Hydrodynamic characteristics of a ducted tidal turbine in yawed conditions

In marine environments, tidal currents exhibit periodic changes in both direction and velocity. Consequently, tidal turbines often operate under yawed conditions. While conventional horizontal-axis turbines show decreased performance and undergo periodic load fluctuations due to blade rotation when yawed, research on the effects of yaw on ducted turbines has been sparse, leaving the underlying impact mechanisms poorly understood. This paper presents a three-dimensional hydrodynamic model of a ducted turbine, developed using the computational fluid dynamics method and validated through flume experiments. The hydrodynamic characteristics of the ducted turbine when operating under yawed conditions are analyzed using large eddy simulation. The findings indicate that yaw does not alter the optimal rotational speed of the ducted turbine. The turbine performance remains superior to non-yawed conditions up to a yaw angle of approximately 7 degrees, peaking with a 1% improvement at 5 degrees, but deteriorates beyond this point, declining by 1.5% at a yaw angle of 10 degrees. In addition, yaw causes a deflection in the wake of the ducted turbine. This deflection increases with the yaw angle, reaching its maximum at a yaw angle of 10 degrees with an angle of about 3.4 degrees, before diminishing. The duct structure significantly influences this deflection, while rotor rotation has a minimal impact on wake deflection.