Copyright © A. Filippone (1999-2003). All Rights Reserved.

World of Aerodynamics

Wind Energy Systems


Old wind mill New wind mill
Figure 1: Old and New wind mills (compare sizes)

Fig. 1 above shows the old and the new way of building windmills (or wind turbines). The Old mill is a very common sight in the Baltic island of Oland (Sweden); the new wind turbine is the giant 2 MW Tjaereborg turbine (Denmark).

In recent years, development of the new variable-pitch wind turbines, along with sophisticated electronic controls, has produced machines that can operate at their rated power output over a wide range of wind speeds.

How it Works

The idea to capture the energy from the wind is very old, and the wind mill shown above is a prove that a grasp of elementary aerodynamics was a basic knowledge of farmers several centuries ago.

The wind can be captured by proper design of the blades. Rotation can be maintained for as long as there is an axial momentum on the shaft that is balanced by some resistance (namely an electric generator). The simplest model consists of a streamtube of air flowing through the rotor disk that looses speed and increases pressure in the process.

More Physics

The ability to control three-dimensional unsteady separated flow could dramatically improve both performance and life span of a wind turbine. Hence the interest in sophisticated CFD methods.

Selected References

  • Spera AD. (editor), Wind Turbine Technology, ASME Press, 1994.

  • Hansen MOL. Aerodynamics of Wind Turbines, James and James Science Publ. 2000 (ISBN 1-902916-06-9)

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Copyright © A. Filippone (1999-2003). All Rights Reserved.