Wind energy stands out as one of the most promising renewable energy sources, with wind power generation being its primary application. As offshore and low-wind-speed regions become more viable for wind farms, multi-megawatt horizontal-axis wind turbines have become the standard. The performance of these turbines heavily depends on their blades, making the development of high-performance airfoils a critical factor in improving energy capture efficiency.
Since the 1980s, researchers have focused on creating specialized airfoil families tailored for wind turbine blades, moving away from traditional aviation-based designs. However, early airfoils were often too thin for the blade’s root region, limiting their effectiveness. With the increasing size of modern wind turbines and the need to operate in harsher environments, there has been a growing demand for thicker, more robust airfoils that can handle higher loads and maintain stability under complex flow conditions.
One effective approach is the use of blunt trailing edge designs, which enhance both aerodynamic performance and structural strength. Researchers like Timmer, Hoerner, and van Dam have explored this concept extensively, including modeling thick trailing edges and studying how bluntness affects performance. Despite these efforts, current design standards still fall short of meeting the needs of multi-megawatt turbines, especially in terms of large-thickness, blunt-edge airfoils.
In response, the Institute of Engineering Thermophysics at the Chinese Academy of Sciences began developing wind-specific airfoil families suitable for China's unique wind conditions in 2007. These include four large-thickness airfoils with relative thicknesses ranging from 45% to 60%. However, earlier designs had limited trailing edge thickness, and XFOIL could not accurately predict performance at high angles of attack. Recent advancements have led to the creation of four new large-thickness, blunt-trailing-edge airfoils tailored for 5-megawatt turbines.
Studies show that airfoils with 45% to 60% thickness are primarily used in the inner part of the blade (10%–20% span). Due to blade twist, the angle of attack in this region is significantly higher, often exceeding the stall angle. This means that traditional lift coefficient metrics are no longer sufficient. Instead, the focus has shifted to ensuring smooth lift coefficient variation and stability across different Reynolds numbers, which is crucial for maintaining consistent turbine output.
Aerodynamically, the design criteria for these thick airfoils emphasize lift coefficient stability rather than peak values. At high angles of attack (15°–25°), the lift coefficient increases steadily, reaching up to 1.7. This behavior, combined with good Reynolds number independence, makes them ideal for efficient and stable wind turbine operation.
To validate these designs, experiments were conducted at the D-4 wind tunnel at Beijing University of Aeronautics and Astronautics, showing that the RFOIL airfoil provides accurate lift predictions up to 25°. Using a hybrid design method, the RFOIL family ensures geometric consistency while delaying boundary layer separation to maintain high lift levels.
Compared to the widely used DUV W2-401 airfoil from Delft University, the new 45% thickness RFOIL demonstrates superior performance. It is now being tested in wind tunnel experiments and is being considered for future multi-megawatt turbine blade designs.
This research has been supported by the National “863†Plan Project titled “Big Thickness, Blunt Trailing Edge, Low Noise Airfoil Design and Application Technology†(No. 2012AA051303). Findings will be presented at the 2013 Academic Conference of the Chinese Society of Engineering Thermophysics in Hohhot and published in the Journal of Engineering Thermophysics.
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