Wind tunnel measurement carried out on an aircraft wing

Silent wings on short distance flights

© Fraunhofer IBP

Pressure distribution of lower wing side

© Fraunhofer IBP

Pressure distribution of upper wing side

© Fraunhofer IBP

Airflow tests of the wing with smoke generator.

The sky stretching above our heads is increasingly filled with aircrafts flying us to our next holiday or business destination. The number of takeoffs and landings, particularly of regional flights, has been constantly growing., During the takeoff, the engines produce background noise with full thrust, which is why precisely planned take-off paths are to reduce the exposure of the population to flight noise. When approaching for landing, the aircrafts arrive with throttled engines and the noise caused by the air flow at the wings and landing gear is predominant.

The design and aerodynamics of a wing have major impact on its acoustic performance, especially during landing with the flaps being extended. This is due to the gaps between wing and flaps producing air turbulences which generate a high noise emission. So why not designing landing flaps without gap to avoid this noise emission? This topic was being pursued within the frame of the EU project Clean Sky: a new wing with drooped leading edge and without gap was developed, the so-called “drooped nose”. The calculations of the aerodynamics (CFD Computational Fluid Dynamics) and sound radiation (CAA Computational Aeroacoustics) were performed at the IBP. They made evident that high lift values are achieved and that the noise production is significantly lower.

To confirm the efficiency of this innovation, an experiment was carried out. For this purpose, the new wing was produced on a scale of 1:6 and examined in different configurations in the wind tunnel. The wing was vertically positioned by means of an adapter on the force transmission points of the balance used for tests in the wind tunnel. The balance with transmission points adjustable in length and width is situated below a rotary disc allowing to turn the wing into the wind at different angles. Thus, the occurring forces could be measured and the lift and drag coefficients could be identified for the cruise flight (all flaps retracted) and for the landing approach. By means of an acoustic camera the noise and positions of the sound sources were determined. The camera recordings confirmed the expected significantly reduced sound generation: In the area of the wing leading edge the differences between retracted and extended landing flap were only marginal, which thus presents an important step forward in developing an innovative silent wing.