Effects of solidity on startup performance and flow characteristics of a vertical-axis hydrokinetic rotor with three helical blades

Abstract

The present study aims to explain the characteristics of a vertical-axis lift-type hydrokinetic rotor in its startup stage. The rotor is equipped with three helical blades. The effect of the solidity on performance of the rotor is investigated. The computational fluid dynamics (CFD) and the six degree of freedom (SDOF) methods are employed in combination to solve instantaneous flows and to quantify performance of the rotor. The load coefficient is introduced to mimic the external load. The results show that the torque coefficient varies smoothly with the azimuthal angle, and the minimum exceeds 0.08. With increasing load coefficient, fluctuations of the angular velocity in the startup stage are suppressed, and overall magnitude decreases. This tendency is prominent at chord lengths of 0.14 m and 0.16 m. The optimum tip speed ratio varies inversely with the solidity. The maximum power coefficient increases continuously with the chord length and attains 0.315 at a chord length of 0.22 m. As the chord length increases, low velocity tends to be dominant in the zone enclosed by the blades, and the wake of the rotor expands in vertical direction. © 2023 Elsevier Ltd