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Fiscaletti, D. (author), Lima Pereira, L.T. (author), Ragni, D. (author)The present study focuses on the application of finlet rails as a passive technique of flow control to mitigate trailing-edge noise. Finlet rails are small cylinders whose axes are aligned along the streamwise direction, transversally positioned with respect to the trailing edge. In the first part of this study, the effects of finlet geometry...journal article 2024
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Baars, W.J. (author), Ragni, D. (author)Rotor noise comprises harmonic features, related to the blade passing frequency, as well as broadband noise. Even though acoustic spectra yield frequency-distributions of acoustic energy within pressure time series, they do not reveal phase-relations between different frequency components. The latter are of critical importance for the...conference paper 2023
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Kalyani, S.K. (author), Jaiswal, P. (author), Rendón, Jose (author), Moreau, Stéphane (author), Ragni, D. (author)The present experimental investigation focuses on a flow-field and noise characterization of a CD airfoil experiencing large flow separation and stall. Measurements are performed to investigate the effect of Reynolds number stalling noise signature of the CD airfoil. This study includes investigation of the potential interaction of wind tunnel...conference paper 2023
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Boatto, U. (author), Bonnet, Jean-Paul (author), Avallone, F. (author), Ragni, D. (author)The design of efficient rotor blades is affected by the accuracy of aerodynamic prediction methods for load distributions and power computations. Research showed that the accuracy of BEMT-based industrial codes decreases at high inflow-speed under uniform aligned steady conditions. The identified reasons are inaccuracies in the semi-empirical...conference paper 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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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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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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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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do Nascimento Monteiro, F. (author), Ragni, D. (author), Avallone, F. (author), Sinnige, T. (author)A low-order numerical tool for estimating noise emissions from distributed propeller configurations is presented. The paper describes the tool's computational framework, which uses Hanson's near-field theory to calculate the thickness and loading noise components. The formulation assumes steady blade loading, but an unsteady case can be handled...conference paper 2023
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Boatto, Umberto (author), Bonnet, Paul A. (author), Avallone, F. (author), Ragni, D. (author)Blade Element Momentum Theory (BEMT) -based approaches provide 15%–20% inaccurate load predictions under uniform steady inflow. Inaccuracies were related to unclear aerodynamic mechanisms causing the Prandtl Tip-Root Loss (TRL) correction to fail at high Tip-Speed Ratio (TSR) and the ambiguous drag coefficient treatment under Stall Delay (SD)...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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Lima Pereira, L.T. (author), Avallone, F. (author), Ragni, D. (author), Buck, Steven (author), Oerlemans, S. (author)This work proposes a semi-empirical framework to predict the noise of wind turbines with serrated trailing edge blades. The framework is employed for studying the reduction of the noise of the SWT 2.3-93 benchmark wind turbine. The framework is verified against field acoustic measurements of the real wind-turbine model and of noise reduction...conference paper 2023
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Avallone, F. (author), Ragni, D. (author)Noise reduction is one of the major challenges to the societal acceptance of wind turbines. Aerodynamic noise sources are the dominant ones, assuming that mechanical noise can be reduced by correct insulation and periodic maintenance of the gearbox and drive train and by adding insulating material in the wind-turbine nacelle. The dominant...book chapter 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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Terracol, Marc (author), Manueco, Lucas (author), Manoha, Eric (author), Avallone, F. (author), Ragni, D. (author), Rubio Carpio, A. (author)This study presents a numerical investigation of the noise mitigation effect provided by several fairings placed upstream of a simplified two-wheel landing gear. The chosen configuration is equipped with detachable elements that mimic realistic components, e.g. brakes and torque link, to include representative landing gear noise sources. Several...conference paper 2023
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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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Dekker, H.N.J. (author), Tuinstra, M (author), Baars, W.J. (author), Scarano, F. (author), Ragni, D. (author)A semi-emperical model is developed, able to capture the aeropropulsive performance characteristics of Over-The-Wing propellers at incidence. The model is based on an hypothesis on the interactions of the propeller- and wing-induced flow fields. Effects of these interactions on the both the thrust and lift are written in a form in which the...conference paper 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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- Dekker, H.N.J. (author), Tuinstra, Marthijn (author), Baars, W.J. (author), Scarano, F. (author), Ragni, D. (author) conference paper 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