Validation of an actuator line CFD model for tidal rotors in waves

This paper presents an analysis of two tidal rotors in close side-by-side proximity under homogeneous currents and surface waves. Multiphase Large Eddy Simulations with a Volume of Fluid free surface model, and an Actuator Line representation of the rotor are used to simulate their behaviour. The rotor was simulated in proximity to the free surface and to a vertical symmetry plane, mimicking twin-rotor towing tank experiments. Numerical and experimental results are compared, showing that the model accurately predicts loads and power at integrated and blade levels for a range of wave frequencies. Both model and experiments show that waves have a modest effect on mean thrust and power, but induce significant fluctuations. The predicted load fluctuations show a good agreement with experiments although with minor frequency-dependent amplitude underestimations and phase differences which suggest inertial effects not captured by the numerical model. The numerical results also show that waves affect wake development downstream, increasing mixing and driving the formation of large vortex structures dependent on wave frequency. Rotor induction, however, is observed to have a modest influence on the propagation of wave kinematics outside the wake region.