A novel vortex-based velocity sampling method for the actuator-line modeling of floating offshore wind turbines in windmill state

The fluid-dynamic simulation of wind turbine aerodynamics is typically tackled by applying multi-fidelity computational tools. In this context, the so-called actuator line model combines a low-fidelity treatment of the rotor with a high-fidelity resolution of the wake. In this paper, a novel formulation of the actuator line model proposes a vortex-based method to sample the flow around the rotor to rigorously assign the forces imparted by the blades. This new technique is implemented into an in-house code developed within the OpenFOAM environment, and it is validated against wind-tunnel experiments on a laboratory-scale horizontal-axis wind turbine operated in fixed-bottom and floating conditions. The calculations are also compared against multi-fidelity simulations performed, on the same test case, in the frame of the OC6 Phase III project. The simulation results, obtained after a systematic analysis and selection of the model parameters, exhibit a remarkable agreement with the available experiments and place the present code in the proper ranking of fidelity levels, in-between momentum-balance methods and blade-resolved CFD models. Finally, the calculations for surge and pitch platform motions demonstrate the capability of the proposed technique to reliably predict the aerodynamics of turbine rotors in dynamic operation at affordable computational cost.