Systematic testing of the microstructural and aeroacoustic properties of porous metals applicable as low-noise trailing-edge (TE) treatments has been initiated within the Collaborative Research Center SFB 880-Fundamentals of High-Lift for Future Civil Aircraft. Generic TE noise experiments were performed at Re = 0.8 × 10 6 to 1.2 × 10 6 in DLR's open-jet AWB facility. Complementary flow measurements in the closed test section MUB wind-tunnel of the TU Braunschweig served to quantify the induced aerodynamic effects. The presented database forms part of an ongoing cumulative effort, combining experimental and numerical methods, to gain a deeper understanding of the prevalent TE noise reduction mechanisms. For the large variety of porous materials tested herein a clear dependence of the achieved broadband noise reduction (reaching 2-6 dB at maximum) on the flow resistivity was identified. Basic design recommendations for material resistivity and pore sizes, the latter to minimize high-frequency self-noise contributions, were deduced for low-noise TE applications. An acoustic nearfield pressure release across the porous region, adversely coupled with a loss in lift performance for porous TE replacements, appears as the major noise-reduction requirement.

This paper gives an overview about prediction capabilities and the development of noise reduction technologies appropriate to reduce high lift noise and propeller noise radiation for future low noise transport aircraft with short takeoff and landing capabilities. The work is embedded in the collaborative research centre SFB 880 in Braunschweig, Germany. Results are presented from all the acoustics related projects of SFB 880 which cover the aeroacoustic simulation of the effect of flow permeable materials, the characterization, development, manufacturing and operation of (porous) materials especially tailored to aeroacoustics, new propeller arrangements for minimum exterior noise due to acoustic shielding as well as the prediction of vibration excitation of aircraft structures, reduced by porous materials.

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