windows in the cabin, can be seen in the background.

  • Lasermessungen über der Tragfläche des ATRA
    Laser measurements on the wing of ATRA

    In the hangar at DLR Braunschweig, researchers test the laser measurement instrumentation on the wing of the DLR research aircraft ATRA (Advanced Technology Research Aircraft). Water droplets become visible in the laser light and cameras mounted behind the cabin windows record their movement.

  • DLR ATRA research aircraft

    The Airbus A320-232 D-ATRA, DLR's largest fleet member, has been in operation since the end of 2008.

Researchers at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), in collaboration with Airbus, have completed a successful world première – for the first time, they have used lasers to visualise the airflow over the wing of a passenger aircraft in flight. They have developed a method that captures the movement of water droplets streaming over the wing, which reveals the smallest movements of the air. These findings will help optimise future wings to enable slower and quieter approach procedures. Another 'laser flight' is scheduled for  8 January 2015.

Visualisation of aerodynamic flow

Christina Politz and her team at the DLR Institute of Aerodynamics and Flow Technology set off from the research airport in Braunschweig for the first nocturnal test flight on board the DLR A320 ATRA (Advanced Technology Research Aircraft) on 6 January 2015. They were in the air for three and a half hours. The preceding weeks were spent making a large number of modifications to the cabin of the former passenger aircraft, fitting an optically diverged laser behind a special window. "Adjacent to the laser, we installed two high-speed cameras to left and right, behind other cabin windows, pointing the laser and the cameras out onto the wings," Politz explains. "This enabled us to use laser illumination to acquire thousands of images of the reflections from water droplets while in the air."

This was truly a new experience for the DLR test pilots, sitting in the cockpit wearing protective goggles; never before have laser beams been directed across the wing of the ATRA research aircraft: "It really was a special experience for me to sit at the controls during this rather unusual first flight," said Hans-Jürgen Berns from the DLR Flight Experiments Facility. "A challenging undertaking, which I managed quite well."

Flying slowly to reduce noise

The researchers are now creating precise 3D animations of the airflow around the wing. "We want to acquire an understanding, in hitherto unachieved precision, of how the airflow behaves around the wings and flaps, and especially around the engine nacelles, during low-speed flight," says Ralf Rudnik from the DLR Institute of Aerodynamics and Flow Technology, who is in charge of the HINVA (High Lift Inflight Validation) project. "Only if we come to a better understanding of the aerodynamic limits during low-speed flight will we have the opportunity to shift these limits to our benefit in the future."

The advantage of this is that commercial aircraft that approach for landing at a lower speed are quieter and can handle shorter runways. Current manufacturer specifications limit the approach speed of passenger aircraft to between 200 and 250 kilometres per hour, with the precise values depending on the type of aircraft and the load. The in-flight test data now being acquired, combined with previous wind tunnel measurements and computational fluid dynamics simulations performed as part of the HINVA project, provide an extensive database. In future, this may permit the development of wings and flap systems that are far better suited to low-speed flight and, in the long term, allow a reduction in the minimum speed restriction around airports. Airbus, as a partner, is supporting the project as part of its own research activities, as the precise predictions of flow processes during take-off and landing that the researchers are seeking will make a substantial contribution to improving future aircraft development.

Real-time measurements 

DLR researchers in Göttingen developed the Particle Image Velocimetry (PIV). This process involves introducing micron-sized particles into a flow field for analysis, and then using high-performance cameras to register their movements in real time. Instead of using synthetic particles, the DLR researchers are now using water droplets naturally available during in-flight testing. The entire flow field can be computed and visualised in three dimensions using specially developed software. Until now, it had not been possible to measure the airflow around an entire wing on a passenger aircraft under in-flight conditions. Previous systems involved the attachment of sensors to the wing surfaces; these come with the disadvantage of interfering with the airflow and are only able to perform measurements at a limited number of positions on the wing. DLR researchers conducted trials of PIV in 2009 and 2013, at that time using the DLR Do 228 research aircraft – a substantially smaller, propeller-driven aircraft.

Last modified:
12/01/2015 09:35:43

Contacts

 

Falk Dambowsky
German Aerospace Center (DLR)

Corporate Communications, Editor Aeronautics

Tel.: +49 2203 601-3959
Christina Politz
German Aerospace Center (DLR) (DLR)

Institute of Aerodynamics and Flow Technology

Tel.: +49 551 709-2462
Prof. Dr. Ralf Rudnik
German Aerospace Center (DLR)

DLR Institute of Aerodynamics and Flow Technology

Tel.: +49 531 295-2410
Hans-Jürgen Berns
German Aerospace Center (DLR)

Flight Operations, Flight Facility Braunschweig

Tel.: +49 531 295-2669

Fax: +49 531 295-2220