Proposal of actuator line-immersed boundary coupling model for tidal stream turbine modeling with hydrodynamics upon scouring morphology

Consideration of tidal stream turbine (TST) interactions with the surrounding environment and the resultant local scour is vital for safe operation and maintenance. A numerical model with coupling actuator line method (ALM) and immersed boundary method (IBM) is developed for simulating hydrodynamics synchronously with the local scour process around the TST. The ALM is applied to treat the rotating turbine rotor while the sediment dynamics is integrated into the IBM to simulate the scouring morphology. The simulating performance of the proposed ALM-IBM coupling model is validated and demonstrated by modeling the mono-pile supported horizontal-axis TST upon scouring seabed under steady currents. The impact of the horizontal-axis rotating turbine rotor on the scour around the supporting mono-pile under steady currents is then investigated. The results show that the rotating rotor can accelerate near-seabed flow resulting in the enhanced equilibrium scour scale around the mono-pile. The contribution of the mono-pile on the equilibrium maximum scour depth is stronger than that of the rotating rotor under the clear-water condition. The existence of the mono-pile can enhance the local mass and momentum exchanges between the wake- and surrounding-flow fields, leading to the asymmetrical scoured seabed morphology.