Flow calculations for wings with high-lift devices

© Fraunhofer IBP

So-called high-lift devices (HLD), e.g. flaps and slats attached to the wings of aircrafts, provide lift during take-off and landing as well as during the climb and approaching phases. Deployment of HLD, however, has a side effect. They disturb the air flow and generate aero-acoustic noise, which surpasses engine noise during approaching and landing. Thus, the designing and optimizing of the HLD involves the assessment of noise which will be generated as well as the aero-dynamic performance. To optimize this balance already during the planning phase modern and high-performance simulation methods are used, i.e. Computational Fluid Dynamics (CFD) and Computational Aero-Acoustics (CAA).

Stationary CFD simulation is applied to assess the aero-dynamic properties of the wings equipped with HLD. Aero-dynamic properties such as lift, drag and pitching moment are calculated by integrating the surface pressure. To estimate the aero-aoustic noise a two-step method is used. The first step is Large Eddy Simulation (LES), i.e. the modelling of large air turbulences. At present, this is the most up-to-date method in the field of transient CFD simulation allowing the calculation of turbulent flow around the wing, from which time-varying pressure fluctuations on the wing can be derived on the basis of which sound radiation is determined by means of CAA simulation in a second step.

These tools allowed the investigation of new design concepts, e.g. a droop-nose configuration of the leading edge (LE) HLD, and the comparison with the undrooped configuration of the LE as well as with the KRÜGER flap (a kind of slat). According to these investigations the droop-nose LE increased lift by 12 % in comparison to the undrooped LE, whereas the sound level is 3 to 10 dB lower than the value of the KRÜGER flap. These results clearly show the potential of a low noise technology, and that is good news for all those suffering from aircraft noise.

The project is fundet by the European Union within the framework of the program "Clean Sky JTI Green regional aircraft".