Influence of pitching motion on the hydrodynamic performance of a horizontal axis tidal turbine considering the surface wave

A CFD numerical method is established under the wave-current condition, used to analyze the hydrodynamic performance of a horizontal-axis tidal turbine based on floating platform with rotation and pitching motion. The inflow direction load, pitch moment and power coefficients with different depths of the blade tip-immersion, the periods and amplitudes of the pitch, wave heights are obtained. The three coefficients have obvious periodically fluctuated with the pitching and wave frequencies, while the time mean of those have changed little with increasing of the depth of blade tip-immersion, wave height, pitch (wave) period and pitching amplitude. So considering damping and additional mass forces, a load fitting model is established, and the damping and additional mass coefficients are calculated by the least square method. The influence of damping coefficient on the hydrodynamic loads is obvious, while the influence of additional mass coefficient on that can be neglected, and the damping coefficient of inflow direction load coefficient is basically stable. The damping coefficients of the pitching moment and power coefficients fluctuate periodically, but the mean value of damping coefficients keep stable. The research results in this paper are important for studying the coupling motion of the turbine and the floating platform.