Aerodynamic investigations of noise-reducing high-lift systems for passenger transport aircraft

Abstract: This diploma thesis captures the three-dimensional implementation of noise-reducing high-liftsystems. A parametric CAD model is developed for the FNG aircraft and different high-lift configurationsare built up. In the course of research, these configurations are designed based onformerly obtained two-dimensional results of DLR’s LEISA project featuring the design of a verylong chord slat (VLCS), whose slat shape resulted in a favourable aeroacoustic behaviour at noiserelevantapproach conditions. The high-lift systems derived in this thesis differ in the spanwisevariation of the slat geometry planform as well as in the applied high-lift settings described bygap, overlap and deflection angle.The aerodynamic performance is computed via CFD RANS simulations and the results arecompared to a reference high-lift system of the FNG aircraft, which has been designed in previousstudies. The observed CFD results are further evaluated in the reference wing section of the FNGaircraft in order to display the agreement between the implemented 3D high-lift configurationsand the 2D LEISA reference data. Besides the aerodynamic performance, aeroacoustic aspects arealso considered in this diploma thesis. By means of the obtained CFD results, indirect statementsabout the success of the 3D low-noise implementation approach are made.The geometrical concordance of the derived reference wing section of the 3D CAD model isfound in general to be very high in comparison to the 2D-optimized LEISA design wing section.With regard to the observed pressure distributions of the initial four designed high-lift systemshowever, small geometry deviations are noticed to affect the obtained pressure distributions in asignificantly unintended way. The requirements of a low-noise high-lift system are thus not metfor these high-lift configurations. In the 3D implementation, the 2D-optimized slat settings haveto be modified in order to maintain the favourable aeroacoustic behaviour of the 2D considerations.Based on a reduced slat deflection angle, a further derived 3D VLCS high-lift system isobtained to match the 2D-optimized pressure distributions in the reference wing section more accurately.A significant pressure increase at the VLCS trailing edge is noticed for this configuration,which shows the noise-reducing potential of the derived VLCS device. However, the aerodynamicdegradations obtained for the designed low-noise high-lift system are found to be too high in orderto still provide improved aeroacoustic behaviour during conditions of increased approachspeed. A 3D noise-reducing high-lift system is therefore not achieved, although the 2D-optimizedLEISA pressure distributions are well captured in the reference wing section of the implemented3D high-lift system featuring modified high-lift setting parameters.