An application of cantilevered plates subjected to extremely large amplitude deformations: A self-starting mechanism for vertical axis wind turbines

Abstract

The use of Darrieus straight-bladed vertical axis wind turbines (VAWTs) are becoming increasingly attractive for wind energy harvesting thanks to their distinctive advantages, even though these lift-force driven wind turbines suffer from anaemic self-starting capability, especially in areas with irregular wind regimes. In this paper, a novel self-starting mechanism is proposed for VAWTs. The proposed concept centres on the use of pliable plates in either of two distinct configurations: (i) with plates attached to the trailing edge of the rigid airfoil-shape blades of the VAWT; (ii) with plates installed inside the VAWT at a distance from the rotor. The feasibility of these designs for self-starting has been investigated theoretically. In particular, flexible blades are idealized as cantilevered beams placed at an angle to a uniform steady flow. Using a Hamiltonian framework, a geometrically-exact fluid-elastic continuum model is developed for the extremely large-amplitude deflections of the flexible blades. The fidelity of the developed framework is first validated against two sets of experimental data available in the literature. The developed framework is then used to estimate the static torque coefficients generated by the flexible plates in both aforementioned VAWT configurations. Finally, the self-starting efficacy of the proposed design is compared against a Savonius based mechanism used in a well-studied benchmark Darrieus–Savonius turbine. The numerical simulations reveal that, regardless of the initial static positions of the turbine, proper engineering of the pliable plates results in a torque generation capability which spins the turbine, even at low wind speeds. This finding proves the feasibility of the proposed concept as a potential self-starting mechanism for VAWTs. The advantages of this mechanism, such as easier design, manufacturing and implementation, enhanced reliability and economical maintenance, make this concept worthwhile for further exploration.