Large-Scale Slat Noise Studies within the Project OPENAIR

Abstract

The present contribution summarizes the slat noise research activity within work package WP4.2 (Wing Systems) of the EC co-financed project OPENAIR (Optimisation for low environmental noise impact aircraft) conducted by the partners Airbus and DLR. It involves both experimental and numerical studies at the large-scale (1:3.3) swept high-lift wing model F15-LS. Experiments were performed in the Large Low-speed Facility DNW-LLF • to extend current slat noise validation data bases towards more realistic test conditions than in precursor projects to support the further development of DLR’s numerical slat noise prediction capability and • to verify the documented noise reduction benefit of established slat noise reduction concepts from precursor projects for these extended test conditions. Slat noise reduction concepts that have been revisited and further developed were • optimized slat gap and overlap settings as well as • an adaptive slat concept that actively reduces the gap width to reduce noise under typical approach conditions but restores the original gap width / maximum lift if necessary. OPENAIR slat noise studies build upon the outcome of the forerunner project TIMPAN, where the noise differences attributed to slat setting variations were numerically predicted and experimentally validated at a fourfold smaller 1:13.2-scaled 2D high-lift system (F16 model). FEM analysis served to specify technically feasible adaptive slat profile bending, accounting for conventional actuator specifications, feasible skin materials and critical aerodynamic loads determined by the flight envelope. Two selected adaptive slat shapes were finally realized as solid model parts that were tested in the DNW-LLF (fully closed gap, intermediate gap width). Main results were: The adaptive slat with closed gap provides a noise reduction of order 5 dB at wing level, equivalent to a full elimination of the slat noise source. Modified slat settings or an adaptive slat with intermediate gap width are suited to reduce slat noise by about 2─3 dB at wing level while producing negligible aerodynamic impact at the operative test angles of attack. Comparisons of CAA (Computational Aeroacoustics) prediction results with the DNW-LLF measurement data revealed a generally good reproduction of the observed trends with the restriction that measured differences to be resolved were relatively small for most of the tested slat setting variants. Overall, major results from the TIMPAN project were reproduced within OPENAIR. Particularly, the expectation of a relatively broad optimum for aeroacoustically optimized slat settings, as deduced from the former TIMPAN results, is supported by both the measurement and CAA results.