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 rotors (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 read more inclined blades (V-rotors) for maximum power capture.This paper presents a systematic study into the effect of blade inclination angle and chord distribution on VAWT performance for different aspect ratios using a 3D implementation of the 2D actuator cylinder model which has been previously validated against higher-fidelity methods.A systematic approach based on a grid search is used to allow the wider design space to be studied and trends identified.In the case of fixed-chord-length blades, it is found that significant power gains are available through blade inclination, between 12 % and 71 % depending 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 is H-rotors.Optimal chord distributions, which maximise the rotor power coefficient, are then obtained, and a natural blade taper is observed.For rotors with optimal chord distributions, similar power gains are observed through blade inclination, again between 12 % and 71 % depending on blade length.However, rotor configurations with the largest power gains are found to have significantly increased blade mass.
For a given power rating, whilst satisfying limitations on maximum blade root bending stress, it is found that blade volume, a proxy for the blade mass, can be reduced between 16 % and 42 % dependent on blade length, and rotor torque can be reduced between 4 % 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 socksmith santa cruz tip-speed ratio, demonstrating their applicability to turbines using secondary rotors, such as the X-rotor, where high tip-speed ratios are required for efficient power conversion between primary and secondary rotors.