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Understanding the Aerodynamics of Wind Turbine Blades


Introduction

Wind turbines harness the power of the wind to generate electricity. The key element in this conversion is the wind turbine blade, the design and aerodynamics of which play a crucial role in determining the efficiency and performance of a wind turbine. The fundamental science behind wind turbine aerodynamics is rooted in the Bernoulli’s principle and the laws of fluid dynamics, and is closely related to the principles that allow aircraft to fly.



Design

Wind turbine blades are specifically designed to extract the maximum energy from the wind while withstanding a multitude of environmental forces. They typically feature an airfoil shape similar to an airplane wing but with certain modifications. The airfoil shape is typically thicker and wider at the base and tapers towards the tip. This shape is designed to generate lift, reduce drag, and thereby maximize rotational force.


Aerodynamics

The aerodynamics of a wind turbine blade are based on the principles of lift and drag. Lift is the force that pushes the blade away from the direction of the wind, and it is generated by the pressure difference between the sides of the blade. The wind travels faster over the curved, longer side (upper side when oriented vertically) of the airfoil, creating a lower pressure area. Conversely, it moves slower under the shorter, flat side, resulting in a higher pressure area. This pressure difference leads to lift.

Drag, on the other hand, is the force that acts opposite to the direction of the blade's movement. It is caused by the friction of the wind against the blade surface and by the turbulence generated at the trailing edge of the blade.


Efficiency

The ratio of lift to drag, also known as the Lift-to-Drag ratio (L/D), is crucial in determining the efficiency of a wind turbine. Ideally, the blade design should maximize lift while minimizing drag to achieve the most efficient conversion of wind energy into rotational energy.


Pitch and Yaw Controls

To optimize performance under various wind conditions, modern wind turbines use pitch and yaw controls. The pitch of the blade (the angle between the chord line of the blade and the plane of rotation) can be adjusted to optimize the blade's interaction with the wind. During high wind speeds, the blades are pitched to reduce the effective area facing the wind, thereby reducing the risk of damage due to excessive forces.

Similarly, the yaw mechanism adjusts the orientation of the whole turbine rotor towards the incoming wind. Proper yaw control ensures that the rotor faces the wind optimally, making the most efficient use of available wind resources.


How to make sure, the blades are ok?

With the Turbit AI power monitoring all the aforementioned effects on the efficiency of the turbine can be monitored. Even the slightest changes in the power output can be seen and the potential reasons are analyzed automatically. The main reasons we see in an underperformance due to wrong pitch control. Unfortunately most often somebody forgot to reset a pitch limit or a has set up the wrong sound curve. But with Turbit you can also detect general problems like a multiple year long erosion of the leading edge, pitch misalignment, yaw misalignment or other problems.

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