Most of you seen a wind turbine while travelling or while roaming at places. You see that 3 blades are there in wind turbine. Did you ever think why only 3 blades, and why not 4 or something else?
Welcome to Engineering Master. In this article, we will explain the reason…
Wind turbine is not a latest invention. People are using the power of wind from thousand of years. Early machines are used to crush grains and pump water. Initially, wind turbines are of many shape and design but later research gives a 3 blade design.
Wind turbine works with the help of wind. Air in motion is called as wind. It is created by temperature difference in earth surface. Warm air rises, then cool air takes its place. This process of movement of air is called convection. Moving air contains kinetic energy. This kinetic energy is used by wind turbines to convert it into electrical energy.
Once the blades are rotating, they create their own headwinds (like what we feel on our face when cycling). The velocity of this additional wind helps to lower the pressure on the back side of the blade and contributes to even more lift. This causes the blade to rotate faster and produce additional headwind. The net effect is that the blades of a turbine spin more rapidly until they reach their maximum velocity.
But Why 3 blades?
If there are more blades on a wind turbine, then torque(force that creates rotation) will be higher and it slows the rotational speed (because of increased drag caused by wind flow resistance). But as we know that, turbine used for generating electricity need to be operated at higher speed and they don’t need much torque. So, for producing power, a very few number of blades is enough.
Since a wind turbine is always faced towards wind, so the blades have to change their direction vertically when there is shift in wind direction. In the case of 2 bladed system, when blades are vertical (parallel to the tower), there is very little resistance to twisting. And when the 2 blades are in horizontal position, the blades span at greater distance from the axis of rotation and experience maximum resistance in twisting. As a result, the twisting motion starts and stops twice per revolution and it leads to stress in turbine.
On the other hand, a 3 bladed turbine has very little vibration. This is because when 1 blade is in horizontal position, its resistance to twisting force is counter balanced by 2 other blades.
This is the reason for using 3 blades are used in wind turbine.