Two phase fluid-actuator line-immersed boundary coupling for tidal stream turbine modeling with scouring morphology under wave-current loading

Consideration of tidal stream turbine (TST) interactions with marine environments and resultant morphological evolution is vital for power and safety maintenance. However, the TST induced morphological evolution with synchronous hydrodynamic characteristics under wave-current loading remains relatively unexplored. A new numerical framework is developed for simulating hydrodynamics around TST upon scouring morphology under wave-current loading. It integrates the two phase fluid model, actuator line method (ALM) for the turbine rotor, and immersed boundary method (IBM) for sediment dynamics and morphodynamics. Particularly, the integration yields the transient morphological evolution induced by the rotor motion. The framework was validated by simulating the wake-flow fields and scour development process around a horizontal-axis TST (HATST) under wave-currents, and the simulated results agreed well with experimental results. Subsequently, the numerical framework was employed to predict the scouring morphology with synchronous hydrodynamics around the HATST under the combined wave-current loading. The results indicate that the rotating turbine rotor intensifies the near-seabed flow around the turbine foundation under wave-currents. This intensified flow enhances the seabed shear stress, resulting in larger scour depth. Particularly, the wave motion enhances the instantaneous seabed shear stress and accelerates the scour development around turbine foundation. Both the turbine rotor and supporting foundation induce the sediment transport under wave-current loading, but the foundation's contribution to the scour depth is substantially larger. Overall, the proposed numerical framework provides a robust tool to analyze TST-induced sediment transport mechanisms under wave-currents.