Introduction to Wind Turbine.pdf

Downwind turbines downwind turbines have their blades

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Downwind turbines Downwind turbines have their blades on the lee side (downward) of the tower, as Figure 1b shows. In this way, the wind hits the blades after it hits the tower. The main advantage of downwind turbines is that they do not require a yaw control mechanism. This occurs because these turbines naturally tend to self- orient to the wind direction. The main drawback of downwind turbines is that the tower disrupts the wind flow. This disruption is called tower shadow . Due to the tower shadow, each blade experiences a decrease in air flow once per revolution, as it passes through the lowest point of its circle of rotation. This causes the generated electrical power to decrease momentarily every time a blade passes behind the wind turbine tower. Tower shadow also causes the blades to flex, resulting in turbulence, noise, and blade fatigue. Two bladed wind turbines versus three bladed wind turbines Most contemporary European wind turbines have a three-blade rotor, while American units have tended to have a two-blade rotor. The generated power increases with the number of blades in theory, but in practice, it does not increase significantly beyond three blades. Two-bladed turbines are usually cheaper than three-bladed turbines. They need less structural material than three-bladed turbines, making them lighter and easier to install. They can operate at faster rotation speeds than three-
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Introduction – Wind Turbines Discussion of Fundamentals 4 Introduction to Wind Power bladed turbines before their operation becomes seriously affected by turbulence. However, two-bladed turbines are usually harder to design because they are subjected to high dynamic loads. They can have stability problems because when one blade is at the highest point in the rotation circle, where it receives the maximum wind power, the other blade passes in front or behind the wind turbine tower where some fluctuation in air flow is experienced.
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