Page 95 - Fluid Power Engineering

Advanced Aerodynamics of W ind T urbine Blades 73

FIGURE 5-7 Vertical
axis wind turbine of R
H-rotor type.
H

changes continuously, which causes the torque to pulsate. The
pulsating torque and high centrifugal force causes structural
failures.
H rotor or Giromill VAWT. This is similar to a Darrieus VAWT,

but the blades are parallel to the axis of rotation. Among small
VAWTs, this has become a popular configuration (see Fig. 5-7).
The blades are in the shape of an airfoil. The angle of attack
changes as the blades rotate around the axis, which causes the
lift and drag to be unfavorable in certain sectors of rotation.

The overall advantages are that the VAWT are:

Simpler because they do not require a yaw or pitch mecha-

nism.
All the components that would traditionally be in a nacelle

are on the ground, making maintenance easier.
Rapid changes in the direction of the velocity vector in the

horizontal plane can cause a horizontal axis turbine to “seek
the wind” by changing the axis of rotation of the blades. This
seeking can cause a significant loss of energy. Vertical axis
turbines do not have this problem.

Despite the advantages, VAWT have not become popular because:

Lower theoretical efficiency and lower practical efficiency.

Lower installed heights leading to lower wind speeds and

lower energy production.