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Raiola, Marco (author), Ragni, D. (author)The present study proposes a data-driven strategy to extract the dynamics of wave-packets from low-speed velocity field measurements. The flow field under study is a subsonic turbulent round jet at Re = 33000, measured over a 20-nozzle-diameters domain in the axial direction using low-repetition-rate planar Particle Image Velocimetry. The...conference paper 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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Teruna, C. (author), Ragni, D. (author), Avallone, F. (author), Casalino, D. (author)This manuscript presents a rod-linear cascade model for emulating rotor-stator interaction noise. The model is intended as a test platform for studying noise mitigation techniques for a turbofan fan stage, while it also extends the classical rod-airfoil configuration by considering a row of blades based on realistic geometrical details. The...journal article 2019
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Ye, Q. (author), Avallone, F. (author), Ragni, D. (author), Choudhari, Meelan (author), Casalino, D. (author)The effects of a finite, spanwise-periodic array of cylindrical roughness elements on boundary layer transition over a NACA 0012 airfoil are investigated at a chord-based Reynolds number of 1.44×10<sup>5</sup> by using hotwire anemometry and infrared thermography. Both the number and the spanwise spacing of roughness elements in the array are...conference paper 2019
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Llorente, Elena (author), Ragni, D. (author)A study of the aerodynamic performance of a NACA 643418 airfoil with trailing edge serrations is presented. For the prediction of the changes in lift due to the serration installation, an empirical law is derived that can be extended to typical cambered airfoils for wind turbine applications. The law is deduced from 2D and 3D Reynolds‐averaged...journal article 2019
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Rego, Leandro (author), Avallone, F. (author), Ragni, D. (author), Casalino, D. (author)A numerical investigation on jet-installation noise is performed using a software based on the Lattice-Boltzmann Method. A flat plate is placed in the irrotational hydrodynamic field of the jet, i.e. outside of the plume, resulting in noise increase due to the scattering of instability waves at the plate trailing edge. The configuration adopted...conference paper 2019
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Zamponi, R. (author), Ragni, D. (author), Van de Wyer, N. (author), Schram, C. (author)The present work aims at evaluating the effectiveness of the use of porous materials for reducing airfoil turbulence-impingement noise. To pursue this objective, a porous NACA-0024 profile filled with melamine foam has been designed for comparison with a solid model. The porous media constituting the airfoil has been fully characterized in...conference paper 2019
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Avallone, F. (author), van den Ende, Luc (author), Li, Q. (author), Ragni, D. (author), Casalino, D. (author), Eitelberg, G. (author), Veldhuis, L.L.M. (author)A numerical investigation of a propeller with swirl recovery vanes, for which experimental data exist, is performed. A second swirl recovery vane geometry, with shorter vanes to avoid the impingement of the propeller tip vortices, is also investigated. For the baseline swirl recovery vanes, the efficiency of the propulsive system increases by 2...journal article 2019
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Avallone, F. (author), Casalino, D. (author), Ragni, D. (author)This manuscript describes an aeroacoustic computational study on the impingement of a tractor-propeller slipstream on the leading edge of a pylon. Both the flow and acoustic fields are studied for two pylon leading edges: a solid and a flow-permeable one. The computational set-up replicates experiments performed at Delft University of...journal article 2018
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Avallone, F. (author), van der Velden, W.C.P. (author), Ragni, D. (author), Casalino, D. (author)Trailing-edge serrations are add ons retrofitted to wind-turbine blades to mitigate turbulent boundary-layer trailing-edge noise. This manuscript studies the physical mechanisms behind the noise reduction by investigating the far-field noise and the hydrodynamic flow field. A conventional sawtooth and a combed-sawtooth trailing-edge serration...journal article 2018
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Schneiders, J.F.G. (author), Avallone, F. (author), Pröbsting, S. (author), Ragni, D. (author), Scarano, F. (author)The power spectral density and coherence of temporal pressure fluctuations are obtained from low-repetition-rate tomographic PIV measurements. This is achieved by extension of recent single-snapshot pressure evaluation techniques based upon the Taylor’s hypothesis (TH) of frozen turbulence and vortex-in-cell (VIC) simulation. Finite time...journal article 2018
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Raiola, M. (author), Discetti, Stefano (author), Ianiro, A. (author), Samara, F. (author), Avallone, F. (author), Ragni, D. (author)This study focuses on an active strategy for unsteady-load control by means of a trailing-edge flap. Experiments on a 2D pitching and heaving NACA 0018 airfoil with an actuated trailing-edge flap are performed at a reduced frequency κ = 0.1 in a free-stream flow with Re = 1.3 × 10<sup>5</sup>. The model is equipped with 24 differential...journal article 2018
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González, G. (author), Ragni, D. (author), Avallone, F. (author), Schneiders, J.F.G. (author), Casalino, D. (author), Ianiro, A. (author)The analysis of the unsteady flow field of an axisymmetric subsonic jet at Reynolds numbers between 5,000 and 20,000 and computation of its unsteady pressure field is carried out from single snapshots of tomographic PIV measurements (acquisition rate 0.8 Hz). This is achieved by a recently developed pressure-evaluation technique based upon...conference paper 2018
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Rubio Carpio, A. (author), Avallone, F. (author), Ragni, D. (author)The turbulent flow over a NACA 0018 airfoil with porous trailing edge inserts and the resulting scattered turbulent-boundary-layer trailing edge noise are studied to investigate the effect of the cross-flow through the material. The experiments are performed at a chord-based Reynolds number of 2.63×10<sup>5</sup> and an angle of attack of 0°....conference paper 2018
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Li, Q. (author), Öztürk, K. (author), Ragni, D. (author), Sinnige, T. (author), Eitelberg, G. (author), Veldhuis, L.L.M. (author), Yangang, Wang (author)The momentum transferred to the fluid by a running propeller contains not only the desired axial component but also a rotational component that does not contribute to the propeller thrust. By introducing a set of swirl-recovery vanes (SRVs) downstream of the propeller, part of the rotational flow in the slipstream can be redirected into the...journal article 2018
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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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Sinnige, T. (author), Stokkermans, T.C.A. (author), Ragni, D. (author), Eitelberg, G. (author), Veldhuis, L.L.M. (author)Swirl-recovery vanes (SRVs) enhance propulsive efficiency by converting the rotational kinetic energy in a propeller slipstream into additional thrust. This paper discusses the aerodynamic and aeroacoustic impact of the installation of a set of SRVs downstream of a single-rotating propeller. Experiments were carried out in a large low-speed wind...journal article 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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Sinnige, T. (author), de Vries, R. (author), della Corte, B. (author), Avallone, F. (author), Ragni, D. (author), Eitelberg, G. (author), Veldhuis, L.L.M. (author)An experimental analysis was performed of the unsteady aerodynamic loading caused by the impingement of a propeller slipstream on a downstream lifting surface. When installed on an aircraft, this unsteady loading results in vibrations that are transmitted to the fuselage and are perceived inside the cabin as structure-borne noise. A pylon...journal article 2018
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Arce Leon, C.A. (author), Merino Martinez, R. (author), Ragni, D. (author), Avallone, F. (author), Scarano, F. (author), Pröbsting, S. (author), Snellen, M. (author), Simons, D.G. (author), Madsen, Jesper (author)The broadband noise generated by the scattering of turbulent flow at the trailing edge of a NACA 0018 airfoil with trailing edge serrations is investigated, varying both the airfoil angle of attack and serration flap angle. Acoustic emissions from the trailing edge are measured using a microphone array. The noise level is observed to be...journal article 2017