Aerodynamics of Wind Turbines
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Before addressing more technical aspects of wind turbine technology, an attempt is made to give a short general introduction to wind energy. This involves a very brief historical part explaining the development of wind ower, as well as a part dealing with economy and wind turbine design. It is by no means the intention to give a full historical review of wind turbines,merely to mention some major milestones in their development and to give examples of the historical exploitation of wind power.
The force of the wind can be very strong, as can be seen after the passage of a hurricane or a typhoon. Historically, people have harnessed this force peacefully, its most important usage probably being the propulsion of ships using sails before the invention of the steam engine and the internal combustion engine.
Wind has also been used in windmills to grind grain or to pump water for irrigation or, as in The Netherlands, to prevent the ocean from flooding low-lying land. At the beginning of the twentieth century electricity came into use and windmills gradually became wind turbines as the rotor was connected to an electric generator.
The first electrical grids consisted of low-voltage DC cables with high losses. Electricity therefore had to be generated close to the site of use. On farms, small wind turbines were ideal for this purpose and in Denmark Poul la Cour, who was among the first to connect a windmill to a generator, gave a course for ‘agricultural electricians’.
An example of La Cour’s great foresight was that he installed in his school one of the first wind tunnels in the world in order to investigate rotor aerodynamics. Gradually, however,diesel engines and steam turbines took over the production of electricity and only during the two world wars, when the supply of fuel was scarce, did wind power flourish again.
