Available Technology

Airfoils for Enhanced Wind Turbine and Cooling Tower Efficiency

Wind power and capacity has risen dramatically with a 2015 increase in global capacity of 23.2%, according to Navigant’s 2016World Wind Energy Market Update. This growth in wind capacity has occurred due to the increase in both on- and off-shore wind turbines and through the increasing presence of grid-connected wind power. As a result of this increased capacity, wind efficiency and blade design is increasingly important. An important parameter for the design of wind turbine, or cooling tower fan, blades involves the design of airfoils especially suited to these applications. These airfoils significantly impact the total performance of the blade and require a maximum thickness, Reynolds number, and lift coefficient to mitigate the effects of drag that reduce power output. Another parameter for the optimal blade design is sensitivity to roughness. A blade with a high sensitivity to roughness, especially Horizontal Axis Wind Turbine (HAWT) blades, suffers greater aerodynamic performance degradation due to naturally occurring accumulations of dirt, bugs, and other airborne contaminants. Furthermore, the removal of these contaminants from HAWTs is time-consuming, difficult, and expensive. In addition, a turbine’s associated noise is also of concern for the wind power industry. Airfoil induced noise, while caused by effects such as inflow turbulence interaction, airfoil thickness, laminar separation bubbles, and boundary layer interaction, hinders the commercialization of both large and small wind turbines and can be mitigated through airfoil designs specifically targeted for wind turbine and cooling tower fan applications.
Abstract: 
Scientists at the National Renewable Energy Laboratory (NREL) have developed a number of airfoil designs to reduce noise, drag, and to optimize the lift coefficient and Reynolds numbers of airfoils: Cooling Tower Fan Airfoils: Scientists at NREL have developed novel airfoils for the blades of a cooling-tower fan ranging in length from three to ten meters that are designed for both the root and the tip region. The family of airfoils for the blade’s root region has a Reynolds number of 500,000, a 14% thickness, and a maximum lift coefficient of 1.5. The tip region airfoil possesses a Reynolds number of 1,000,000, a thickness of 10%, and a maximum lift coefficient of 1.5. These airfoils are largely insensitive to roughness, promote lower solidity bases with lower cascade losses, are lighter weight, and are more cost efficient. Quiet Airfoils for Small and Large Wind Turbines: This novel invention developed by NREL scientists is designed for desirable aerodynamic performance and minimal airfoil induced noise for small and large wind turbines. This design involves two airfoil families suitable for horizontal axis wind turbines (HAWTs) and a variety of other wind turbine designs. Each airfoil family provides a high maximum lift coefficient, exhibits docile stall, remains insensitive to roughness, and achieves a low profile drag. The first family of airfoils maintains maximum lift coefficients of approximately 1.0, 1.1, and 1.2 and Reynolds numbers around 400,000, 400,000, and 250,000 respectively. The second family of airfoils is designed for use with large wind turbines and blades of 15 to 30 meters in length and has three separate airfoils. The first has a thickness of 21%, a maximum lift coefficient of 1.6, and a Reynolds number of 4,000,000, the second has a thickness of 18% with a maximum lift coefficient of 1.5 and a Reynolds number of 3,500,000, and the third maintains a thickness of 15%, a maximum lift coefficient of 1.4, and a Reynolds number of 2,500,000.
Benefits: 
Reduced sensitivity to roughness -Enhanced performance and efficiency -Greater cost efficiency -Reduced operating noise
applications: 
Internal Laboratory Ref #: 
ROIs 99-17, and 01-40
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