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.

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The wall pressure fluctuations beneath a turbulent boundary layer with zero and non-zero pressure gradients were measured at a flat plate configuration in the Acoustic Windtunnel Braunschweig. The fluctuating pressure was measured by an array of subminiature pressure transducers. In addition, the mean flow velocity profiles within the turbulent boundary layer were obtained using hot wires. Adverse and favorable pressure gradients were realized by placing a rotatable NACA 0012 airfoil with a chord length of 40 cm above the flat plate. The one-point spectra and the two-point correlation properties are analysed. An empirical spectral model for the wall pressure fluctuations beneath an adverse pressure gradient boundary layer is developed based on the measured data. The effects of the pressure gradients on the characteristics of the wall pressure fluctuations are discussed.

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