Large-Scale Studies on Slat Noise Reduction

Slat noise research activity within the EC co-financed project OPENAIR involved both experimental and numerical studies at the new large (1:3.3-scaled) swept high-lift wing model F15LS. Experiments were performed in the DNW-LLF (Large Low-speed Facility) to verify the noise reduction benefit of selected slat noise reduction concepts under more realistic test conditions than in precursor projects. Moreover, the gained test data served to extend current slat noise validation datasets towards larger Reynolds numbers, i.e. up to Re = 5.1 Mio. in the current experiment. Slat noise reduction concepts under review were 1) slat gap/overlap setting variations, and 2) an adaptive slat with the potential to reduce the gap width for noise reduction. Both concepts were proven highly e�fficient: Sealing of the gap leads to a maximum 5-dB noise reduction at wing level, equivalent to a full elimination of the slat noise source. Optimized slat settings or an adaptive slat with partially closed gap 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 within the linear polar region. When transposing these results to overall aircraft flight conditions, optimized slat settings might bring about a 0.5-EPNdB reduction of approach certification noise levels, provided all other relevant noise sources than the slat remain untreated. CAA (Computational Aeroacoustics) prediction results derived with DLR's PIANO and DISCO codes coupled with RANS-based stochastic source models revealed a generally good reproduction of the measured trends