High-fidelity IDDES simulations of unsteady hydrodynamics and wake evolution characteristics of a tidal current turbine under focused wave-current interaction

Tidal current turbines encounter complex unsteady loads from focused waves and currents in extreme marine environments, significantly impacting their performance. To investigate these effects, a high-fidelity numerical model was developed coupling the linear wave superposition principle (with component wave correction), improved delayed detached eddy simulation, and the volume of fluid method. This model systematically analyzes turbine hydrodynamics and wake evolution under focused wave-current conditions with varying wave amplitudes. Results show that while wave-current interactions have a minor effect on time-averaged coefficients (variations <0.6%), they drastically intensify instantaneous fluctuations. For instance, under extreme conditions, power and thrust coefficient fluctuation ranges increase by approximately 98 and 177 times, respectively, with power output briefly approaching zero at the focusing moment. Frequency analysis reveals that low-frequency power fluctuations are governed by the focused wave peak frequency (∼0.6 Hz), while medium-to-high frequency peaks align with harmonics of the blade passing frequency. Severe pressure perturbations occur at the focusing peak, particularly at blade tips and mid-span regions, where local positive pressure zones form on downstream surfaces. The turbine wake exhibits velocity distortion, vortex intensification, and a marked hysteresis effect in disturbances under focused waves. Although these waves enhance momentum exchange, they also accelerate vortex breakdown. These findings elucidate the transient loading mechanisms and wake dynamics of tidal current turbines under extreme waves, highlighting potential impacts on tidal energy generation.