Wind Turbine Blade Aerodynamics: Horizontal Axis Turbines
A rotating turbine blade experiences oncoming wind differently, which is called relative wind. A section of the turbine blade receives a wind velocity differently due to its rotation.
The interaction between oncoming wind and a blade generates lift and drag forces. Drag force is in the same direction as the relative wind, and it holds the blade back. The lift force is perpendicular to the relative wind (Figure 1). A maximum lift and minimum drag forces are needed to achieve a higher power coefficient.
Modern Wind turbine blades have an airfoil shape to get an optimal angle of attack and greater lift force (Figure 2).
An angle of attack above certain degrees increases the drag force and causes a stall (Figure 3).
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| Wind Turbine Blade |
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| Figure 1* |
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| Figure 2* |
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| Figure 3* |
*Source Figure 1,2,3: Piggott, H., & National Centre for Alternative Technology. (2000). Windpower Workshop: Building your own wind turbine. Machynlleth, Powys, United Kingdom: Centre for Alternative Technology.