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Effects of helical-shaped blades on the flow characteristics and power production of finite-length wind farms composed of vertical-axis wind turbines (VAWTs) are studied numerically using large-eddy simulation (LES). Two helical-bladed VAWTs (with opposite blade twist angles) are studied against one straight-bladed VAWT in different array configurations with coarse, intermediate, and tight spacings. Statistical analysis of the LES data shows that the helical-bladed VAWTs can improve the mean power production in the fully developed region of the array by about 4.94 % – 7.33 % compared with the corresponding straight-bladed VAWT cases. The helical-bladed VAWTs also cover the azimuth angle more smoothly during the rotation, resulting in about 47.6 % – 60.1 % reduction in the temporal fluctuation of the VAWT power output. Using the helical-bladed VAWTs also reduces the fatigue load on the structure by significantly reducing the spanwise bending moment (relative to the bottom base), which may improve the longevity of the VAWT system to reduce the long-term maintenance cost. [ABSTRACT FROM AUTHOR]

Wind turbines' participation in frequency response is known to improve the frequency stability of power systems, but it can also have a negative impact on the fatigue load of wind turbines. The objective of this paper is to investigate the effect of frequency response on the fatigue loads experienced by various components of a wind turbine, including the low-speed shaft, tower, and blade. To achieve this goal, the authors develop a model of a variable speed horizontal-axis wind turbine based on a doubly fed induction generator. They derive explicit analytical equations of low-speed shaft torque, tower bending moment, and blade bending moment to describe the fluctuations of torque and moment related to the operating states of wind turbines, such as generator torque, rotor speed, and pitch angle, under frequency response. These equations allow for the evaluation of the impact of frequency response on torque and moment changes and fatigue load. Spectral density analysis and modal analysis are used to further analyze the analytical equations, examining the influence of frequency response on different operating conditions of wind turbines and determining the mechanism by which frequency response affects fatigue load qualitatively and quantitatively. The authors use the FAST V8 Code based on the NREL offshore 5-MW baseline wind turbine to demonstrate the effectiveness of the proposed analysis method in evaluating fatigue loads affected by frequency response. The results show that the fatigue load on the low-speed shaft and the lateral side of the tower will significantly increase due to wind turbine participation in frequency response. [ABSTRACT FROM AUTHOR]

Wind turbines installed in external environments are subject to a combination of various environmental and operational conditions during their lifetimes, resulting in varying mechanical loads on each of their components. These loads directly impact the turbine lifetime; therefore, research aimed at reducing the load on each component of the wind turbine is required. In this study, load analysis was performed by applying various load reduction control systems. The effect of the load reduction was verified for each controller through individual simulations. Finally, the design load cases (DLC1.1–DLC8.1) required to evaluate the ultimate and fatigue loads based on the IEC 61400-1 ed.3 international standard were defined, and the loads with respect to a 4 MW wind turbine with and without various load reduction systems were calculated. When applying all load reduction controllers, the turbine blades and the tower experienced ultimate load reductions of 1%–31% and 7%–21.7%, respectively, except the tower's side-to-side bending moment. This moment was observed in the idling condition, which was not affected by the control system; hence, no changes were observed in the load. Fatigue equivalent load reductions were also observed at the blade (3%–8.9%) and tower side-to-side load (4.8%–7.8%). Notably, however, the tower fore-aft fatigue load increased by 10% in most sections. This overall load reduction suggests that turbine components can be fabricated using less material, thereby increasing the wind turbine fatigue lifetime. This result is expected to reduce the levelized cost of energy. [ABSTRACT FROM AUTHOR]

When wind turbines operate in complex atmospheric environments, the flow fields around their blades are complex and unsteady. To capture the lag characteristics of induced velocity when the dynamic environment of a rotor changes, this study further modified the equilibrium wake model using the blade element momentum and acceleration potential theories. In addition, a novel expression for the added mass force m A = 128 / 75 ρ R 3 was derived. Consequently, a numerical aerodynamics model of a rotor with an added mass force was developed. The model was used to calculate the aerodynamic load of a 5 MW wind turbine under steady wind, turbulence, gust, wind direction change, and rapid pitching. The results demonstrated that the numerical model with added mass force could reflect the rotor aerodynamic performance more accurately than its counterpart. The fluctuation amplitudes of the flapwise and edgewise bending moments of the blade root were smaller than those from the equilibrium wake model. The overshoot in loading, which was caused by the added mass force during pitching, could not be ignored. The research results were compared with experimental data from the National Renewable Energy Laboratory. It was found that the proposed model provided a new strategy for calculating the added mass force and predicted rotor aerodynamic loads more accurately than the model without added mass force. [ABSTRACT FROM AUTHOR]

The increasing size and complexity of wind turbine blade designs challenge the ability of traditional fatigue testing methods to accurately and efficiently reproduce load distributions representative of real world conditions. A new two-stage approach is proposed. In the first stage, the blade is subjected to a dual-axis resonance test, where additional masses are mounted to the blade to control the bending moment distribution. In the second stage, part of the blade is removed, allowing it to be exercised at a higher frequency and for more damage to be applied to the root and transitional sections. The results of the proposed method were compared with those of traditional testing methods for 38 m and 60 m blades. The results indicate that the new methods have the potential to significantly improve accuracy, but the testing duration will increase. [ABSTRACT FROM AUTHOR]