5.2.1.3 Vertical axis rotors

These designs (fig 5.5) may be less familiar, and rather surprising. They also make use of aerodynamic 'lift' effects, but rely on the relatively small component acting forwards along the chord of the aerofoil (the wing shape is effectively 'sucked' forwards as long as the relative wind is slightly inclined to it, rather like a boat sailing very close to the wind). Their conceptual advantages are that they will accept wind from any direction and the blades are designed to withstand high speeds of rotation. In the case of the Darrieus design, the blade takes a 'Troposkien' shape rather like a skipping rope, such that the only forces are tensile along the blade. The variable geometry design uses straight blades which automatically furl themselves at high speed (as on the right hand side of fig 5.5). These rotors may be heavier than propeller types, but do not require elevated machinery and may not even need a support tower at all (Darrieus rotors only need cables to support the upper bearing).

 

Darrieus (Troposkien shape)		Variable geometry

Figure 5.5 Some lift type vertical axis rotors