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Energies 2016, 9(11), 862; doi:10.3390/en9110862

Influence of Icing on the Modal Behavior of Wind Turbine Blades

Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå 97187, Sweden
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Academic Editor: Rupp Carriveau
Received: 14 June 2016 / Revised: 14 September 2016 / Accepted: 14 October 2016 / Published: 26 October 2016
(This article belongs to the Special Issue Modeling and Simulation for Wind Turbine Loads Analysis)
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Abstract

Wind turbines installed in cold climate sites accumulate ice on their structures. Icing of the rotor blades reduces turbine power output and increases loads, vibrations, noise, and safety risks due to the potential ice throw. Ice accumulation increases the mass distribution of the blade, while changes in the aerofoil shapes affect its aerodynamic behavior. Thus, the structural and aerodynamic changes due to icing affect the modal behavior of wind turbine blades. In this study, aeroelastic equations of the wind turbine blade vibrations are derived to analyze modal behavior of the Tjaereborg 2 MW wind turbine blade with ice. Structural vibrations of the blade are coupled with a Beddoes-Leishman unsteady attached flow aerodynamics model and the resulting aeroelastic equations are analyzed using the finite element method (FEM). A linearly increasing ice mass distribution is considered from the blade root to half-length and thereafter constant ice mass distribution to the blade tip, as defined by Germanischer Lloyd (GL) for the certification of wind turbines. Both structural and aerodynamic properties of the iced blades are evaluated and used to determine their influence on aeroelastic natural frequencies and damping factors. Blade natural frequencies reduce with ice mass and the amount of reduction in frequencies depends on how the ice mass is distributed along the blade length; but the reduction in damping factors depends on the ice shape. The variations in the natural frequencies of the iced blades with wind velocities are negligible; however, the damping factors change with wind velocity and become negative at some wind velocities. This study shows that the aerodynamic changes in the iced blade can cause violent vibrations within the operating wind velocity range of this turbine. View Full-Text
Keywords: wind turbine blade; icing; natural frequency; damping wind turbine blade; icing; natural frequency; damping
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Gantasala, S.; Luneno, J.-C.; Aidanpää, J.-O. Influence of Icing on the Modal Behavior of Wind Turbine Blades. Energies 2016, 9, 862.

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