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Lima Pereira, L.T. (author), Avallone, F. (author), Ragni, D. (author), Scarano, F. (author)This work discusses the physics of noise reduction achieved from serrated trailing–edges and its impact by the serration design. An experimental campaign is carried out with a benchmark 2D model based on a NACA 63<sub>3</sub>–018 airfoil. Different trailing-edge serrations are tested under several flow speeds and angles of attack conditions...journal article 2023
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Yunus, F. (author), Casalino, D. (author), Avallone, F. (author), Ragni, D. (author)Efficient calculation of urban air mobility noise footprint in a vertiport environment, considering acoustic effects of various designs, operational conditions, and environmental factors, is essential to limit the noise impact on the community at an early stage. To this purpose, the computationally efficient low-fidelity approach presented by...journal article 2023
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Arcondoulis, E.J.G. (author), Liu, Y. (author), Ragni, D. (author), Avallone, F. (author), Rubio Carpio, A. (author), Sedaghatizadeh, N. (author), Yang, Y. (author), Li, Z. (author)Vortex shedding in the wake of a cylinder in uniform flow can be suppressed via the application of a porous coating; however, the suppression mechanism is not fully understood. The internal flow field of a porous coated cylinder (PCC) can provide a deeper understanding of how the flow within the porous medium affects the wake development. A...journal article 2023
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Gutiérrez, R. (author), Zamponi, R. (author), Ragni, D. (author), Llorente, Elena (author), Aranguren, Patricia (author)Modern wind turbines employ thick airfoils in the outer region of the blade with strong adverse pressure gradients and high sensitivity to flow separation, which can be anticipated by leading-edge roughness. However, Reynolds average Navier-Stokes simulations currently overpredict the Reynolds shear stresses near the surface, and the flow...journal article 2023
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Luesutthiviboon, S. (author), Meirelles Pereira, L. (author), Ragni, D. (author), Avallone, F. (author), Snellen, M. (author)Correction Notice 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...journal article 2023
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Meloni, S. (author), de Paola, E. (author), Grande, E. (author), Ragni, D. (author), Stoica, L. G. (author), Di Marco, A. (author), Camussi, R. (author)Propeller noise generally exhibits a rich mixture of tonal and broadband components related to different physical mechanisms. Specifically, the tones are characterized by having deterministic and persistent characteristics, while the broadband counterpart has random behaviour. The separation is essential for the experimenters as they provide...journal article 2023
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Dekker, H.N.J. (author), Baars, W.J. (author), Scarano, F. (author), Tuinstra, Marthijn (author), Ragni, D. (author)The unsteady flow behaviour of two side-by-side rotors in ground proximity is experimentally investigated. The rotors induce a velocity distribution interacting with the ground causing the radial expansion of the rotor wakes. In between the rotors, an interaction of the two wakes takes place, resulting in an upward flow similar to a fountain....journal article 2023
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Yunus, F. (author), Casalino, D. (author), Avallone, F. (author), Ragni, D. (author)This paper presents a noise propagation approach based on the Gaussian beam tracing (GBT) method that accounts for multiple reflections over three-dimensional terrain topology and atmospheric refraction due to horizontal and vertical variability in wind velocity. A semi-empirical formulation is derived to reduce truncation error in the beam...journal article 2023
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Zoppini, G. (author), Michelis, Theodorus (author), Ragni, D. (author), Kotsonis, M. (author)This work presents the first experimental characterization of the flow field in the vicinity of periodically spaced discrete roughness elements (DRE) in a swept wing boundary layer. The time-averaged velocity fields are acquired in a volumetric domain by high-resolution dual-pulse tomographic particle tracking velocimetry. Investigation of...journal article 2023
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Romani, G. (author), Grande, E. (author), Avallone, F. (author), Ragni, D. (author), Casalino, D. (author)This paper presents a computational study of flow incidence effects on the aeroacoustics of a propeller operating at low blade-tip Mach numbers. The numerical flow solution is obtained by using the Lattice-Boltzmann/Very Large Eddy Simulation method, while far-field noise is computed through the Ffowcs-Williams & Hawkings' acoustic...journal article 2022
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Grande, E. (author), Romani, G. (author), Ragni, D. (author), Avallone, F. (author), Casalino, D. (author)This paper presents an experimental investigation of a propeller operating at low Reynolds numbers and provides insights into the role of aerodynamic flow features on both propeller performances and noise generation. A propeller operating at a tip Reynolds number regime of 4.3 × 10<sup>4</sup> − 4.38 × 10<sup>4</sup> is tested in an anechoic...journal article 2022
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Yunus, F. (author), Casalino, D. (author), Avallone, F. (author), Ragni, D. (author)This work presents a novel noise propagation approach based on the Gaussian Beam Tracing (GBT) method that accounts for complex source directivity, weather conditions, and irregular ground topology for the evaluation of the noise footprint. The approach takes a precomputed noise sphere as input and propagates the acoustic pressure...conference paper 2022
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Grande, E. (author), Ragni, D. (author), Avallone, F. (author), Casalino, D. (author)This paper explains the presence and relevance of noise caused by a laminar separation bubble (LSB) on a propeller operating at low-Reynolds number. Microphone measurements of a propeller with both clean and forced boundary layer transition blades are carried out in an anechoic wind tunnel by varying the propeller advance ratio J from 0 to 0...conference paper 2022
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Grande, E. (author), Ragni, D. (author), Avallone, F. (author), Casalino, D. (author)This paper explains the presence and relevance of noise caused by a laminar separation bubble (LSB) on a propeller operating at a low Reynolds number. Microphone measurements of a propeller with both clean and forced boundary-layer transition blades are carried out in an anechoic wind tunnel by varying the propeller advance ratio J from 0 to 0.6...journal article 2022
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Yunus, F. (author), Grande, E. (author), Casalino, D. (author), Avallone, F. (author), Ragni, D. (author)A noise footprint prediction framework for propeller-driven aircraft which couples an aerodynamic model and several aeroacoustic models is presented in this study. The aerodynamic model is based on the blade element momentum theory, while the aeroacoustic models are based on a time-domain compact dipole/monopole Ffowcs-Williams and Hawking's...journal article 2022
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Lima Pereira, L.T. (author), Avallone, F. (author), Ragni, D. (author), Scarano, F. (author)A physical description of the flow mechanisms that govern the distribution of the wall-pressure fluctuations over the surface of a serrated trailing edge is proposed. Three main mechanisms that define the variation of turbulent pressure fluctuations across the serrated edge are discussed and semi-empirical models are formulated accordingly....journal article 2022
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Lima Pereira, L.T. (author), Ragni, D. (author), Avallone, F. (author), Scarano, F. (author)The impact of aerodynamic loading on a serrated trailing edge is studied experimentally. Aerodynamic and acoustic measurements are conducted on a sawtooth-shaped trailing edge, retrofitted to a flat plate featuring a trailing-edge flap, and placed at incidence to the free-stream flow. The turbulent flow across the trailing edge is inspected...journal article 2022
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Gutiérrez, R. (author), Llorente, E. (author), Ragni, D. (author), Aranguren, P. (author)A computational fluid dynamics study is carried out to model the effects of distributed roughness at the airfoil leading-edge using the equivalent sand grain approach and Reynolds-averaged Navier–Stokes equations. The turbulence model k - ω-shear stress transport (SST) is selected to emulate a fully turbulent flow. Three k and ω boundary...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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Measurement techniques for aeroacoustics: From aerodynamic comparisons to aeroacoustic assimilationsRagni, D. (author), Avallone, F. (author), Casalino, D. (author)Sustainability has encouraged studies focusing on lowering the aeroacoustic impact of new aerodynamically optimized mechanical systems for several applications in wind-energy, aviation, automotive and urban air-mobility. The deployment of effective noise-reduction strategies starts with a deep understanding of the underlying mechanisms of...review 2022