Dynamic loading characterization of a horizontal axis tidal current turbine

Abstract

In the present work, a parameter study across a range of intrinsic wave periods, wave heights, current velocities, hub immersion depths, yaw misalignments and tip speed ratios on the dynamic behavior of blade root bending moments has been performed. For evaluating the dynamic loading, a modified unsteady Blade Element Momentum (BEM) model was prepared and coupled with linear and non-linear wave theories. Firstly, a validation study with previous experimental and numerical work was performed. Fifth-order model gave more realistic results taking in consideration the effects of current on wave properties. So, the parameter study calculations were performed using the fifth-order model. The effect of varying wave period, wave height and current velocity with and without the presence of yaw misalignment range on the response of root bending moments has been studied. In addition, the effects of tidal immersion depth variation at different flow conditions have been investigated. Also, the bending moments’ behavior due to the change of tip speed ratio has been studied.Through investigating the effects of wave height, wave period and current velocity variation in the presence of yaw misalignment range, it has been observed that the in-plane bending moments reduction over their median loading have a greater reduction at high wave heights and steep waves respectively. Furthermore, yaw misalignment variation became more influential at higher velocities, while the in-plane bending moments reduction to average loadings had greater values at low velocities. Due to wave height and wave period increase, the maximum loading ranges of 233% (more than the double) of the median out-of-plane bending moment and 146% of the median in-plane bending moment were observed. The submergence ratio reduction seemed to have minor effects even with increasing the current velocity, while had a higher influence at increased wave heights. Also, the excessive increase in the turbine rotational speed has caused a significant increase in the in-plane bending moment frequency oscillations, which in turn affects the quality of the electricity production.