Numerical investigation of vertical-axis tidal turbines with sinusoidal pitching blades

In this paper, numerical simulations are conducted to compare the performances of a fixed-blade vertical-axis turbine (VAT), and a variable pitch VAT whose blades are forced to do sinusoidal pitching. The numerical model is based on the Navier-Stokes equations and shear stress transport (SST) k-ω turbulence model. At first, the output characteristics of fixed-blade turbines and variable pitch turbines with different amplitude of pitching, including power coefficient, torque coefficient and ripple factors, are compared. Then the hydrodynamic torques, tangential and normal forces on a blade are compared as well. The comparison reveals that sinusoidal pitching of the blades greatly improves the performance of the turbine. With an appropriate amplitude of pitching, not only the power efficiency increases, but the fluctuation in power output, rotation speed and torque output are suppressed as well. Results also show that the hydrodynamics forces on a blade of a variable pitch turbine are lower than those of the fixed-blade turbine.