The effect of inertia and flap on autorotation applied for hydrokinetic energy harvesting

Abstract

This paper outlines the results for a set of experiments carried out on Vertical Axis Autorotation Current Turbine (VAACT) which is an innovative concept among the other low-head hydrokinetic energy converters. The VAACT is a one degree of freedom hinged plate which utilizes the autorotation phenomenon to rotate about its vertical axis in uniform water current. The state of the art on this turbine is application of the extra moment of inertia and also flapped shape of the rotor blade to improve the autorotation characteristics as the principle of operation of the turbine. Investigation of the effect of the extra moment of inertia and the flap on the operational characteristics such as maximum attainable angular velocity and tip speed ratio, obtainable torque of the turbine and its performance is the main objective of this paper.The VAACT harvests energy efficiently from very low head current. The performance of the flapped configuration of this turbine reaches up to 33% in the very low current velocity. The highest efficiencies occur in the range of 0.65–0.85 of tip speed ratio and also in the range of 0.6–0.7 of the non-dimensional moment of inertia. Furthermore, this study has shown that the flap increases the power coefficient significantly by a factor of up to 5 compared to flat plate type.