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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°, peaking with a 1% improvement at 5°, but deteriorates beyond this point, declining by 1.5% at a yaw angle of 10°. 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° with an angle of about 3.4°, before diminishing. The duct structure significantly influences this deflection, while rotor rotation has a minimal impact on wake deflection. [ABSTRACT FROM AUTHOR]

The wake development of a tidal turbine should be fully considered in the array arrangement. There are many studies on wake characteristics, mainly focusing on a conventional horizontal-axis turbine, while a ducted turbine has attracted little attention. This paper investigates the wake characteristic of a ducted turbine using flume experiments and large eddy simulations. An analytical wake model of the ducted turbine is proposed and verified by the wake profile under different inflow velocities and the downstream turbine performance under different tandem arrangements. The results show that a ducted turbine wake still maintains a high self-similarity, and the wake profile is approximately the double-Gaussian curve. Compared with a conventional tidal turbine, a ducted turbine has a faster wake recovery speed, but a larger radial influence range. Therefore, ducted turbine arrays should be configured with wider radial distances and shorter axial distances. [ABSTRACT FROM AUTHOR]

• A CFD model of the tandem arrangement of ducted tidal turbines is established based on LES. • Flume experiment is carried out to verify the CFD model. • Turbine-turbine interaction influenced by tandem distance is studied. • Suggestions on the tandem arrangement of ducted tidal turbines are put forward. Array research of tidal turbine is critical to make it cost-effective and commercializing. There are many studies of turbine arrays, which mostly focus on a conventional horizontal-axis turbine. While a ducted turbine is also available for commercial application, which draws little attention. In this paper, the tandem arrangement of ducted horizontal-axis turbines is studied based on the flume experiment and the large eddy simulation (LES). The turbine's performance changes are investigated under the 5-15D (D represents the turbine diameter) tandem distance. Research results show that the downstream turbine's performance degrades significantly, and its efficiency drops to roughly half of the upstream turbine when the tandem distance is 5-10D. When the distance increases more than 10 D , the downstream turbine performance can reach 80% of the upstream turbine. As the distance increases, this performance recovery becomes less significant. In terms of load fluctuation, with the interaction of the upstream wake and the surrounding flow field, a spiral oscillation wake region will be formed about 10 D behind the upstream turbine. Therefore, with the increase of the tandem distance, the load fluctuation of the downstream turbine does not gradually decrease as a result. This fluctuation is more than twice that of the upstream turbine, and the maximum can reach 5 times. [ABSTRACT FROM AUTHOR]

A counter-rotating tidal turbine can balance the axial torque and accelerate the wake recovery, leading to a more conducive array layout. This paper aims to investigate the coaxial-rotor interaction, considering variable rotor distance and rotation speed. A numerical model based on large eddy simulation (LES) is established to study the hydrodynamic performance of this turbine, and it is validated by a flume experiment. The research results show that the upstream rotor performance is severely degraded when the two rotors are configured with narrow distance; while this distance is too wide, the downstream rotor bears a large fluctuating load induced by the fully developed wake. In terms of rotation speed, the efficiency of the upstream rotor decreases with the acceleration of the downstream rotor, but the maximum reduction is less than 10%. Moreover, a severe disturbance region will be generated behind the upstream rotor caused by blade root vortex shedding, and the downstream rotor should be positioned far away from this region. Overall, the current two-rotor system can achieve the best energy efficiency at the rotor distance of 0.4D. Compared with a single rotor, this system improves power efficiency by nearly 10%. • A CFD model of a two-rotor turbine is established based on LES. • Flume experiment is carried out to verify the CFD model. • Two-rotor interaction influenced by two-rotor spacing and rotor rotation speed is studied. • Suggestions on the configuration of the two-rotor turbine are given. [ABSTRACT FROM AUTHOR]