Master thesis : CFD Modelling of Floating Offshore Wind Turbine Dynamics

Abstract

In the far-shore environment, Floating Offshore Wind Turbines(FOWT) are subjected to the critical loading of wind, current, and waves. Current methodologies for describing the dynamics of fixed-bottom offshore turbines may be insufficient for accurately describing the dynamics of floating systems due to the combination of harsh environmental loads and large rotor & platform motions. The full description of FOWT dynamics is usually divided into three main parts: wind turbine aerodynamics, supporting platform hydrodynamics, and mooring system dynamics. This makes FOWT’s design and analysis a technically difficult and computational problem. Due to the lack of computational power in the past, aerodynamic and hydrodynamic factors were frequently considered separately, potentially neglecting coupled effects. The present study focuses on aerodynamic performance of the NREL 5MW wind turbine using high-fidelity viscous-flow CFD code ReFRESCO with the following objectives: • Steady aerodynamic analysis of the turbine (blades only) with RANS turbulence models • Unsteady Aerodynamic analysis of the turbine using sliding grid methodology • Study of the flow around turbine in rotational motion This work also involved thorough verification and validation against obtained numerical results over a wide range of Tip speed ratios(TSRs). In addition, the current research work also involves advanced sensitivity studies for obtaining better results due to unsteady flow behaviour of the wind turbine. The sensitivity analysis are performed on domain studies, time-step studies, iterative convergence, Numerical uncertainty studies involving iterative error and discretization error, selection of turbulence model.