Experimental study on power characteristics of a horizontal-axis tidal turbine under pitch motion

The effect of pitch motion on the power characteristics of a floating horizontal-axis tidal turbine was investigated using model experiments. Based on the water flume's size, a tidal turbine test rig with uniform pitch and simple harmonic motion was designed. The effects of various pitch periods (2.7-4.7 s) and amplitudes (3-9 degrees) on the power characteristics of the tidal turbine under the free surface were analyzed. The excitation of the pitch motion caused the instantaneous value of the tidal turbine power to fluctuate. The degree of power fluctuation was similar for different tip-speed ratios. The fluctuation amplitude increased and decreased approximately linearly with the period and amplitude, respectively. The mean power under pitch motion was slightly higher than that under the fixed state, representing an improvement of approximately 2.75-3.84%. Large-amplitude and highfrequency pitch motions were detrimental to the rotational speed control of tidal turbines and led to severe fluctuations in the power output. The experimental results provide detailed data for designing the motion response of the floating platform, power output control of the tidal turbine, and validation of the numerical model for the multi-degree-of-freedom hydrodynamic analysis of a floating tidal turbine.