No abstract

Recent research confirmed leading edge serrations to be an effective passive noise reduction treatment for aerofoil broadband noise at high-turbulent inflow conditions. Therefore, reducing leading edge broadband noise while maintaining acceptable aerodynamic aerofoil performance represents a pressing task for future applications. In this context, an extensive aeroacoustic study, analysing a NACA65(12)-10 aerofoil, was continued towards defining an aeroacoustic optimum between aerofoil noise radiation and noise reduction due to serrated leading edges in order to provide ideal design parameters for low-noise serrations. On this basis, part of the aeroacoustically analysed experimental space was extracted and analysed in terms of aerodynamic performance parameters, defined by lift and drag coefficients. This was carried out both, numerically and experimentally. The main parameters of interest were a variation of the Reynolds number, the angle of attack and the serration design parameters, namely the serration amplitude and the serration wavelength. The aerodynamic study showed a good match between experimental and numerical results in the pre-stall regime. Slight deviations occurred in a precise determination of the stall-angle and the maximum lift coefficients which mainly could be assigned to differing boundary conditions. However, for the serrations slight improvements of the maximum pre-stall angles as well as high post-stall lift coefficients were observed, which could be linked to specific separation pattern on the aerofoil suction side. An increase of the serration wavelength showed an increased lift performance, which could not be linked solely to a change in the aerofoils surface. Combining aeroacoustic and aerodynamic results showed that the aerodynamic trends towards a maximum lift performance compete aeroacoustic maximum-performance findings. Finally, defining a polyoptimum of the multi-parameter system in terms of maximum noise reduction effects while maintaining an acceptable aerodynamic performance provides a deepened insight into the relations between aerodynamics and aeroacoustics, where the presented data pool might give assistance for future design processes.

This paper presents experimental results on the aeroacoustic performances of a NACA 65(12)-10 aerofoil subjected to serrated leading edges. The serration patterns of these leading edges are formed by cutting into the main body of the aerofoil, instead of extending the leading edges. Therefore these serrated leading edges, when attached to the main body of the aerofoil, will always result in the same overall chord length. The experiment was performed in an aeroacoustic wind tunnel facility. These serrated leading edges were investigated for their effectiveness in suppressing four different types of noise sources: laminar instability tonal noise, leading edge separation bubble noise, turbulence-leading edge interaction noise and trailing edge self-noise. Streamwise vortices produced by an optimised serrated leading edge can suppress the separation bubble at the trailing edge, thereby reducing the instability laminar tonal noise significantly. It is found that the most effective serration configuration is the one with the largest serration amplitude and smallest serration wavelength. Without even relying on the streamwise vortices, the sawtooth geometry of the serration itself can already be sufficient to suppress the leading edge separation bubble. Due to the special geometry of the NACA 65(12)-10, it is very effective in the production of laminar separation bubble noise at the leading edge. The use of serrated leading edge can therefore be an effective passive device to suppress this particular noise source. Similarly, the most effective serration geometry in the reduction of turbulenceleading edge interaction noise is the one with the largest serration amplitude and smallest serration wavelength. However, this configuration is also prone to generating superfluous noise at high frequency. Extensive boundary layer and very near wake measurements were performed to investigate the flow structures on the NACA 65(12)-10 aerofoil with a large serration amplitude leading edge. It can be concluded that the serrated leading edge is very disruptive to the hydrodynamic growth of the turbulent boundary layer at the trailing edge. Evidences on the reduction of boundary layer low-frequency turbulence at the trailing edge could support the hypothesis of a reduction in the low-frequency far field noise. This remains to be confirmed in the future studies.

Measurement of magnetic fieldMagnetic field in electromagnetism a b s t r a c t A method is proposed for calibrating the radius of a rotating coil sensor by relaxing the metrological constraints on alignment and field errors of the reference quadrupole. A coil radius calibration considering a roll-angle misalignment of the measurement bench, the magnet, and the motor-drive unit is analyzed. Then, the error arising from higher-order harmonic field imperfections in the reference quadrupole is assessed. The method is validated by numerical field computation for both the higher-order harmonic errors and the roll-angle misalignment. Finally, an experimental proof-of-principle demonstration is carried out in a calibration magnet with sextupole harmonic.

Die Entwicklung neuer mobiler Systeme wird weiterhin Fortschritte in der Verpackungstechnik von integrierten Schaltungen bewirken und die eingesparte Fläche ermöglicht zusätzliche Produkteigenschaften, welche sich verkaufsfördernd auswirken. So finden sich beispielsweise Höhenmesser und Barometer bereits heute in Uhren und Taschenmessern wieder. Hierzu werden Drucksensoren von hoher Genauigkeit und mit möglichst kleinem Formfaktor herangezogen, d. h. im Idealfall vollständig kalibrierte Drucksensoren für die Flip-Chip-Montage. Für solche Bauelemente sind neue Methoden für die notwendige Kalibrierung zu entwickeln. Im Folgenden wird ein Verfahren für die Kalibrierung von integrierten Drucksensoren im Waferverbund vorgestellt, das am FhG-IMS Duisburg Einsatz findet.