Wind energy is a clean and sustainable power source that has gained significant attention in recent years. Among all renewable energy technologies, wind power stands out as the most mature and rapidly expanding sector. Over the past decade, global wind power capacity has consistently grown at double-digit rates, with offshore wind energy witnessing a particularly sharp increase. As offshore wind farms move into deeper waters, floating wind turbines have become a focal point for both researchers and industry leaders.
Floating wind turbines are subject to complex oscillatory motions caused by the combined effects of wind and waves. These movements significantly impact the turbine’s safe operation and aerodynamic performance. Moreover, the interaction between the floating platform, mooring system, hydrodynamic forces, structural dynamics, and aerodynamic loads presents major challenges in accurately simulating and evaluating these systems.
Since 2002, several researchers—including Bulder, Lee, Wayman, Vijfhuizen, Henderson, Withee, Fulton, and Nielsen—have explored preliminary designs of floating wind turbines. In 2006, Jonkman and his team at the National Renewable Energy Laboratory (NREL) developed a fully coupled model integrating pneumatic, hydrodynamic, control, and structural elements, and designed three different floating platforms.
To better understand the dynamic and aerodynamic behaviors of floating wind turbines, the blade research team at the Institute of Engineering Thermophysics, Chinese Academy of Sciences, conducted extensive simulations under various wind and wave conditions. They analyzed the motion patterns and angle-of-attack variations of different floating turbine models.
Their findings revealed that swaying motion is the most dominant type of movement. The average sway is primarily influenced by wind speed, while the amplitude depends largely on wave height. By studying the angle-of-attack variations, the team investigated the two-dimensional dynamic stall characteristics of thick airfoils. They found that while the lift coefficient shows minimal dynamic stall effects, the drag and pitching moment coefficients are highly affected.
The oscillatory motion not only alters the aerodynamic performance of the rotor but also affects the interaction between the turbine and its wake, thereby modifying the wake structure. To study this phenomenon, the team improved the actuating line method commonly used in wake analysis and developed a two-dimensional brake line model. The results showed that the new model offers higher accuracy and reduces computational time by approximately 10%.
Based on the dynamic response characteristics of floating wind turbines, the research group built a swing test bench that simulates the oscillatory motion within a wind tunnel. They conducted a series of steady and unsteady experiments on model wind turbines, analyzing power output and load fluctuations under different conditions.
This research was supported by the National Natural Science Foundation of China under the project “Study on the Three Dimensional Flow and Dynamic Stall Characteristics of Floating Wind Turbines†(No. 50976117). The findings were published in the *Journal of Engineering Thermophysics* (2013, 34(7): 1256–1261).
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