Vol.:(0123456789) 1 3 CEAS Aeronautical Journal https://doi.org/10.1007/s13272-020-00454-x ORIGINAL PAPER Evaluation of the noise impact of fap‑tip fences installed on laminar wings Lorenzo Burghignoli 1  · Alessandro Di Marco 1  · Francesco Centracchio 1  · Roberto Camussi 1  · Thomas Ahlefeldt 2  · Arne Henning 2  · Stephan Adden 3  · Massimiliano Di Giulio 4 Received: 11 June 2019 / Revised: 5 May 2020 / Accepted: 10 May 2020 © Deutsches Zentrum für Luft- und Raumfahrt e.V. 2020 Abstract The aeroacoustics of laminar wings and the noise abatement provided by fap-tip fences are studied experimentally on a scaled model installed in the closed test section of a subsonic wind tunnel. The activity has been developed under an interna- tional project funded by the European Union through the H2020 Framework Program. The model reproduces an innovative regional aircraft mounting aft-engines and adopting the Natural Laminar Flow concept. Both take-of and landing settings are tested for several combinations of wind tunnel speeds and angles of attack; these confgurations being the most critical from the viewpoint of airframe noise generation. A baseline confguration without fap-tip fences is also tested for a com- parative study. Noise sources are identifed by measuring pressure fuctuations through a phased microphone array. Data are processed using both Conventional Beamforming and CLEAN-SC algorithms to retrieve the sound source maps and the integrated spectra over the areas of interest. Directivity efects are investigated as well by moving the microphone array in diferent axial positions corresponding to diferent aircraft polar directivity angles. The wind tunnel data are eventually extrapolated to full scale and projected to fight condition allowing the analysis of the results in terms of Efective Perceived Noise Level (EPNL). Tests provided an extensive characterization of the acoustic behavior of the analyzed model demon- strating the capability of measurements carried out in a non-anechoic environment, to provide reliable data. The longitudinal traversing of the microphones array allowed us to compute, even though qualitatively, the EPNL and thus demonstrated the feasibility of a procedure that can be a reference for the design of future aeroacoustic tests. The efectiveness of the fap-tip fences to successfully reduce the fap side-edge noise has been defnitely verifed both through the analysis of the acoustic maps retrieved from the beamforming investigation and by the estimation of the overall variation of the EPNL with respect to a baseline reference confguration without low-noise devices. List of symbols A Beamforming output (Pa 2 m 2 ) B Number of grid points C Cross spectral matrix c Speed of sound (m/s) f Frequency (Hz) f s Sampling frequency (Hz) H pr Pressure response curve (dB) L p Sound pressure level (dB) p Pressure (Pa) p ref Reference acoustic pressure (Pa) R Distance between source and observer (m) R  Propagation distance (m) U Wind tunnel nominal speed (m/s) w Weighted steering vector (m) x, y, z Coordinate system of the wind tunnel (m)  Angle of Attack ( ◦ )  polar directivity angle ( ◦ )   Emission angle ( ◦ )  Distance vector (m)  Angular frequency (rad/s) Abbreviations ACARE Advisory Council for Aviation Research and innovation in Europe A/C Aircraft NLF Natural laminar fow * Lorenzo Burghignoli lorenzo.burghignoli@uniroma3.it 1 Department of Engineering, Università degli Studi Roma Tre, 00146 Rome, Italy 2 Institute of Aerodynamics and Flow Technology, German Aerospace Center, Göttingen 37073, Germany 3 IBK Innovation GmBH & Co. KG, 21129 Hamburg, Germany 4 Leonardo Company S.p.A., 80038 Naples, Italy