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Zoppini, G. (author), Westerbeek, S.H.J. (author), Ragni, D. (author), Kotsonis, M. (author)The effect of discrete roughness elements on the development and breakdown of stationary crossflow instability on a swept wing is explored. Receptivity to various element heights and chordwise locations is explored using a combination of experimental and theoretical tools. Forcing configurations, determined based on linear stability...journal article 2022
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Gutiérrez, R. (author), Llorente, E. (author), Ragni, D. (author)The mid-span region of wind turbine blades can be thickened to fulfil the structural requirements of the blade. Hence, thick airfoils, that were designed to operate at the root region of the blade, are moved to the mid-span region. This could not imply remarkable variations of the blade performance once its surface is smooth. However, the...journal article 2022
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Nederlof, R. (author), Ragni, D. (author), Sinnige, T. (author)The use of electric motors enables a more flexible operation of propellers compared to conventional combustion engines. One possible benefit is the easier operation at negative thrust, which could be beneficial for energy recovery, control purposes, and lower noise through steeper descents. By changing the pitch of the propellers and actively...conference paper 2022
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Zoppini, G. (author), Ragni, D. (author), Kotsonis, M. (author)The present work is dedicated to the investigation of the effect of an isolated roughness element on a swept wing boundary layer. In particular, the flow modifications incurred by a single cylindrical element applied on a swept wing model are measured, toward describing the nature of the perturbations introduced in the flow field, their...journal article 2022
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Zoppini, G. (author), Michelis, Theodorus (author), Ragni, D. (author), Kotsonis, M. (author)The presented work introduces a cancellation technique, based on the linear superposition of stationary crossflow instabilities (CFIs) through the application of a streamwise series of optimally positioned discrete roughness element (DRE) arrays on a swept wing surface. The DRE arrays are designed and arranged with suitable amplitude and...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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Casalino, D. (author), Grande, E. (author), Romani, G. (author), Ragni, D. (author), Avallone, F. (author)Experimental and numerical results of a propeller of 0.3 m diameter operated at 5000 RPM and axial velocity ranging from 0 to 20 m/s and advance ratio ranging from 0 to 0.8 are presented as a preliminary step towards the definition of a benchmark configuration for low Reynolds number propeller aeroacoustics. The corresponding rotational tip...journal article 2021
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Romani, G. (author), Grande, E. (author), Avallone, F. (author), Ragni, D. (author), Casalino, D. (author)This paper proposes a CFD/CAA-based approach to predict the aerodynamic performances and tonal/broadband noise radiation of low-Reynolds number propellers at engineering level. Broadband self-noise prediction of low-Reynolds number propellers is particularly challenging, due to the requirement for the employed computational method to emulate...journal article 2021
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de Vries, R. (author), van Arnhem, N. (author), Avallone, F. (author), Ragni, D. (author), Vos, Roelof (author), Eitelberg, G. (author), Veldhuis, L.L.M. (author)This experimental study focuses on the aerodynamic interaction between an over-the-wing (OTW) propeller and a wing boundary layer. An OTW propeller is positioned above the hinge line of a wing with a trailing-edge flap. Measurements are carried out with and without axial pressure gradients by deflecting the flap and by extending the flat upper...journal article 2021
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Zoppini, G. (author), Ragni, D. (author), Kotsonis, M. (author)An experimental parametric study of the effect of discrete roughness elements (DRE) on the development and breakdown of stationary crossflow instability on a swept wing is presented. A systematic investigation of the receptivity to various elements height and chord locations is carried out in a crossflow dominated flow. The flow is globally and...conference paper 2021
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Teruna, C. (author), Avallone, F. (author), Ragni, D. (author), Rubio Carpio, A. (author), Casalino, D. (author)Lattice Boltzmann simulations were carried out to investigate the noise mitigation mechanisms of a 3-D printed porous trailing-edge insert, elucidating the link between noise reduction and material permeability. The porous insert is based on a unit cell resembling a lattice of diamond atoms. It replaces the last 20 % chord of a NACA 0018 at...journal article 2021
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Tamaro, Simone (author), Zamponi, R. (author), Ragni, D. (author), Teruna, C. (author), Schram, Christophe (author)Abstract: The flow field on solid and porous airfoils subjected to turbulence shed by an upstream cylindrical rod and the corresponding far-field noise radiations are studied through particle image velocimetry (PIV) and microphone measurements, respectively. Three different Reynolds numbers based on the rod diameter are considered in a range...journal article 2021
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Teruna, C. (author), Avallone, F. (author), Ragni, D. (author), Casalino, D. (author), Rubio Carpio, A. (author)This manuscript presents a numerical investigation of an open-cell 3D-printed perme-able/porous insert used to reduce turbulent boundary layer-trailing edge (TBL-TE) noise. The matrix topology of the insert resembles the lattice of diamond atoms, and thus, it is also referred to as the diamond trailing edge (TE). The porous insert replaces...conference paper 2021
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Arcondoulis, Elias J. G. (author), Liu, Yu (author), Yang, Yannian (author), Ragni, D. (author), Rubio Carpio, A. (author), Avallone, F. (author)View Video Presentation: https://doi-org.tudelft.idm.oclc.org/10.2514/6.2021-2226.vid<br/><br/>The mechanisms responsible for vortex shedding reduction, due to the application of a porous coating to a smooth cylinder placed in uniform flow, are still uncertain despite several numerical and experimental studies. To help understand these...conference paper 2021
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Zamponi, R. (author), Schram, C (author), Moreau, S. (author), Ragni, D. (author)View Video Presentation: https://doi-org.tudelft.idm.oclc.org/10.2514/6.2021-2289.vid<br/><br/>A possible strategy for the reduction of the aeroacoustic noise generated by turbulence interacting with a wing profile, also referred to as leading-edge noise, is represented by the implementation of a porous medium in the structure of the airfoil....conference paper 2021
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Lima Pereira, L.T. (author), Avallone, F. (author), Ragni, D. (author)iew Video Presentation: https://doi-org.tudelft.idm.oclc.org/10.2514/6.2021-2179.vid<br/><br/>The unsteady surface pressure fluctuations over trailing-edge serrations retrofitted to the benchmark NACA 633-018 profile are experimentally measured. Miniaturized unsteady pressure transducers installed on the serration surface are used to describe...conference paper 2021
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Teruna, C. (author), Avallone, F. (author), Casalino, D. (author), Ragni, D. (author)A lattice-Boltzmann method has been employed to study the aeroacoustics and aerodynamics of airfoils equipped with leading edge treatments, namely the porous leading edge and leading edge serrations. The present study aims to identify the differences in noise reduction mechanisms between the two treatments. Within the context of...journal article 2021
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Ye, Q. (author), Avallone, F. (author), Ragni, D. (author), Choudhari, Meelan (author), Casalino, D. (author)Surface roughness elements are often used to force laminar to turbulent transition in aerodynamic and aeroacoustic wind-tunnel experiments. The statistical features and spectral content of the pressure fluctuations in the resulting turbulent boundary layer at the trailing edge can affect far-field noise. To elucidate this dependence, boundary...journal article 2021
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Teruna, C. (author), Avallone, F. (author), Ragni, D. (author), Casalino, D. (author)Numerical simulations, using a lattice-Boltzmann technique, have been carried out to study the effect of aerodynamic loading and Reynolds number on the aeroacoustics of a porous trailing-edge insert. The airfoil is a National Advisory Committee for Aeronautics 0018 with the last 20% of its chord being replaceable with porous insert based on a...journal article 2021
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Candeloro, Paolo (author), Nargi, Ranieri Emanuele (author), Grande, E. (author), Ragni, D. (author), Pagliaroli, Tiziano (author)The present study reports an experimental investigation regarding one of the most effective and most studied passive control technique in literature to mitigate the noise pollution radiating by a small drone: the Serrated Trailing Edge (STE). 23 quiet propellers have been designed and manufactured in order to identify the most silent...journal article 2021