5 Wind Turbines
Wind turbines are classified according to the interactions of the blades with the wind (aerodynamics), orientation of the rotor axis to the ground, and innovative or unusual types of machines. The aerodynamic interaction of the blades with the wind is caused by either drag or lift, or by a combination of both.
5.1 DRAG DEVICES
In a drag device, the wind pushes against the blades or sails (Figure 5.1). Drag devices are inherently limited in efficiency because the speed of the device or blades cannot exceed the wind speed. The wind pushes on the blades of a drag turbine, forcing the rotor to turn on its axis.
Examples of drag devices are cup anemometers, vanes, and paddles that are shielded from the wind or change parallel ...
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