Why are the wind turbines today three bladed?

Answer 1

The number of blades involves design considerations of:-

• aerodynamic efficiency
• component costs
• system reliability
• and finally aesthetics

Over the last 50 years wind turbines have almost universally used either two or three blades because while aerodynamic efficiency increases with number of blades, it does so with diminishing returns.

Thus increasing the number of blades from one to two yields a six percent increase in aerodynamic efficiency, and increasing the blade count from two to three yields only an additional three percent in efficiency.

This means that increasing above three yields minimal only improvements and put up the component costs of the turbine (the fewer the number of blades, the lower the material and manufacturing costs will be).

In addition, the fewer the number of blades, the higher the rotational speed can be because blade stiffness requirements to avoid the blades bending to hit the tower limit how thin the blades can be. Higher rotational speeds reduce peak torques in the drive train, resulting in lower gearbox and generator costs.

Also three blades give system reliability because cyclic loads, when combined together at the drive train shaft, are symmetrically balanced for three blades, yielding smoother operation during turbine yaw.

Finally, aesthetics can be considered a factor, most people find that the three-bladed rotor is more pleasing to look at than a one- or two-bladed rotor.