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.
Highlights
Wind turbines are increasingly installed in the northeastern and the mid-Atlantic US, Canada, and Northern Europe due to good wind resources and land availability
Germanischer Lloyd (GL) ice mass distribution is defined by modeling this nature of ice accumulation, so this guideline is more applicable in the absence of by modeling this nature of ice accumulation, so this guideline is more applicable in the absence of global design guidelines for calculating wind turbine loads in cold climate
Out of the two ice shapes analyzed in this study, Ice shape 1 causes a greater drop in the power output compared to Ice shape 2 for the same amounts of ice mass
Summary
Wind turbines are increasingly installed in the northeastern and the mid-Atlantic US, Canada, and Northern Europe due to good wind resources and land availability. They analyzed the influences of ice mass on natural deflection),and bydynamic considering only the mass changes blade. These two ice are replicated on the Tjaereborg 2 MW wind turbine blade aerofoils to investigate their influence shapes are approximated using discrete Fourier sine series whose coefficients can be scaled to add on the modal behavior of the blade These two ice shapes are approximated using discrete Fourier any desired amount of ice on the leading edge of aerofoil sections. Structural and aerofoil details of sine series whose coefficients can be scaled to add any desired amount of ice on the leading edge this wind turbine blade are reported in [12,13], which is a constant speed pitch controlled turbine. Linear partial differential equations governing the vibration behavior of wind turbine blade are The resulting equations are given in Appendix.
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