The effects of vortex generators on the characteristics of the tip hydrofoil and the horizontal axis tidal turbine blade

Abstract

The blade of horizontal axial tidal turbine (HATT) will experience unsteady characteristics, such as dynamic stall, hysteresis loop, and stall delay, leading to unsteady loads that challenge its performance and survivability in the complex ocean environment with turbulent flow, waves, and shear flow. Installing vortex generators (VGs) on the blade surface effectively controls flow separation and improves the performance of the HATT blades. However, most existing VGs studies focus on two-dimensional models that do not consider the tip vortex, requiring further research to investigate the influence of VGs on the blade tip and their potential benefits. This study investigates the static and dynamic effects of different VGs parameters on the NACA63820 hydrofoil installed at the tip through hydrofoil water tunnel experiments and numerical simulations to understand the advantages of using VGs in this configuration. The results show that VGs alter the pressure distribution on the hydrofoil's surface, leading to the formation of pressure humps in the pressure curve of the hydrofoil section. The number and orientation of these humps depend on the openings of the VGs. This study comprehensively analyzes the factors causing these humps and their effects. In conclusion, installing appropriate VGs at the tip significantly improve the hydrofoil's performance and reduce the size of the hysteresis loop opening. Comparing different VGs identifies optimal parameters for HATT blades and evaluate their performance through numerical simulations. The results show that installing VGs at the 30% chord position of the airfoil section can improves the power coefficient by 1.6% at the optimal blade tip speed and broadens the operating range of the HATT.