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Airfoils for Enhanced Wind Turbine and Cooling Tower Efficiency

National Renewable Energy Laboratory

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Technology Marketing Summary

Wind power and capacity has risen dramatically with a 2015 increase in global capacity of 23.2%, according to Navigant’s 2016 World 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.

Description

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:

Airfoils for wind turbine:

NREL scientists have invented novel airfoils for the tip and mid-span regions of wind turbine blades ranging in length from 10 to 15 meters and 15 to 25 meters. These efficient airfoils are designed to provide maximum lift coefficients and to minimize roughness sensitivity effects. The first airfoil family for the blades ranging in length from 10 to 15 meters is for both the mid-span region and the tip region of the blade, where the mid-span region airfoil involves a Reynolds number between 1,500,000 to 2,000,000, a maximum lift coefficient of 1.4 to 1.5, and a thickness of 17%. The tip region has two airfoil designs, one with a Reynolds number between 1,500,000 to 2,000,000, a maximum lift coefficient of 1.4 to 1.5, and a thickness of 14% and the second with a Reynolds number of approximately 2,000,000, a maximum lift coefficient of 0.7, and a thickness of 16%. The second family of airfoils, those for the blades ranging in length between 15 to 25 meters, also includes separate designs for the mid-span region and the tip region, where the mid-span region airfoils have a Reynolds number of approximately 4,000,000, a maximum lift coefficient of 1.0, and a thickness of approximately 21%. The tip region airfoils must have a Reynolds number of approximately 3,000,000, a maximum lift coefficient of 0.9, and a thickness of approximately 16%. These airfoils are relatively insensitive to roughness and can be made of fiberglass, wood, composite material, and other materials that can withstand environmental forces.

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 and Industries
  • Wind Turbines
  • Cooling Tower Fans
More Information

For more information on NREL's publications on airfoils, please see NREL's Publications Database.

Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Date
Patent 8,197,218
Patent
8,197,218
Quiet airfoils for small and large wind turbines
Thick airfoil families with desirable aerodynamic performance with minimal airfoil induced noise. The airfoil families are suitable for a variety of wind turbine designs and are particularly well-suited for use with horizontal axis wind turbines (HAWTs) with constant or variable speed using pitch and/or stall control. In exemplary embodiments, a first family of three thick airfoils is provided for use with small wind turbines and second family of three thick airfoils is provided for use with very large machines, e.g., an airfoil defined for each of three blade radial stations or blade portions defined along the length of a blade. Each of the families is designed to provide a high maximum lift coefficient or high lift, to exhibit docile stalls, to be relatively insensitive to roughness, and to achieve a low profile drag.
National Renewable Energy Laboratory 06/12/2012
Issued
Patent 6,899,524
Patent
6,899,524
Cooling-tower fan airfoils
A family of airfoils for a blade of a cooling-tower fan, is provided wherein the blade has a root region and a tip region, the family of airfoils comprises an airfoil (30) in the root region of the blade having a Reynolds number of 500,000, and an airfoil (20) in the tip region of the blade having a Reynolds number of 1,000,000, and wherein each airfoil is characterized by a maximum lift coefficient that is largely insensitive to roughness effects.
05/31/2005
Issued
Patent 6,068,446
Patent
6,068,446
Airfoils for wind turbine
Airfoils for the tip and mid-span regions of a wind turbine blade have upper surface and lower surface shapes and contours between a leading edge and a trailing edge that minimize roughness effects of the airfoil and provide maximum lift coefficients that are largely insensitive to roughness effects. The airfoil in one embodiment is shaped and contoured to have a thickness in a range of about fourteen to seventeen percent, a Reynolds number in a range of about 1,500,000 to 2,000,000, and a maximum lift coefficient in a range of about 1.4 to 1.5. In another embodiment, the airfoil is shaped and contoured to have a thickness in a range of about fourteen percent to sixteen percent, a Reynolds number in a range of about 1,500,000 to 3,000,000, and a maximum lift coefficient in a range of about 0.7 to 1.5. Another embodiment of the airfoil is shaped and contoured to have a Reynolds in a range of about 1,500,000 to 4,000,000, and a maximum lift coefficient in a range of about 1.0 to 1.5.
National Renewable Energy Laboratory 05/30/2000
Issued
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
ROIs 95-13, 99-17, and 01-40DevelopmentAvailable11/04/201611/04/2016

Contact NREL About This Technology

To: Erin Beaumont<erin.beaumont@nrel.gov>