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Wind tunnel testing of hybrid laminar flow

A large scale model with boundary layer suction for hybrid laminar flow (HLF) control was designed with tested in the Office National d'Etudes et de Recherches Aerospatiales (ONERA) SIMA wind tunnel.

A suction panel on the glove (main suction system (MSS) has been designed and the variable sweep angle range has been increased up to 28 degrees where high cross flow instabilities (CFI) were expected. Futhermore, a retracted Krueger flap resulting in 2 lower side chordwise gaps has been simulated by using suction in the second (Krueger gap suction (KGS)) and in a panel behind the second gap (Krueger panel suction (KPS)). Finally, suction on the wing's root has been applied in order to avoid attachment line transition (ALT) (ALT avoidance suction system (ASS)). Measurement techniques involved in the HLF test were:
pressure measurements;
infrared imaging (IR);
a wake rake mounted at the middle flap;
a boundary layer rake and CPM probes;
standard hotfilms behind as well as miniature hotfilms on the suction plate;
a special designed wind tunnel environment sensing probe (WESP) containing unsteady pressure transducers, microphones and a hot wire for correlating wind tunnel unsteady data with boundary layer data on the model.

At 28 degrees sweep and under realistic transonic conditions laminarity was gained up to the end of the HLF glove. Furthermore, at lower sweep angles the disturbance to the laminar boundary layer caused by 2 gaps of a retraced flap has been surpressed by suction, too. Advanced measurement techniques have been applied and tested, so that for future tests sensors can be chosen for any special purpose.

Reported by

Daimler-Benz Aerospace Airbus Gmbh
Kreetslag 10
21129 Hamburg
Germany
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