The aerodynamics of high solidity unsymmetrical and symmetrical blade H-Darrieus rotors in low wind speed conditions

Abstract

In this paper, blade-fluid interactions of high-solidity unsymmetrical and symmetrical blade H-Darrieus rotors have been studied using detailed computational fluid dynamics simulations to obtain insight into their performance in low wind speed conditions. In the existing literature, such comparative studies of high-solidity rotors are few, but are required for improving their steady-state performance at low wind speeds. For this study, a thick S815 unsymmetrical airfoil and a NACA0018 symmetrical airfoil have been selected. The effects of variations of low wind speeds have been quantified with respect to their impact on the blade-fluid interactions of the rotors at various azimuthal positions. It has been found that in the advancing stroke, a trailing-edge vortex on the suction side of the S815 blade H-Darrieus rotor as well as the leading-edge shape of the S815 blade are responsible for the higher performance of the unsymmetrical blade rotor. Moreover, in the returning stroke, a strong recirculating secondary vortex interacts on the pressure side of the S815 blade H-Darrieus rotor, which also augments the performance of the unsymmetrical blade rotor. For the symmetrical blade rotor, there are no such blade-fluid interactions with the advancing and returning blades.