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 × 10 6 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 efficient: 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.
This work presents first results obtained with partly scale resolving simulation for two different installation noise problems involving a cold jet interacting with a wing. Similar to very large-eddy simulation (VLES), the resolvable very large scales of turbulent fluctuations are directly calculated and the dissipation of the non-resolved scales is accounted for by a subfilter scale stress model. In addition, stochastic forcing in space and time is applied to model turbulent backscatter. The paper presents and discusses the rationale to explicitly realize turbulent backscatter along with details of the proposed stochastic backscatter model and its calibration. As a novel approach, the entire subfilter forcing function is modeled by means of an eddy-relaxation source term that provides a combined model for forcing and dissipation. The relaxation parameter defines the amount of correlation of the subfilter forcing with resolved quantities. Its proper calibration is achieved using decaying homogeneous isotropic turbulence. Furthermore, characteristics of the backscatter forcing are analyzed from synthetic turbulence data. The first jet-wing interaction problem studied is based on a generic static jet interacting with a non-inclined rectangular wing. The second problem deals with a dual-stream nozzle installed at a high-lift wing with deployed flap and slat in wind tunnel flow under approach conditions. For both problems installation noise from the airframe yields higher peak levels than the jet-noise contribution alone. For the first problem, relative to the corresponding jet spectrum a low-frequency narrow-band contribution is observed that can be attributed to coherent jet structures interacting with the airfoil trailing edge. Very good agreement with measured spectra is obtained. For the second problem a broadband airframe installation contribution to the overall spectrum is predicted with peak frequency above the jet contribution.
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