Performance and near-wake characteristics of a bidirectional horizontal-axis tidal turbine

Horizontal-axis tidal turbines (HATTs) have the potential to produce considerable amount of clean renewable energy from ocean tides. To reduce costs and improve reliability, a full-scale bidirectional HATT (BHATT) with a centrosymmetric hydrofoil was designed to operate in two opposite flow directions. To better understand the performance and the near-wake characteristics of the BHATT, a three-dimensional (3D) numerical model with a k-omega SST model and a sliding mesh method was applied. The numerical framework was validated using two different experiments, and the mesh convergence was tested. The result shows that the BHATT can achieve a power coefficient of 43.5% at design tip speed ratio (TSR), and cause a remarkable circumferential flow in the near-wake from it. In addition, the presence of a support structure causes a decrease and a fluctuation in both power and thrust coefficient, especially when the rotor is downstream from the support structure. Similarly, a misalignment also leads to a decrease in both power and thrust coefficient. However, it causes almost no fluctuation. Finally, the influence of different support structures on the performance of the BHATT in different misalignment cases was studied.