Phased microphone arrays have become a well-established tool for performing aeroacoustic measurements in wind tunnels (both open-jet and closed-section), flying aircraft, and engine test beds. This paper provides a review of the most wellknown and state-of-the-art acoustic imaging methods and recommendations on when to use them. Several exemplary results showing the performance of most methods in aeroacoustic applications are included. This manuscript provides a general introduction to aeroacoustic measurements for non-experienced microphone-array users as well as a broad overview for general aeroacoustic experts.

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The noise reduction potential of trailing edge serrations in a linear cascade of seven loaded airfoils is investigated experimentally for Re= 5.5 × 10 5 and M= 0.23. Turbulent boundary layer trailing edge noise is considerably reduced in the low-to mid-frequency range similarly to previous isolated airfoil investigations. A high frequency noise increase is also found for St= fδ/U > 1.2. The cascade effect is neither found to enhance nor to limit the noise reduction of serrations, except in the very low frequency range where the noise reduction potential found for isolated airfoils is not recovered. The loading of the airfoil is not affected by the serrations but the drag is increased by 14%. High speed particle image velocimetry is carried out in the near wake of a serration tooth and compared to the straight edge. The suction side turbulent boundary layer is nearly suppressed from the airfoil surface which might partly explain the observed noise reduction. Conversely the pressure side boundary layer turbulence crosses the troughs of the serrations. A third turbulent region generated at the very trailing edge is identified as a consequence of the Kutta condition. The elongated geometry of the sawtooth serrations makes it vanish faster with the downstream distance than in the straight edge case. Nomenclature b [m] Half-chord (= c/2) s [m] Blade pitch λ [m] Serration wavelength h [m] Amplitude of the serrations ω [rad.s − 1] Acoustic puslation, St Strouhal number δ [m] Boundary layer thickness, m δ * [m] Boundary layer displacement thickness, m θ * [m] Boundary layer momentum thickness, m α c [deg] Geometrical angle of attack β c [deg] Air inlet angle U [m.s −1 ] Mean flow velocity ρ [kg.m −3 ] Fluid density C p Pressure Coefficient C D Drag Coefficient σ = c/s Cascade solidity Subscripts 1 Upstream quantities * PhD Student2 Downstream quantities p Pressure side quantities s Suction side quantities Superscripts a Mean quantities a ′ Fluctuating quantities

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Abstract. A wind turbine blade equipped with root spoilers is analysed using 2D Computational Fluid Dynamics (CFD) to assess the unsteady impact of passive devices. Several metrics such as lift and drag coefficients, pressure and instantaneous velocity field around the aerofoil, Power Spectral Density and Strouhal number are used in the 2D unsteady analysis. The spoiler is found to efficiently rearrange the flow, adding lift throughout the positive angles of attack. However, the drawback is a high drag penalty coupled with high unsteadiness of the aerodynamic forces.