ABSTRACT
Vertical axis wind turbines are classified into two families: aerodynamic action turbines (Darrieus type) and reaction turbines (Savonius type). This chapter discusses the aerodynamic action turbines. Darrieus turbines have two big limitations that have hampered their massive diffusion, especially in the market of small installations. The first limitation is that such turbines operate in a narrow interval of λ values, ranging from four to eight, and furthermore they are not capable of starting autonomously. The second limitation is that their CP is intrinsically lower than that of horizontal axis turbines, because of their particular operation principle. A theory of Darrieus turbines based on Glauert's theory of horizontal axis turbines ignores the effect of the trail vortexes of the upstream blades on the downwind ones. The driving forces of the Darrieus turbines can be described in detail by means of the "element of blade theory".
