DLR studies wing-flap aerodynamics

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European researchers are conducting flight and windtunnel tests to improve aerodynamic modelling for wing flaps and slats.

Specialists at the European Transonic Wind Tunnel (ETW) in Cologne have performed scale-model tests in extreme sub-zero temperatures down to -160°C (-256°F) to generate data in unprecedented detail about the aerodynamic conditions around the high-lift devices, says German aerospace centre DLR.

The research institute is part of a joint project dubbed “High lift In-flight Validation” (INVA) together with Airbus, Berlin’s technical university and ETW in an initiative that is part-funded by Germany’s ministry for economic affairs and energy.

The objective is to predict more precisely the aerodynamic processes on the wing during take-off and landing by determining variations between computational fluid dynamic models and real data from windtunnel and flight tests.

DLR conducted 10 test flights with its Airbus A320-based “Advanced Technology Research Aircraft” (ATRA) in Toulouse in June 2012, including stall flights in landing configuration. That data has informed design of a high-precision model A320 wing specifically made for the INVA project’s windtunnel tests.

The researchers employed laser-based particle image velocimetry to observe the development of vortices and airflow separation on the windtunnel model. The technology allows measurement of flow velocities in “many critical areas” of the wing at the same time, says project co-ordinator Ralf Rudnik. “Therein lies one of the keys to acquire a better understanding of where and why lift breaks down,” he adds.

This is the first time that DLR has studied the high-lift devices in such detail. Aside from the flaps and slats, the shape and size of the gaps between the retractable aerofoils and main wing are crucial to the overall effectiveness of the high-lift system.

Simulation of the complex processes involved in the wing generating maximum lift especially at the edges of the flight envelope is still a major challenge for today’s computational models, says DLR. “To further improve the models, we urgently need real flow data from in-flight and windtunnel tests,adds Cord-Christian Rossow, head of DLRs institute of aerodynamics and flow technology in Braunschweig.

More test flights are planned for the autumn of 2014. ATRA is to be equipped with PIV technology to measure airflow speeds across the wing and high-lift devices.

For the cryogenic windtunnel tests, the researchers employed nitrogen as flow medium and increased the atmospheric pressure inside the ETW by a factor of 3.3. Some 1,281t of liquid nitrogen was thus evaporated and fed into the windtunnel.