Effect of Blade Inclination Angle for Straight Bladed Vertical Axis Wind Turbines

Abstract. Vertical Axis Wind Turbines (VAWTs) have received renewed research interest in the offshore environment due to a number of design synergies that have the potential to decrease the cost of energy for offshore wind. Many studies have been completed on the rotor design for straight bladed (H) rotors however there is sparse information on the effect of blade inclination angle on VAWT aerodynamic performance, and the optimal blade design of VAWTs with inclined blades (V-rotors) for maximum power capture.

This paper presents a systematic study into the effect of blade inclination angle, chord distribution, and blade length on VAWT performance. In the case of fixed chord length blades, it is found that significant power gains are available through blade inclination, between 10 % and 68 %, dependent on blade length. This is driven by the increase in rotor swept area. Further investigation indicates that despite this, under maximum blade stress limitations the most economical solution for fixed chord length blades are H-rotors.

Optimal chord distributions to maximise the rotor power coefficient are then obtained, and a natural blade taper is observed. Significant power gains, between 10 % and 69 % dependent on blade length, are observed through blade inclination. However, consideration must be taken to limit blade mass. For a given power rating, whilst satisfying limitations on maximum blade root bending stress, it is found that blade volume can be reduced between 9 % and 42 % dependent on blade length, and rotor torque can be reduced between 3 % and 9 %. This indicates the potential of V-rotors to reduce the cost of energy compared to H-rotors in traditional VAWT designs. Additionally, inclined blades are shown to increase the operational tip speed ratio, demonstrating their applicability to turbines using secondary rotors, such as the X-Rotor.