Energy performance and flow characteristics of a NACA0009 hydrofoil with bending shrinkage groove and tip winglet

In this work, a bending shrinkage groove and tip winglet approach is used for improving the energy performance and suppressing the tip leakage vortex (TLV) in a NACA0009 hydrofoil to enhance its characteristics for tidal energy conversion. Numerical calculations are performed by using a structured mesh to solve the Navier-Stokes equation to evaluate the effects of a bending shrinkage groove and tip winglet on hydrofoil performance under no-cavitation condition and cavitation condition. The accuracy and reliability of the numerical methods are verified by comparing with experimental results. Results show that primary tip leakage vortex generation is suppressed by the bending shrinkage groove through the impact of groove jet impingement and that the secondary tip leakage vortex is weakened by the groove breaking flow. The flow separation phenomenon at the pressure surface is suppressed, and the pressure gradient in the shape is reduced by changing the wing thickness near the tip clearance to form different bending shrinkage grooves. The results show that the vortex intensity and the volume of the TLV is suppressed by the bending shrinkage groove. For a curved tip winglet, the vortex area was decreased by up to 19.3%. The lift-drag ratio of the hydrofoils was improved by the bending shrinkage groove, with maximum increase of 22%. In addition, the curved tip winglet structure can reduce the generation of vortex and generate smooth streamline. Simulation results indicate that the performance of a NACA0009 hydrofoil is most improved with a curved tip winglet. Compared with the traditional tip clearance research, the research on the six composite tip clearance in this paper can reveal the influence of tip clearance structure on the hydrofoil performance. It lays a solid foundation for the further engineering application, such as the application of composite structure on cavitation and flow noise.