Wind Turbine Aeroacoustics by Large-eddy Simulation – Acoustic Analogy Approach

Authors

Claudio Bernardi - Department of Mechanics, Mathematics and Management, Polytechnic University of Bari, Bari, Italy
Federico Porcacchia - --
Claudio Testa - CNR-INM, Institute of Marine Engineering, 00128 Rome, Italy
Pietro De Palma* - Department of Mechanics, Mathematics and Management, Polytechnic University of Bari, Bari, Italy
Stefano Leonardi - Department of Mechanical Engineering, University of Texas at Dallas, Richardson, Texas, USA
Stefania Cherubini - Department of Mechanics, Mathematics and Management, Polytechnic University of Bari, Bari, Italy

Abstract

This paper investigates the far-field noise induced by large onshore wind turbinerotors. Acoustic emissions from the horizontal axis three-bladed NREL 5-MW de-vice are predicted by the permeable-surface Ffowcs Williams-Hawkings equations(FWH-P) starting from a Large Eddy Simulation (LES) of the flow past the rotorand nacelle. A computational domain of 20x2.4x2.4 diameter units is considered;the rotor, placed 4 diameters far from the inlet, is modelled by the actuator line ap-proach whereas the nacelle is simulated by the immersed boundary technique. Thetest case is set for a tip speed ratio λ = 7, rotor angular speed ω = 12.1 rpm, andReynolds number Re = 105 [1]. At the design condition, a parametric study of theFWH-P noise signals is carried out by post-processing LES data on different acous-tic surfaces S embedding all the aerodynamic sources of sound. To this aim, thepreliminary analysis of L2 norm of the Lighthill tensor inside the computationaldomain, the placement of eddies downstream the rotor disk, and the satisfaction ofthe acoustic compatibility condition (acoustic pressure equal to zero inside S) drivesize and placement of the porous surfaces [2]. In the attempt of remaining close tothe most resolved CFD zone (where the detection of the hydrodynamic sources ofnoise is expected to be more accurate), alleviating the spurious signals (if any) in-herently associated to the end-cap issues, acoustic results from open/closed acousticsurfaces, in conjunction with those coming from the outflow disk averaging, areproposed. Correlations between acoustic pressures and aerodynamic flowfield fea-tures past/downstream the turbine are presented in order to gain knowledge on themechanisms underlying turbine noise generation and radiation.References. [1] C. Santoni, K. Carrasquillo, I. Arenas-Navarro, and S. Leonardi, “Effect of tower and nacelleon the flow past a wind turbine,” Wind Energy, vol. 20, no. 12, pp. 1927–1939, 2017. [2] C. Testa, F. Porcacchia, S. Zaghi, and M. Gennaretti, “Study of a fwh-based permeable-surface formulation for propeller hydroacoustics,” Ocean Engineering, vol. 240, p. 109828,2021.