Effects of upstream deflector on flow characteristics and startup performance of a drag-type hydrokinetic rotor

Abstract

The present study aims to describe effects of an upstream deflector on flow characteristics and startup performance of a drag-type hydrokinetic rotor. Flow velocity was measured using the time-resolved particle image velocimetry (TR-PIV). The operational performance of the drag-type rotor was measured. The rotational speed of the rotor was calculated using the six degrees of freedom (SDOF) solver. Effects of external loads on the startup performance of the rotor were investigated. The results show that negative torque is eliminated due to the introduction of the deflector. The interaction between the rotating blade and the stationary deflector promotes the growth and collapse of large-scale vortices. The deflector guides the flow towards the advancing blade. The startup process incorporates three distinct stages, namely the acceleration, the rotational speed fluctuation and the rotation stabilization stages. The acceleration stage is extended as the load coefficient increases. During the startup process, the same azimuthal angle corresponds to different flow patterns. As the load coefficient increases, irregular variations of the rotational speed are intensified while the average tip-speed ratio decreases continuously. ? 2021 Elsevier Ltd. All rights reserved.