Effect of blade chord length on startup performance of H-type tidal current turbine rotor

This study aims to reveal the effect of the blade chord length on the startup performance of the lift rotor that converts the kinetic energy of tidal currents. The computational fluid dynamics technique was used to simulate unsteady flows around the rotor. The six degrees of freedom method was adopted to model the correlation between the rotational speed of the rotor and influential torques acting on the rotor. A comparative analysis of transient flows, rotational speed, and output torque was implemented at different initial azimuthal angles. The results show that as the rotor starts up at the minimum torque, the time required to attain the maximum rotational speed is longer than that associated with the maximum torque. As the maximum rotational speed is reached, low-pressure elements are produced in the area enclosed by the rotor blades, which is insensitive to the initial setting angle. A large area of low pressure is responsible for low output torque. During the startup process, the rotational speed experiences stages of sharp increase, fluctuating decrease, and moderate fluctuation, as is common at different blade chord lengths. As the chord length increases from 0.16 to 0.24 m, the startup process is extended by 0.63 s, and the average rotational speed in the stabilization stage decreases.