The AVACON project researches into over the wing mounted nacelle concepts (OWN). The advantages offered by this concept include; reduced ground noise level due to an acoustic shielding provided by the wing; possibility for higher bypass ratios for the engine due to the absence of ground clearance requirement compared to an under wing installation. Furthermore, earlier research in the field indicated a positive installation effect between the nacelle and the wing for installations where the engine is mounted close to the trailing edge of the wing. Fuselage mounted and wing mounted concepts were evaluated by partnering institution DLR, of which the fuselage mounted concept was more promising.
At IFAS a design system was developed for the design and optimization of nacelles for OWN installation for a UHBR engine. The main objective of the nacelle optimization study was to minimize the cruise drag of the aircraft. As the engine is to operate in off-design conditions as well such as take-off crosswind and high angle of attack; these were also included within the optimization tool. The design system consists of three modules: (i) 3D intake design module (ii) Airframe integration module (iii) nozzle optimization module. The intake module targeted an attached intake under off-design conditions and optimum pressure recovery during cruise condition. The airframe integration module evaluated the entire aircraft configuration with Wing-Body-Engine-Pylon (WBEP). Design of experiments was conducted to design an optimum nacelle cowl, while obtaining a deeper understanding into nacelle-airframe interference effects. The nozzle module evaluated different nozzle configurations to obtain the optimum nozzle coefficients and evaluated the interaction between nozzle configuration and airframe.
The integration study was performed for conventional long intakes and advanced short intakes. In order to ensure adequate performance for shorter intakes under off-design conditions, active flow control (AFC) concepts are being investigated.