An experimental aero-acoustic characterisation of the NACA 63 ₃-018 airfoil is presented in this study, featuring trailing-edge noise emissions with and without serrations. Measurements have been carried out for a chord-based Reynolds number range between 0.18 × 10 ⁶ and 4.8 × 10 ⁶ . Two airfoil models with different chord lengths have been tested in five different wind tunnels. The goal is to compare the measurements in different facilities, quantify the uncertainties, and establish a validation database that can serve as a benchmark for computational studies. The tests have been performed with clean and forced-transition boundary layers for a variety of angles of attack. The effect on the spectral slope and peak levels is evaluated. Scaling laws have been applied to compare different test conditions. The quality and nature of the collapse, as well as the applicability limits of the scaling, are examined. Different serration geometries have been tested at different flap angles. The noise reduction dependence on the aerodynamic loading is discussed. This work is based on an initiative of Task 39 "Quiet Wind Turbine Technology" of the Technology Collaboration Programme (TCP) of the International Energy Agency (IEA).

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Abstract: Differential infrared thermography (DIT) is a method of analyzing infrared images to measure the unsteady motion of the laminar–turbulent transition of a boundary layer. It uses the subtraction of two infrared images taken with a short-time delay. DIT is a new technique which already demonstrated its validity in applications related to the unsteady aerodynamics of helicopter rotors in forward flight. The current study investigates a pitch-oscillating airfoil and proposes several optimizations of the original concept. These include the extension of DIT to steady test cases, a temperature compensation for long-term measurements, and a discussion of the proper infrared image separation distance. The current results also provide a deeper insight into the working principles of the technique. The results compare well to reference data acquired by unsteady pressure transducers, but at least for the current setup DIT results in an additional measurement-related lag for relevant pitching frequencies. Graphical abstract: [Figure not available: see fulltext.]

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Differential infrared thermography (DIT) is a method of analyzing infrared images to measure the unsteady motion of the laminar–turbulent transition of a boundary layer. It uses the subtraction of two infrared images taken with a short time delay. DIT is a new technique which already demonstrated its validity in applications related to the unsteady aerodynamics of helicopter rotors in forward 2ight. The current study investigates a pitch–oscillating airfoil and proposes several optimizations of the original concept. These include the extension of DIT to steady test cases, a temperature compensation for long–term measurements, and a discussion of the proper infrared image separation distance. The current results also provide a deeper insight into the working principles of the technique. The results compare well to reference data acquired by unsteady pressure transducers, but at least for the current setup DIT results in an additional measurement–related lag for relevant pitching frequencies.@en