Speed control and hydrodynamic performance analysis of vertical axis tidal turbine under surge motion

Abstract

In the actual operation of a floating vertical axis tidal turbine (VATT), the VATT undergoes wave-induced motion with the floating carrier, resulting in a constantly changing relative inflow velocity of the VATT. With the VATT rotating at a fixed speed, the tip speed ratio would vary over time, leading to a lower average energy utilization rate. Therefore, a variable speed control model based on surge velocity is proposed, and a CFD numerical method is presented for a VATT rotating at variable speed under surge motion. The proposed variable speed control model is effective in improving the average energy utilization rate, e.g., by 36.09 % at a surge period of 2.9 s and a surge amplitude of 0.1 m, as compared to fixed speed rotation. Based on this, a rapid forecast method for hydrodynamic loads of the VATT during variable speed rotation and surge motion is established, considering the variation of the damping coefficient during fixed speed rotation and surge motion. Compared with the CFD results, the proposed method can quickly and effectively forecast the VATT's hydrodynamic loads. The findings can provide a reference for the speed control of floating VATT in actual operation and the rapid prediction of the VATT's hydrodynamic load.