ABSTRACT
Although wind turbines are called extended gas turbines, they operate at considerably lower speeds and have considerably different operating principles when compared with gas turbines. This chapter discusses horizontal and vertical axis wind turbines. Three-bladed horizontal axis turbines, along with vertical axis turbines such as the Darrieus and Savonius rotors, are briefly discussed. Using actuator disc theory, the flow in propellers is analyzed, and it is shown that the maximum power that can be converted by the rotor is given by the so-called Betz limit of 59% of the available wind energy. Expressions for axial thrust and axial thrust coefficient are derived from actuator theory. For vertical axis turbines, the maximum power coefficient is shown to be 0.33.
