Numerical investigation of aerodynamic responses and wake characteristics of a floating offshore wind turbine under atmospheric boundary layer inflows

Abstract

The atmospheric boundary layer (ABL) inflow has significant effects on behaviors of floating offshore wind turbine (FOWT), especially for large-size wind turbine. In this study, numerical investigation of aerodynamics and wakes of a semi-submersible FOWT under ABL inflow is performed. The quasi-equilibrium ABL wind field is generated by large eddy simulations (LES) with sufficient simulation duration. The FOWT wakes are modeled by incorporating LES and actuator line model (ALM) in the computational fluid dynamics (CFD) framework, and the FOWT dynamic responses are simulated by FAST code. A two-way coupling procedure is employed, in which the wind velocity around wind turbine sampled in CFD framework and the wind turbine's body forces and positions solved by FAST code are delivered to each other. The simulation case of a bottom-fixed wind turbine is performed to provide some comparable data. It is revealed that the power variation of FOWT is dominated by atmospheric turbulence, more than platform motions. The slightly enhanced out-of-plane shear force and bending moment of FOWT are caused by platform motions. Owing to the entrance of ambient atmospheric flow into wind turbine wakes, significant deflection of wakes is visualized. In addition, the wake center of FOWT is far away from hub height level due to pitch motion of platform, which is a potential benefit factor for downstream wind turbines. The spatiotemporal characteristics of turbulence intensity in FOWT wakes are complex, and the discrepancies of wakes between floating and bottom-fixed scenarios are not significant.