Page 85 - Fluid Power Engineering

CHAPTER5

Advanced

Aerodynamics of

Wind Turbine Blades

Aeronautics was neither an industry nor a science. It was a miracle.
—Igor Sikorsky

Introduction
In this chapter, advanced topics related to aerodynamics of wind tur-
bines are covered. The previous chapter was an introduction to the
basic concepts of airfoil, lift, and drag. In this chapter, the first section
will describe the blade element theory, which is an enhancement over
the rotor disk theory. In the rest of the chapter, the manifestations of the
aerodynamic theory on the performance of turbines will be discussed.
Specifically, power performance curves of different configurations of
wind turbines are presented. The configurations discussed include
constant versus variable speed rotor and stall versus pitch regulation.
The chapter ends with a brief description of the vertical axis wind
turbine.

Blade Element Model
The blade element model (BEM) is more rigorous compared to the ro-
tor disk model. This model is used to derive theoretical performance
curves of wind turbines. BEM computes the axial force and the torque
(tangential force multiplied with the radius along the blade). The ax-
ial force is then equated to the rate of change of momentum along

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