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Mourão Bento, H.F. (author), VanDercreek, Colin (author), Avallone, F. (author), Ragni, D. (author), Sijtsma, P. (author), Snellen, M. (author)Aeroacoustic tests in closed wind tunnels are affected by reflections in the tunnel circuit and background noise. Reflections can be mitigated by lining the tunnel circuit. The present study investigates if lining exclusively the most accessible segment of a closed wind tunnel circuit, in particular the test section, is an approach which...conference paper 2023
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Luesutthiviboon, S. (author), Meirelles Pereira, L. (author), Ragni, D. (author), Avallone, F. (author), Snellen, M. (author)The authors would like to provide the following corrections and clarifications to the article titled “Aeroacoustic Benchmarking of Trailing-edge Noise from a NACA 633–018 Airfoil with Trailing-edge Serrations” which has been published in the AIAA Journal Vol. 61, No. 1, and can be accessed online via https://doi.org/10.2514/1.J061630. The first...journal article 2023
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Luesutthiviboon, S. (author), Lima Pereira, L.T. (author), Ragni, D. (author), Avallone, F. (author), Snellen, M. (author)Experimental results on trailing-edge (TE) noise from a NACA 63<sub>3</sub> –018 airfoil are presented for a chord-based Reynolds number Re<sub>c</sub> range between 2 × 10<sup>5</sup> and 3 × 10<sup>6</sup>. Far-field TE noise from the baseline airfoil with a straight TE and TE serrations is measured with varying Re<sub>c</sub>, angle of...journal article 2023
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Mourão Bento, H.F. (author), VanDercreek, Colin (author), Avallone, F. (author), Ragni, D. (author), Snellen, M. (author)Microphone measurements in a closed test section wind tunnel are affected by turbulent boundary layer (TBL) pressure fluctuations. These fluctuations are mitigated by placing the microphones at the bottom of cavities, usually covered with a thin, acoustically transparent material. Prior experiments showed that the cavity geometry affects the...journal article 2022
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VanDercreek, Colin (author), Avallone, F. (author), Ragni, D. (author), Snellen, M. (author)Cavities placed along wind tunnel walls can attenuate the turbulent boundary layer (TBL) fluctuations as they propagate into the cavity. Placing microphones within the cavities can thus improve the signal-to-noise ratio of acoustic data. However, standing waves form within these cavities distorting the acoustic measurements. This work uses a...journal article 2022
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Mourão Bento, H.F. (author), Ragni, D. (author), Avallone, F. (author), Simons, D.G. (author), Snellen, M. (author)Sound absorbing porous materials are used to line a wind tunnel wall, in order to reduce reflections. However, the lining can have a detrimental effect on the acoustic measurements due to an increase in the noise radiated from the walls. In addition, the aerodynamic fidelity of the tunnel can be affected. In the present study, the influence...journal article 2022
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Luesutthiviboon, S. (author), Ragni, D. (author), Avallone, F. (author), Snellen, M. (author)This study focuses upon a new permeable topology design concept as an alternative to porous metal foams, for turbulent boundary layer trailing-edge (TBL-TE) noise attenuation. The present permeable topology has unconventional characteristics with respect to the metal foams: a combination of low flow resistivity r and high form drag...journal article 2021
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Lima Pereira, L.T. (author), Merino Martinez, R. (author), Ragni, D. (author), Gómez-Ariza, David (author), Snellen, M. (author)This paper explores the advantages of combining asynchronous microphone array measurements for acoustic source mapping in two and three–dimensional applications. Four different approaches are considered, three consisting of the combination of the source maps (arithmetic mean, geometric mean, and minimum value), and a fourth one obtained by...journal article 2021
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Rubio Carpio, A. (author), Avallone, F. (author), Ragni, D. (author), Snellen, M. (author), van der Zwaag, S. (author)An experimental study on broadband noise scattered by permeable trailing edges with different pore arrangements is performed. A NACA 0018 airfoil with chord c = 0.2 m is investigated at chord-based Reynolds numbers ranging from 1.4 × 10<sup>5</sup> to 3.8 × 10<sup>5</sup> and angles of attack of 0.2 and 5.4 degrees. Noise emission from five...journal article 2020
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Merino Martinez, R. (author), Luesutthiviboon, S. (author), Zamponi, R. (author), Rubio Carpio, A. (author), Ragni, D. (author), Sijtsma, P. (author), Snellen, M. (author), Schram, Christophe (author)In this paper, the performance of four acoustic imaging methods: conventional frequency domain beamforming (CFDBF), functional beamforming (FUNBF), enhanced high resolution CLEAN–SC (EHR–CLEAN–SC) and generalized inverse beamforming (GIBF), is investigated in terms of accuracy and variability. Three experimental test cases are considered: 1)...journal article 2020
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VanDercreek, Colin (author), Merino Martinez, R. (author), Snellen, M. (author), Ragni, D. (author), Simons, D.G. (author)This paper analyses the influence of microphone cavity geometry on beamforming measurements with a turbulent boundary layer present on the microphone array. A 16- microphone array was tested in the anechoic open-jet wind tunnel of the Delft University of Technology. The array was placed on a flat plate mounted flush with the exit nozzle of the...conference paper 2020
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VanDercreek, Colin (author), Amiri Simkooei, A. (author), Snellen, M. (author), Ragni, D. (author)This study investigates how embedding microphones in different cavity geometries along the wall of a wind tunnel reduces the measured turbulent boundary layer pressure fluctuations. The effect of these cavities on the measured signal-to-noise ratio of an acoustic source with flow present was also quantified. Twelve cavity geometries defined...journal article 2019
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Rubio Carpio, A. (author), Avallone, F. (author), Ragni, D. (author), Snellen, M. (author), van der Zwaag, S. (author)The turbulent flow over a porous trailing edge of a NACA 0018 airfoil is experimentally investigated to study the link between the hydrodynamic flow field and the acoustic scattering. Four porous trailing edges, obtained from open-cell metal foams, are tested to analyze the effects on far-field noise of the permeability of the material and of...journal article 2019
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Rubio Carpio, A. (author), Merino Martinez, R. (author), Avallone, F. (author), Ragni, D. (author), Snellen, M. (author), van der Zwaag, S. (author)The hydrodynamic and acoustic fields for a NACA 0018 with solid and porous trailing edge inserts are investigated. The porous inserts, covering 20% of the chord, are manufactured with metal foams with cell diameters of 450 and 800 μm and permeability values of 6 × 10−10 and 2.7 × 10−9 m2. The experiments are performed at a chord-based Reynolds...journal article 2019
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VanDercreek, Colin (author), Manjunath, P. (author), Ragni, D. (author), Snellen, M. (author)This study investigated how embedding microphones in different cavity geometries reduce the measured turbulent boundary layer pressure fluctuations at the microphones. The cavity geometries were systematically varied using a design of experiments (DOE) methodology. This approach tested different cavity depths, diameters, chamfers, and opening...conference paper 2019
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Rubio Carpio, A. (author), Avallone, F. (author), Ragni, D. (author), Snellen, M. (author), van der Zwaag, S. (author)Turbulent boundary layer trailing-edge noise scattered by a NACA0018 airfoil equipped with 3D printed perforated trailing-edge inserts, i.e. with straight cylindrical channels connecting the two sides of the airfoil, is investigated. The inserts have different permeability in order to assess the effect of this property on broadband noise...conference paper 2019
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VanDercreek, Colin (author), Sijtsma, P. (author), Snellen, M. (author), Ragni, D. (author), Avallone, F. (author), Simons, D.G. (author)A mathematical model is proposed that evaluates acoustic propagation of turbulent boundary layer waves on top of a cavity enclosing a microphone. The goal is to optimize these cavity geometries to improve the signal-to-noise ratio of acoustic measurements. This model predicts the attenuation of the turbulent boundary layer fluctuations...conference paper 2019
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Luesutthiviboon, S. (author), Avallone, F. (author), Ragni, D. (author), Snellen, M. (author)An analytical method for predicting the steady pressure distribution on porous airfoils with a prescribed porosity distribution is assessed through comparison of its lift prediction with experimental data. The method is based on the thin-airfoil formulation. The no-slip boundary condition of the airfoil surface has been replaced by the Darcy’s...conference paper 2019
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Manjunath, P. (author), Avallone, F. (author), Casalino, D. (author), Ragni, D. (author), Snellen, M. (author)Acoustic liners are widely used as noise suppression devices, for example in aircraft engines. The effectiveness of the liners is measured through the impedance. In the present study, using a lattice-Boltzmann solver, the response of two liner geometries to grazing acoustic waves is examined. The two geometries have porosity equal to 0.99%...conference paper 2018
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Merino Martinez, R. (author), Sanders, Martinus P.J. (author), Caldas, Luciano C. (author), Avallone, F. (author), Ragni, D. (author), de Santana, Leandro D. (author), Snellen, M. (author), Simons, D.G. (author)Microphone arrays are useful measurement devices for estimating the location and strength of sound sources. Numerous comparative studies have been conducted regarding the performance of acoustic imaging methods in the past, but literature lacks of a systematic investigation on the role of the hardware on the measurements. This research...conference paper 2018
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